Slugging Percentage in Baseball: Formula and What's Good
Slugging percentage in baseball is total bases per at-bat. How MLB calculates SLG, what counts as a good figure, what it leaves out and who holds the records.
By CricketTaken EditorialPublished Baseball Stats & Positions25 min read
- Formula
- Total bases divided by at-bats
- Highest possible figure
- 4.000
- Highest career mark
- Josh Gibson, .718
- AL and NL single-season record
- Barry Bonds, .863 in 2001
Slugging percentage in baseball is total bases divided by at-bats. Under Rule 9.21(c) of Major League Baseball's Official Baseball Rules, a single is worth one base, a double two, a triple three and a home run four; add them up, divide by at-bats, and the result is the number of bases a hitter averages every time he is charged with an at-bat. In MLB a league-average hitter slugs about .400, a good one .450, and a middle-of-the-order bat .500 or more. Walks do not count toward it at all.
Two seasons show what it adds. Mark McGwire hit .187 in 2001, the last season of his career. Three years later Ichiro Suzuki hit .372 and set a record with 262 hits. By batting average the two seasons belong to different sports. By slugging percentage McGwire's was the better one: .492 against Ichiro's .455. McGwire had 56 hits all year, and 29 of them left the park.
What slugging percentage measures: total bases per at-bat
Batting average asks one question of each at-bat: hit or no hit. Slugging percentage asks how far the hit took the batter. It is the same division with a weighted numerator, a batting average in which a double is counted twice, a triple three times and a home run four.
That makes it a measure of power, though not only of home runs. A hitter who sprays doubles into the gaps and legs out the occasional triple can slug .480 with a dozen home runs. The statistic does not care how the bases were acquired. It cares that the batter was standing on second and not on first when the play ended.
Total bases, the figure on top of the fraction, is worth knowing as a counting stat in itself. It is what slugging percentage would be if it were not divided by anything: a running total of every base a hitter has reached on his own hits. A full-time player with 300 total bases has had a very good year. One with 400 has had a season people will remember; that mark has been reached only about thirty times in the long history of the American and National Leagues, and about a quarter of those came in the high-scoring seasons between 1997 and 2001.
On a stat sheet the abbreviation is SLG. Older encyclopedias print SA, for slugging average, which is the more accurate name and the one the statistic carried for decades. It is the third figure in the three-part line that broadcasters read out for a hitter, after batting average and on-base percentage.
A point about what it rewards. Because the denominator is at-bats, slugging percentage shares batting average's view of what a "chance" is. The trips to the plate that are not at-bats, the walk above all, are invisible to it. That is a real weakness, and a later section deals with it. For now it is enough to say that slugging answers a narrow question well: when this man is charged with an at-bat, how much damage does he do with it?
The slugging percentage formula, worked from a stat line
Stat lines list doubles, triples and home runs but almost never singles, so the first step is a subtraction.
SLG = (singles + 2 × doubles + 3 × triples + 4 × home runs) ÷ at-bats
Aaron Judge's 2022 season with the New York Yankees, the year he hit 62 home runs to set the American League record, shows each step.
- Find the singlesSubtract doubles, triples and home runs from hits. 177 minus 28, minus 0, minus 62 leaves 87 singles.
- Weight each hitSingles count once, doubles twice, triples three times and home runs four times. That gives 87, 56, 0 and 248.
- Add total bases87 plus 56 plus 0 plus 248 is 391 total bases.
- Divide by at-bats391 divided by 570 is 0.6860.
- RoundCarry the result to three decimal places. The season is recorded as .686.
The method in Rule 9.21(c) of the Official Baseball Rules, using Aaron Judge's 2022 season: 177 hits in 570 at-bats, with 28 doubles, no triples and 62 home runs.
There is a shortcut that skips the subtraction. Start with hits, then add one for every double, two for every triple and three for every home run, since each of those has already been counted once as a hit. For Judge that is 177 plus 28 plus 0 plus 186, which is the same 391.
Judge hit .311 that season. His slugging percentage was more than double his batting average, which few regulars manage in any year.
How many bases a hit is worth
The scorer credits the batter with the last base he reached safely on the hit itself. A runner thrown out trying to stretch a single into a double has hit a single. A ball that bounces over the outfield fence is two bases, however far the batter might have run; the placement of every runner on that play is covered in our guide to the ground rule double.
Game-ending hits have their own provision. When a batter drives in the winning run in the bottom of the last inning, Rule 9.06(f) credits him only with as many bases as the winning run needed to advance, even if the ball rolls to the wall. A home run hit out of the park is the exception, and counts in full, provided the batter completes the trip.
Robin Ventura did not complete it. In Game 5 of the 1999 National League Championship Series at Shea Stadium, with the bases loaded in the fifteenth inning, he hit a ball over the right-field fence. His New York Mets teammates mobbed him between first and second, he never reached the plate, and the official scorer recorded a single. It went into the books as one total base where there might have been four.
Why it is not really a percentage: a scale from .000 to 4.000
A percentage is a share of a whole and cannot exceed 100. Slugging percentage is an average, bases per at-bat, and its ceiling is four.
The name is a historical accident. Baseball had fallen into calling every three-decimal rate a "percentage," and when total bases per at-bat needed a title, it got the same suffix as fielding percentage and winning percentage, both of which really are proportions. Nobody has seen fit to correct it.
The practical consequence is that the figure cannot be read as a probability. A .500 slugger does not get a hit half the time. He averages half a base per at-bat, which he might do by hitting .300 with good power or .230 with enormous power.
Three reference points fix the scale.
A figure of .000 means no hits at all.
A figure of 1.000 means one total base for every at-bat. A hitter who goes 4-for-4 with four singles has slugged 1.000 for the night. So has one who goes 1-for-4 with a home run. The two box scores look nothing alike and the slugging percentage is identical, which says something about what the statistic can and cannot distinguish.
A figure of 4.000 means a home run every time. It can exist for a game, or for a player whose entire season is one swing.
Over a full season, nobody in the American or National League has reached even 1.000. The record is .863. Early in a season, or for a single game, the figure does climb above 1.000 on a scoreboard. Slugging is the only one of the three slash-line numbers that can.
It is spoken the way the other two are. A man at .550 is "slugging five-fifty," and gaps are measured in points. The distance between a .400 slugger and a .500 slugger, a hundred points, comes to 55 or 60 total bases over a season of regular work, roughly the difference between hitting 12 home runs and hitting 30, if the extra ones take the place of singles.
Multiplying back is the fastest sanity check on any line. Slugging percentage times at-bats gives total bases. A hitter listed at .500 with 600 at-bats should have 300 total bases, and if the page says otherwise, the page is wrong.
What a good slugging percentage is in MLB
The scale below is the informal one that the sport uses for an everyday player over a full season. Nothing in the rulebook defines it.
| Slugging percentage | How it is usually described | What it tends to mean |
|---|---|---|
| .600 and above | Historic | A season that leads the league most years and is remembered |
| .500 to .599 | Excellent | A middle-of-the-order bat; 30 or more home runs, or a great many doubles |
| .450 to .499 | Good | Clear above-average power |
| .390 to .449 | Around average | Where the league as a whole has sat in recent seasons |
| .350 to .389 | Below average | Little extra-base power; needs on-base skill or defense |
| Under .350 | Poor | A singles hitter without the average to make it work |
Across the majors the league slugging percentage has been close to .400 in the seasons since 2020, a little under in some and a little over in others. In a typical year somewhere between ten and twenty-five qualified hitters finish at .500 or better. A .600 season is a different order of thing. Most years produce two or three, and some produce none.
Position shifts the standard, as it does for every hitting statistic. A .430 figure from a shortstop or a catcher is an asset. The same number from a first baseman or a designated hitter, whose whole job is to hit, is a reason to look for someone else.
The league's slugging champion must qualify in the same way as its batting champion. Rule 9.22(a) requires 3.1 plate appearances for each game on the club's schedule, 502 in a normal season, for the batting, slugging and on-base titles alike. The history of that threshold, and the provision for hitters who fall just short, is told on our page about batting average.
One warning about the bottom of the table. A slugging percentage in the .330s was normal for a starting middle infielder in the 1970s and would be alarming now, because the whole league hits for more power than it did. A number that looks weak may simply be old.
What never enters it: walks, steals and bases taken on errors
Slugging percentage counts bases gained by the batter's hit, on the batter's hit. Every other way of advancing ninety feet is excluded.
| Event | Total bases credited | At-bat charged | Effect on slugging |
|---|---|---|---|
| Walk or intentional walk | 0 | No | Unchanged |
| Hit by a pitch | 0 | No | Unchanged |
| Stolen base | 0 | Not applicable | Unchanged |
| Reaching on an error | 0 | Yes | Goes down |
| Single, then to second on the throw home | 1 | Yes | Counted as a single |
| Single, then to third on an outfielder's error | 1 | Yes | Counted as a single |
| Sacrifice fly or sacrifice bunt | 0 | No | Unchanged |
The first three rows produce the oddity that puzzles newcomers most. A hitter who walks and then steals second is standing exactly where a double would have put him. For his team the two are nearly equivalent. His slugging percentage has recorded nothing, because neither the walk nor the steal is a hit.
This is by design and not an oversight. The statistic was built to describe hitting, the act of striking the ball, and the people who built it regarded the walk as a pitcher's mistake and the steal as a separate skill with its own column.
The fifth and sixth rows are the scorer's territory. When a batter singles and takes an extra base because the outfielder threw to another base or bobbled the ball, the scorer has to decide how much of the advance was the hit. The principle is that the batter gets the bases the hit itself would have earned against clean fielding. Anything beyond that is advancing "on the throw" or "on the error" and is worth nothing in the slugging column. Fast players pick up a great many bases this way that their slugging percentages never show.
The reverse also holds. A ball that an outfielder misjudges and lets fall is usually scored a double or a triple, not an error, since scorers seldom charge an error on a ball that was never touched. Those bases do count. So slugging percentage is slightly contaminated by fielding and by scoring judgment, in the same manner as batting average and to a somewhat larger degree, because each doubtful ruling can be worth two or three bases instead of one.
Reaching on an error is the harshest row. It is an at-bat with zero total bases, identical in the calculation to a strikeout.
Slugging against batting average, and isolated power
The two statistics have the same denominator and nested numerators, since every hit that counts in batting average counts at least once in slugging. A hitter's slugging percentage can therefore never be lower than his batting average. For a man who hits nothing but singles the two are equal.
Ichiro's 2004 is the purest high-average season of modern times. Of his 262 hits, 225 were singles. He had 24 doubles, 5 triples and 8 home runs, for 320 total bases in 704 at-bats. Subtract his batting average from his slugging percentage and 83 points remain.
McGwire's 2001 is the opposite. Fifty-six hits, of which 29 were home runs and 4 were doubles, for 147 total bases in 299 at-bats. Subtract the average from the slugging and about 300 points remain.
What isolated power strips away
That subtraction has a name. Isolated power, written ISO, is slugging percentage minus batting average, and it measures extra bases per at-bat with the singles removed. Algebraically it is doubles plus twice the triples plus three times the home runs, divided by at-bats.
The value of it is that slugging percentage on its own mixes two skills. Part of any slugging figure is just the hitter's batting average sitting inside it. A .330 hitter with ordinary power and a .250 hitter with great power can post the same .480, and ISO tells them apart at a glance: .150 for the first, .230 for the second.
As a rough guide, an isolated power of about .150 to .165 is league average in the modern game, .200 is strong, and .250 or more belongs to the handful of true power hitters. Under .100 is a slap hitter.
Neither number is better. Ichiro's .455 was built from contact and speed and McGwire's .492 from one swing in ten, and a team would have had good use for both. But they describe different players, and anyone reading a slugging percentage should look at the batting average beside it before deciding what kind of hitter produced it.
The weights are too generous: what a home run is really worth
One, two, three, four. The weights in slugging percentage were chosen because they are the number of bases, which is tidy and has nothing to do with how runs are scored.
A double is not worth twice as much as a single to an offense. A single with a runner on second usually scores him, the same as a double would. A single with a runner on first often sends him to third. Much of the work of a hit is done by reaching base at all and moving the runners already there, and that part is common to every kind of hit.
Analysts have measured this directly. The method, known as linear weights, goes through decades of play-by-play and asks how many runs a team scored, on average, from each situation before and after each kind of event. The difference is that event's run value. Pete Palmer published the best-known set in The Hidden Game of Baseball in 1984.
| Type of hit | Weight in slugging percentage | Palmer's run value | Run value measured in singles |
|---|---|---|---|
| Single | 1 | 0.46 runs | 1.0 |
| Double | 2 | 0.80 runs | 1.7 |
| Triple | 3 | 1.02 runs | 2.2 |
| Home run | 4 | 1.40 runs | 3.0 |
Read down the last column. In run-scoring terms a home run is worth about three singles, not four. A double is worth about 1.7 singles, not two. A triple, which slugging rates at half as much again as a double, is worth only about a quarter more, because the runners on base nearly always score on either.
The exact values drift from season to season with the level of offense, and later systems have refined them. The best known of those is weighted on-base average, set out in The Book in 2007, which reprices each event every year. The shape never changes: slugging percentage overpays for extra bases, and overpays most for the longest hits.
Palmer's table has one more line that matters here. A walk, which slugging percentage values at zero, is worth about a third of a run, or roughly 70 percent of a single.
None of this makes slugging percentage useless. Its weights are wrong in a consistent direction and by a modest amount, and for a quick comparison of two hitters' power it is rarely misleading. The error bites when the figure is added to something else as though the points were exact, which is the next subject.
Why slugging needs on-base percentage beside it
Andre Dawson won the National League's Most Valuable Player award in 1987. He hit 49 home runs for the Chicago Cubs and slugged .568, and those two figures carried the vote. His on-base percentage was .328, almost exactly league average, because he walked barely thirty times all season. He made more than 430 outs. The Cubs finished last.
That season is the standard exhibit for the slugger who never walks. Nothing in Dawson's slugging percentage is false. It simply describes what he did in the at-bats that ended with the ball in play or a strikeout and is silent about what all those plate appearances cost.
The two statistics cover each other's blind spots almost exactly.
- Slugging percentage knows how far each hit went and ignores walks.
- On-base percentage counts walks and treats a home run as no better than a single.
A hitter's full contribution needs both: how often he avoids an out, and how many bases he gains when he hits. The on-base half, which analysts have found to be the more valuable point for point, is explained in our guide to on-base percentage.
What happens when the two are added
The quick fix is to add them. On-base plus slugging, or OPS, takes the two figures from the slash line and sums them into a single number that tracks team run scoring far better than either part alone. Its formula, its scale and its flaws are covered on our page about OPS.
Two things are worth understanding about what slugging brings to that sum.
First, slugging is the larger number, so it dominates. League slugging has run roughly 80 to 95 points above league on-base percentage in recent seasons, and the spread between the best and worst sluggers is much wider than the spread between the best and worst at reaching base. A hitter can add 150 points of OPS through power far more easily than through patience. Since a point of on-base percentage is worth more than a point of slugging to begin with, OPS ends up tilted toward sluggers twice over.
Second, the two halves overlap. Every hit is counted in both, so batting average is in effect counted twice and walks only once.
The adjusted measures that came later, including the one in our explainer on OPS+, exist partly to correct that tilt and partly to account for where and when a hitter played.
Parks and eras: what moves slugging for a whole league
Babe Ruth slugged .847 in 1920, his first season with the Yankees. The American League as a whole slugged under .400 that year. Ruth hit 54 home runs, more than 14 of the other 15 major league teams hit as teams.
A figure like that cannot be understood without knowing what surrounded it, and slugging percentage is more sensitive to its surroundings than any other common hitting statistic. A cold, heavy ball takes away a few singles. It takes away a great many home runs.
American and National Leagues combined, shown in points, so 437 is a slugging percentage of .437. Selected seasons chosen to show the extremes, not a continuous series.
Show the numbers
| Item | League slugging |
|---|---|
| 1908 | 306 |
| 1930 | 434 |
| 1968 | 340 |
| 2000 | 437 |
| 2014 | 386 |
| 2019 | 435 |
The ball
In the first two decades of the twentieth century a single baseball might stay in play for most of a game, growing softer and darker by the inning, and pitchers were free to scuff it and wet it. League slugging percentages sat in the low .300s. From 1920 the spitball was outlawed for new pitchers, umpires began replacing dirty balls, and hitters led by Ruth started swinging from the heels. Within a decade the league was slugging .434. That transition is the subject of our guide to the dead-ball era.
The same thing has happened in miniature since. In 2019 major league hitters set a record with 6,776 home runs, and a committee of scientists commissioned by MLB concluded that the ball that year had been traveling through the air with less drag. The league slugged .435, close to the peak reached around 2000, and fell back when the ball changed again.
The park
Coors Field in Denver sits a mile above sea level. The thin air offers less resistance to a ball in flight, so fly balls carry farther, and it gives a breaking pitch less to bite on. The outfield was built unusually deep to compensate, which created acres of grass for doubles and triples to land on. Slugging percentages there were inflated enough that the Colorado Rockies have stored their baseballs in a humidity-controlled room since 2002.
Altitude is the extreme case, but every ballpark leans one way. The Baker Bowl in Philadelphia, home of the Phillies until 1938, had a right-field wall about 280 feet from the plate. Fenway Park's left-field wall turns routine fly balls into doubles and some line-drive home runs into long singles. How analysts measure and remove these effects is set out in our piece on park factors.
The era
The peak around 2000 had several causes that are hard to separate: new, smaller ballparks, expansion thinning the pitching, stronger hitters, and the use of performance-enhancing drugs before testing began. The trough in 1968 had causes too, a high mound and a tall strike zone among them, and the rules were changed that winter to end it.
The sensible habit is the same as for any rate statistic. Before judging a slugging percentage, find out what the league slugged that year and where the hitter played his home games.
Slugging turned around: slugging allowed and expected slugging
Pitchers have slugging percentages too, though the figure seldom appears on a broadcast.
Slugging allowed, or opponents' slugging, is the total bases a pitcher gives up divided by the at-bats against him. Opponents' batting average shows how often he is hit, and this shows how hard. Two pitchers can each hold hitters to a .240 average, one by giving up ground-ball singles and the other by giving up a steady diet of doubles and home runs, and their earned run averages will not be alike for long. A pitcher who keeps the ball on the ground tends to post a slugging percentage allowed well below what his opponents' average would predict, because a ground ball can be many things but is almost never a home run.
Teams use it most for matchups. A reliever's slugging allowed against left-handed and right-handed hitters, taken separately, is one of the plainer guides to when he should and should not be brought into a game.
Expected slugging
Since 2015 the tracking systems in every major league park have recorded the speed and the vertical angle of each batted ball. Expected slugging, written xSLG, takes those two readings and asks what balls struck that way have historically been worth in total bases. A drive hit 108 miles an hour at a 28-degree angle is a home run in nearly every park on nearly every day, so it is assigned close to four bases whether it clears the fence or dies in a center fielder's glove at the wall.
Three things are stripped out by doing it this way: the fielders, the weather and, to a large extent, the ballpark. A hitter at Coors Field and a hitter in a pitcher's park are graded on the same contact.
The usual use is to compare the two numbers. A hitter slugging .380 with an expected figure of .460 has been hitting the ball hard at people, and the results are likely to improve without him changing anything. One slugging .520 on an expected .430 has been getting more than his contact deserved. The measurements underneath, and the things they miss, are explained in our piece on exit velocity and launch angle.
Expected slugging has its own blind spot, which is direction. A fly ball pulled down the line needs far less distance than one hit to straightaway center, and hitters who consistently pull the ball in the air beat their expected figures year after year. That is a skill, not luck, and the model does not see it.
The record book: Gibson's .718, Ruth's .690 and Bonds's .863
For more than eighty years the career record was Ruth's .690, and nobody who followed him came within fifty points. He led the American League in slugging thirteen times. Since 2024, when MLB merged the statistics of the Negro Leagues of 1920 to 1948 into its official record, the top line has belonged to Josh Gibson, the Homestead Grays catcher, at .718. Gibson's figure rests on shorter league seasons and far fewer at-bats than Ruth's, and MLB applies a lower qualifying minimum to those seasons for that reason.
Single seasons
Gibson also holds the single-season mark, .974 in 1937, compiled across a Negro National League schedule of a few dozen recorded games. It is the closest anyone in the record book has come to a full base per at-bat.
In the American and National Leagues the list looks like this.
| Hitter | Season | Slugging percentage | Home runs |
|---|---|---|---|
| Barry Bonds, San Francisco | 2001 | .863 | 73 |
| Babe Ruth, New York (AL) | 1920 | .847 | 54 |
| Babe Ruth, New York (AL) | 1921 | .846 | 59 |
| Barry Bonds, San Francisco | 2004 | .812 | 45 |
| Barry Bonds, San Francisco | 2002 | .799 | 46 |
Ruth's .847 stood for 81 years. Bonds passed it in the season he hit 73 home runs, finishing with 411 total bases in 476 at-bats. The composition of that line is as strange as the total. He had 156 hits, and 73 of them were home runs against 49 singles. He also walked 177 times, which is why the at-bat total is so low; a hitter who is pitched around that often gets fewer chances to add total bases, and the ones he does get tend to come on pitches thrown by mistake.
Ruth's 1921 deserves a note of its own. His slugging percentage was a single point below the previous year's, but he piled up 457 total bases, which remains the record for a season. The career record for total bases is Hank Aaron's 6,856. The home run marks that underlie most of these figures are listed in our guide to the MLB home run record.
Other Negro Leagues seasons besides Gibson's 1937 also sit near the top of the combined single-season list. They were set in schedules much shorter than 154 or 162 games, where a hot stretch makes up a larger share of the season. Career figures for active players are still moving and are not given here.
Where it came from: Chadwick's total bases and the long wait
The idea is nearly as old as the box score. Henry Chadwick, the Brooklyn sportswriter who designed most of baseball's early record-keeping, was tabulating total bases in the 1860s and publishing a "total bases average" for the leading clubs. He understood from the start that a man who hit the ball over the outfielders' heads had done more than a man who dropped it in front of them.
Then he changed his mind. Chadwick came to distrust the long hit as a measure of skill. Extra bases in the 1860s and 1870s often owed as much to bare-handed fielders and rough outfields as to the batter, and he disliked the free-swinging style that chased them. He threw his influence behind the plain count of hits per at-bat, and when the National League was founded in 1876 it was batting average, not total bases, that became the official measure of a hitter.
Total bases per at-bat lingered in guides and newspapers for the next half-century without official standing. For most of that time it did not matter much. In a game where the league leader might hit ten home runs, hitters differed from one another mainly in how often they got a hit, and batting average captured most of the difference.
Ruth ended that. Once a single player could hit 54 home runs and another regular in the same league two, a statistic that scored those hits identically was plainly missing something. The National League adopted slugging percentage as an official statistic in 1923. The American League, Ruth's own, did not follow until 1946, more than a decade after he had retired. League offices were not quick with these things.
The measure has been refined around rather than replaced. Branch Rickey's 1954 argument for judging hitters by on-base average and extra-base power separated the two skills that slugging blends. Linear weights repriced the hits. Tracking cameras now estimate what a swing deserved. Through all of it the original sum has stayed on the stat sheet, in the third slot of the slash line, for the simple reason that anyone can work it out from a box score with a pencil.
It appears in that position for every hitter on the batting pages of our baseball coverage, a hundred and sixty years after Chadwick first added up the bases.