What Is Slugging Percentage? SLG Formula, Examples and ISO

Slugging percentage (SLG) measures how many bases a hitter gets per at-bat: you add up his total bases, counting a single as 1, a double as 2, a triple as 3 and a home run as 4, then divide by at-bats. A hitter with 248 total bases in 550 at-bats slugs .451, which was about 50 points above the major league average in 2026.

Where batting average only asks whether a hitter got a hit, slugging asks how much the hit was worth. That makes it the standard quick measure of power. This guide walks through the formula with real arithmetic, explains why the name is misleading, shows how SLG sits next to batting average and on-base percentage in a slash line, and uses MLB's own numbers to show what a good slugging percentage looks like today.

The slugging percentage formula

The Official Baseball Rules define it in one line. Rule 9.21(c) says to compute slugging percentage by dividing the total bases of all safe hits by the total times at bat. Written out:

SLG = total bases / at-bats

Total bases (TB) is the sum of the bases on every hit:

• Single: 1 base
• Double: 2 bases
• Triple: 3 bases
• Home run: 4 bases

So the long form is SLG = (1B + 2 x 2B + 3 x 3B + 4 x HR) / AB. Box scores and stat pages usually list hits, doubles, triples and home runs rather than singles, so you often have to work singles out first: singles = hits minus doubles minus triples minus home runs.

What counts as an at-bat

The denominator is at-bats, not plate appearances, and that detail matters. Under Rule 9.02(a)(1), a batter is not charged with an at-bat when he:

• draws a walk
• is hit by a pitch
• lays down a sacrifice bunt or hits a sacrifice fly
• is awarded first base because of interference, obstruction or a shift violation

Everything else that ends a plate appearance is an at-bat, including strikeouts, ordinary outs, fielder's choices and reaching base on an error. That means a walk has no effect on slugging at all, while reaching on an error lowers it, because the official scorer records an at-bat with no hit and no bases.

Worked examples, step by step

All the players below are hypothetical. The numbers are chosen to make the arithmetic easy to follow, not to describe anyone real.

One game

A hitter comes to the plate five times. He singles, homers, walks, strikes out and grounds out.

The walk is not an at-bat, so he has 4 at-bats. His hits are a single (1 base) and a home run (4 bases), for 5 total bases.

SLG for the game = 5 / 4 = 1.250.

His batting average for the day is 2 / 4 = .500. One game is far too small a sample to mean anything, but it shows how quickly a home run lifts slugging above 1.000.

A full season

Now a season line for a solid everyday hitter:

• At-bats: 550
• Hits: 150, made up of 95 singles, 32 doubles, 3 triples and 20 home runs

Check the hits first: 95 + 32 + 3 + 20 = 150.

Then total bases, one hit type at a time. Singles: 95 x 1 = 95. Doubles: 32 x 2 = 64. Triples: 3 x 3 = 9. Home runs: 20 x 4 = 80. Total: 95 + 64 + 9 + 80 = 248.

SLG = 248 / 550 = 0.45091, which rounds to .451.

Stat sites show slugging to three decimal places and drop the leading zero, so you will see .451, spoken as "four fifty-one." A slugging percentage of 1.000 or more keeps its leading digit.

Enter a stat line below to get total bases and slugging percentage. Use total hits, including extra-base hits; the calculator works out the singles.

Why slugging percentage is not really a percentage

A true percentage tops out at 100 percent. Slugging does not. It is an average number of bases per at-bat, so the theoretical range runs from .000 (no hits at all) to 4.000 (a home run in every at-bat). Batting average and on-base percentage are at least proportions of something, even if baseball writes them as decimals. Slugging is a rate.

Think of the name as a label, not a description. It is written the same way as batting average, as a three-digit decimal, and that is about all the two share in format. The practical effect is that you should never read .451 as "45 percent of something." Read it as 0.451 bases per at-bat, or roughly 45 bases for every 100 at-bats.

This is also why a great season can push on-base plus slugging past 1.000. Slugging alone can exceed 1.000 over a game or a week, and the very best full seasons in history have come closer to .900 than to .500.

SLG vs batting average vs OBP

Broadcasts and stat pages often show a hitter's slash line, three numbers in a row such as .273/.340/.451. In order, they are batting average (AVG), on-base percentage (OBP) and slugging percentage (SLG). Each answers a different question:

• AVG = hits / at-bats. Measures how often he gets a hit.
• OBP = (hits + walks + hit by pitch) / (at-bats + walks + hit by pitch + sacrifice flies). Measures how often he avoids making an out.
• SLG = total bases / at-bats. Measures how many bases each at-bat is worth.

AVG and SLG share a denominator, which makes them easy to compare. Slugging can never be lower than batting average, because every hit is worth at least one base. If a hitter's SLG equals his AVG exactly, every one of his hits was a single.

The gap shows up clearly when two hitters have the same average. Picture two hypothetical players, each with 162 hits in 600 at-bats, so both bat .270:

• Hitter A: 140 singles, 18 doubles, 2 triples, 2 home runs. Total bases: 140 + 36 + 6 + 8 = 190. SLG = 190 / 600 = .317.
• Hitter B: 92 singles, 35 doubles, 1 triple, 34 home runs. Total bases: 92 + 70 + 3 + 136 = 301. SLG = 301 / 600 = .502.

Same batting average, and nearly 60 percent more total bases for Hitter B. That difference is exactly what slugging percentage was built to show.

Adding OBP and SLG together gives on-base plus slugging, the shortcut stat most fans use to rank hitters. Our guide to OPS in baseball walks through that calculation in full, along with the park-adjusted OPS+.

For comparison, batting average needs only hits and at-bats. Put the same line into the calculator below and set it next to the slugging figure above.

Isolated power: slugging minus batting average

Slugging still gives credit for singles, so a high-average hitter with little power can post a respectable SLG. Isolated power (ISO) strips the singles out. MLB's glossary and the FanGraphs library both define it two ways that give the same answer:

• ISO = SLG - AVG
• ISO = (2B + 2 x 3B + 3 x HR) / AB, the extra bases beyond first per at-bat

For the season hitter above: 32 + (2 x 3) + (3 x 20) = 98 extra bases, and 98 / 550 = .178. Using the other route, .451 - .273 = .178. Both match.

For Hitters A and B from the last section, ISO is 28 / 600 = .047 and 139 / 600 = .232. Same average, completely different power profiles.

FanGraphs publishes a rule-of-thumb scale for ISO and stresses that league average moves from year to year:

• .250: excellent
• .200: great
• .170: above average
• .140: average
• .120: below average
• .100: poor
• .080: awful

For context, the league-wide ISO across MLB in 2026 was .156, worked out from MLB's official season totals: (65,409 total bases - 39,849 hits) / 163,329 at-bats.

What is a good slugging percentage

There is no official scale, and the league-wide number shifts as offense rises and falls. The most honest benchmark is the league itself. Using MLB's official regular-season totals for all 30 teams:

• 2026: 65,409 total bases in 163,329 at-bats, a league SLG of .400
• 2025: 66,089 total bases in 163,664 at-bats, a league SLG of .404

The hitters who play every day do better than that overall figure, which includes bench players and part-timers. In 2026, 135 hitters reached the 502 plate appearances needed to qualify for rate-stat titles. Their median slugging percentage was .427. Only 14 of them slugged .500 or better, and just two topped .550. In 2025, 18 of 145 qualified hitters reached .500.

From those numbers, a rough reading guide for the current era:

• Around .400: league average for all hitters
• About .425 to .450: a typical regular
• .500 or higher: roughly the top 10 percent of qualified hitters
• .550 or higher: a handful of players in a given season

Position changes the picture. Teams expect power from first basemen and designated hitters, so a .450 SLG is ordinary there and very good from a catcher or shortstop.

Qualifying and the record book

Rule 9.22(a) sets the bar for a slugging title: 3.1 plate appearances for every game on the schedule. In a 162-game season that is 162 x 3.1 = 502.2, rounded to 502. The rule also lets a hitter who falls short still win if adding hitless at-bats to reach 502 would leave him on top. If you want to know where 162 comes from, see how many games are in an MLB season.

At the very top, MLB's records list Barry Bonds at .863 in 2001, the highest single-season mark in American League or National League history, and Babe Ruth at .690 for his career. Since May 2024, MLB's official record book has also included Negro Leagues statistics from 1920 to 1948, and Josh Gibson now leads both the career and single-season slugging lists. Research into those seasons is ongoing, so Gibson's exact figures have been revised since the records were merged. In 2025, Aaron Judge led all qualified hitters at .688.

What slugging percentage misses

The walk problem is the big one. A patient hitter who draws 100 walks gets no slugging credit for any of them, which is why SLG is best read next to OBP rather than alone. The weighting is the second issue. Slugging says a home run is worth four singles, but in terms of runs actually produced the gap is smaller than that. Modern stats such as weighted on-base average (wOBA) give each event its own value for this reason.

Sample size matters as much here as anywhere. One big week can push a part-timer's SLG past .700. Wait for a few hundred at-bats before reading much into it.

Pitchers face the same math in reverse. Slugging allowed is the total bases opponents collected divided by their at-bats, and lower is better. It pairs well with ERA because it shows whether a pitcher is giving up loud contact or just a lot of singles.

Slugging percentage quick reference

Keep this list handy the next time a slash line pops up on a broadcast:

• SLG = total bases / at-bats (Official Baseball Rules 9.21(c))
• Total bases = 1B + 2 x 2B + 3 x 3B + 4 x HR, or hits + 2B + 2 x 3B + 3 x HR
• Walks, hit-by-pitches and sacrifices are not at-bats and do not count
• Range: .000 to 4.000, written to three decimals without the leading zero
• ISO = SLG - AVG, the extra bases per at-bat
• League SLG: .400 in 2026, .404 in 2025
• .500 or better put a hitter in roughly the top 10 percent of qualified hitters in 2026
• Slash line order: AVG / OBP / SLG