What Is Slugging Percentage? SLG and OPS Explained

Quick answer: Slugging percentage (SLG) is total bases divided by at-bats, where a single counts as one base, a double two, a triple three and a home run four. OPS adds on-base percentage to slugging. Jose Canseco's 1988 season, 347 total bases in 610 at-bats, produced a .569 SLG and a .959 OPS.

What Is Slugging Percentage?

Slugging percentage measures how many bases a hitter gains per at-bat. MLB's official glossary defines it as the total number of bases a player records per at-bat, and gives the formula as:

SLG = (1B + 2B x 2 + 3B x 3 + HR x 4) / AB

The top of that fraction is total bases (TB). MLB's total bases entry spells it out: one base for a single, two for a double, three for a triple and four for a home run. Advancing on the bases, even by stealing, does not add total bases. Only hits count.

Two details trip people up. First, despite the name, slugging is not really a percentage. It is an average number of bases per at-bat, so it can run from .000 to a theoretical 4.000 for a hitter who homered in every at-bat. Second, slugging percentage ignores walks and hit-by-pitches entirely, because those do not count as at-bats. That is a big part of why it pairs so well with on-base percentage.

How Do You Calculate Slugging Percentage?

The easiest way to learn the formula is to run a real season through it. Here is Jose Canseco's 1988 season with the Oakland A's, the year he won the AL MVP, using his line from Baseball-Reference: 610 at-bats, 187 hits, 34 doubles, 0 triples and 42 home runs.

1. Find the singles. Subtract the extra-base hits from total hits: 187 - 34 - 0 - 42 = 111 singles.
2. Weight each hit type. Singles: 111 x 1 = 111. Doubles: 34 x 2 = 68. Triples: 0 x 3 = 0. Home runs: 42 x 4 = 168.
3. Add them up for total bases. 111 + 68 + 0 + 168 = 347 total bases.
4. Divide by at-bats. 347 / 610 = .569.

That matches the .569 slugging percentage Baseball-Reference lists for Canseco in 1988, along with his 347 total bases.

A Second Worked Example: Rickey Henderson in 1990

Rickey Henderson is remembered for speed, but his 1990 MVP season was also a power season. Per Baseball-Reference's 1990 A's page, he had 489 at-bats, 159 hits, 33 doubles, 3 triples and 28 home runs.

• Singles: 159 - 33 - 3 - 28 = 95
• Total bases: 95 + (33 x 2) + (3 x 3) + (28 x 4) = 95 + 66 + 9 + 112 = 282
• SLG: 282 / 489 = .577

Henderson's 65 stolen bases that year added nothing to that number, which is a good reminder that slugging measures what a hitter does with the bat, not on the bases.

Why Isn't Slugging the Same as Batting Average?

Batting average treats every hit the same: a bloop single and a home run both count as one hit. Slugging gives the home run four times the weight. The 1989 A's offer a perfect comparison, using Baseball-Reference's 1989 numbers:

• Carney Lansford: .336 batting average, .405 slugging. Of his 185 hits, 153 were singles and only 2 were home runs, for 223 total bases in 551 at-bats.
• Mark McGwire: .231 batting average, .467 slugging. Of his 113 hits, 33 were home runs, for 229 total bases in 490 at-bats.

Lansford got a hit far more often. McGwire did more damage when he connected. A related stat, isolated power (ISO), strips out singles to isolate that difference. MLB's ISO definition gives the shortcut formula as slugging percentage minus batting average. McGwire's 1989 ISO was .467 - .231 = .236. Lansford's was .405 - .336 = .069.

What Is On-Base Percentage?

ging percentage (SLG) is total bases divided by at-bats, where a single counts as one base, a double two, a triple three and a home run four.

To understand OPS you need the other half: on-base percentage (OBP). MLB defines OBP as how frequently a batter reaches base per plate appearance, counting hits, walks and hit-by-pitches but not errors or fielder's choices. Sacrifice bunts are left out of the calculation, while sacrifice flies count against a player's on-base percentage. Put together, the formula is:

OBP = (H + BB + HBP) / (AB + BB + HBP + SF)

For Canseco in 1988, with 187 hits, 78 walks, 10 hit-by-pitches, 610 at-bats and 6 sacrifice flies:

• Times on base: 187 + 78 + 10 = 275
• Denominator: 610 + 78 + 10 + 6 = 704
• OBP: 275 / 704 = .391

Again, that matches his Baseball-Reference line exactly.

What Is OPS and How Is It Calculated?

OPS stands for on-base plus slugging. MLB describes it as a stat that adds on-base percentage and slugging percentage to get one number, combining a hitter's ability to reach base with his ability to hit for power. The formula is as simple as it sounds:

OPS = OBP + SLG

Canseco's 1988 OPS was .391 + .569, which Baseball-Reference lists as .959. If you add the rounded numbers you get .960. The one-point gap comes from rounding: the unrounded values are about .3906 and .5689, which sum to .9595, and stat sites round the total from the unrounded figures. You will run into this small mismatch often when checking OPS by hand.

Henderson's 1990 season shows the formula at its best. His on-base percentage works out to 260 times on base (159 hits, 97 walks, 4 hit-by-pitches) divided by 592 (489 at-bats, 97 walks, 4 hit-by-pitches, 2 sacrifice flies), or .439. Add his .577 slugging and you get a 1.016 OPS, the figure Baseball-Reference shows for his MVP year.

Two Routes to the Same OPS

Go back to the 1989 comparison. Lansford posted a .398 OBP and a .405 SLG for an .803 OPS. McGwire posted a .339 OBP and a .467 SLG for an .806 OPS. Two very different hitters, one built on contact and getting on base, one built on power, landed within three points of each other. That is OPS doing its job: it gives a quick read on total offensive output regardless of how a hitter gets there.

How Do Team Slugging Numbers Compare Across Eras?

Slugging works for teams as well as players. Baseball-Reference lists the team slugging percentage of each of the three Bash Brothers pennant winners at .399 in 1988, .381 in 1989 and .391 in 1990. The 2002 Moneyball A's slugged .432 as a team, with 205 home runs.

That does not mean the 2002 lineup was dramatically more powerful relative to its league. According to Baseball-Reference's American League batting averages, the AL as a whole slugged .391 in 1988 and scored 4.36 runs per game, while in 2002 the league slugged .424 and scored 4.81 runs per game. Measured against their own leagues, the 1988 A's (.399) and the 2002 A's (.432) were each eight points above the AL average. Raw team slugging from different eras is not directly comparable, which is the same problem OPS+ solves for individual hitters, covered below.

For one more individual example from that 2002 team, take MVP shortstop Miguel Tejada: 204 hits, 30 doubles, no triples and 34 home runs in 662 at-bats. That is 140 singles, so his total bases were 140 + 60 + 0 + 136 = 336, and 336 / 662 = .508, matching his listed slugging percentage on Baseball-Reference.

What Are the Limits of SLG and OPS?

Both stats are useful shortcuts, and both have known weaknesses.

• Slugging overweights some hits. MLB's own glossary notes that a double is not worth exactly twice as much as a single in terms of scoring runs. The 1-2-3-4 weights are a convenient approximation.
• OPS treats OBP and SLG as equals. Simply adding them gives each the same weight, even though they are measured on different scales.
• Neither adjusts for context. A .800 OPS means something different in a high-scoring era or a hitter-friendly park than in a pitcher's era or a big park.

That last problem is what OPS+ solves. MLB's OPS+ entry explains that it normalizes OPS across the league, accounts for ballparks, and scales the result so 100 is league average. The formula is 100 x (OBP/lgOBP + SLG/lgSLG - 1). On that scale, Canseco's 1988 OPS+ was 170 and Henderson's 1990 OPS+ was 189, per Baseball-Reference. McGwire and Lansford, nearly tied in raw OPS in 1989, came in at 129 and 131.

Quick Reference: The Formulas in One Place

• Total bases (TB): 1B + (2B x 2) + (3B x 3) + (HR x 4)
• Slugging percentage (SLG): TB / AB
• Batting average (AVG): H / AB
• Isolated power (ISO): SLG - AVG
• On-base percentage (OBP): (H + BB + HBP) / (AB + BB + HBP + SF)
• On-base plus slugging (OPS): OBP + SLG
• OPS+: 100 x (OBP/lgOBP + SLG/lgSLG - 1), with park adjustments applied by the stat provider

If you only remember one thing, remember the denominators. Batting average and slugging divide by at-bats, so walks never help or hurt them. On-base percentage divides by a broader set of plate appearances, so walks raise it and sacrifice flies lower it. OPS simply stacks the two, which is why a patient hitter and a pure power hitter can end up with nearly the same number.

Where Can You Find A's Slugging Leaders?

For quick definitions of OBP, SLG, OPS, OPS+ and dozens of other stats, keep our baseball stats glossary handy. To see which Athletics hitters top the franchise lists for home runs, hits and RBI, the raw ingredients behind slugging, check our A's all-time leaders and records.

Sources

• MLB.com glossary: Slugging Percentage (SLG), Total Bases (TB), On-base Percentage (OBP), Sacrifice Fly (SF), On-base Plus Slugging (OPS), Isolated Power (ISO), OPS+
• Baseball-Reference, Oakland Athletics season pages for 1988, 1989, 1990 and 2002 (all player and team stat lines used in the worked examples)
• Baseball-Reference, American League batting averages by season (league slugging and runs per game)

LV Athletics is an independent fan site and is not affiliated with the Athletics or Major League Baseball.