Batting Average, On-Base Percentage and Slugging Explained

By 4Baseball Staff · November 5, 2026 · 10 min read

How batting average, on-base percentage and slugging percentage are calculated, what each one captures and misses, and how league averages have moved from 1900 to the 2020s, with worked examples.

Three numbers separated by slashes, such as .300/.380/.480, tell a baseball fan most of what a hitter's season looked like. They are batting average, on-base percentage and slugging percentage, usually called the triple slash line, and each answers a different question. Batting average asks how often the hitter gets a hit. On-base percentage asks how often he avoids making an out. Slugging percentage asks how many bases he gets when he does hit.

Each statistic is simple to calculate and easy to misread. A .300 hitter can be worth less than a .260 hitter who walks a hundred times a year. A slugging percentage of .500 is not a percentage in the usual sense and can exceed 1.000. And a .270 average, which would have been ordinary in the 1990s, looks quite good in the 2020s. The right way to use these numbers is to know the formulas, know what each ignores and compare a hitter to the league of the same year.

This article gives the formulas with worked examples, lists the strengths and the blind spots of each statistic, and uses the historical record to show how league averages have changed over more than a century. It ends with how the three numbers lead to newer measures such as OPS+, wOBA and wRC+.

Batting average: hits divided by at-bats

Batting average is hits (H) divided by at-bats (AB). A hitter with 150 hits in 500 at-bats has a .300 average, written without the leading zero. The statistic dates back to the nineteenth century and remains the number printed first on most scoreboards and trading cards.

The definition of an at-bat is where the details live. A plate appearance counts as an at-bat unless it ends in a walk, a hit by pitch, a sacrifice bunt, a sacrifice fly or catcher's interference. Those plate appearances do not hurt a batting average, and they do not help it either. A hitter who walks does not get credit for reaching base in this statistic, which is the first of its limitations.

To qualify for the batting title, a hitter needs 3.1 plate appearances for each game his team plays, which is 502 in a 162-game season. If he falls short, the rule adds hitless at-bats to his total until he reaches the minimum, and he wins only if his average still leads the league. This rule protects the title from a part-time hitter who went 3 for 7.

The benchmarks most fans carry in their heads are .300 for a very good hitter and .400 for a legend. The last player to hit .400 for a full season was Ted Williams, who batted .406 for the Boston Red Sox in 1941: 185 hits in 456 at-bats. Before him, Rogers Hornsby hit .424 in 1924, the highest single-season average in the historical record among National and American League hitters with 400 at-bats since 1920.

What batting average does well, and where it falls short

Batting average rewards contact, and it is a clean, widely understood number. It has a long history, which means every great hitter can be compared on it. Among players with at least 4,000 at-bats, the career leaders in the historical record are Ty Cobb at .366, Rogers Hornsby at .358, Shoeless Joe Jackson at .356, Oscar Charleston at .350 and Ed Delahanty at .346. Charleston's total includes Negro Leagues games recorded in the database, and its coverage is partial, so it should be read with that in mind. Tony Gwynn, one of the great contact hitters of the modern era, finished at .338 on 3,141 hits.

But batting average ignores two things. It ignores walks, because a walk is not an at-bat. It also treats every hit the same, a bunt single the same as a home run. Two hitters can have a .300 average and very different value. One gets 100 singles and 50 doubles, triples and home runs, while the other gets 140 singles and 10 extra-base hits.

There is also the question of luck. A batting average depends in part on how many balls in play fall for hits, which varies from year to year for reasons outside a hitter's control. The statistic that isolates that part is batting average on balls in play (BABIP). A BABIP far above a hitter's career norm is usually partly luck, and it tends to come back down the next year.

On-base percentage: the cleaner measure of avoiding outs

On-base percentage (OBP) is hits plus walks plus hit-by-pitches, divided by at-bats plus walks plus hit-by-pitches plus sacrifice flies. Written as a formula, OBP = (H + BB + HBP) / (AB + BB + HBP + SF). It answers the most basic question a hitter faces, which is whether he reaches base, and it counts a walk exactly as a single.

By the official convention, sacrifice flies stay in the denominator and sacrifice bunts are left out. The underlying idea is that outs are the scarce resource in baseball, since a team gets 27 of them per game, and OBP measures how often a hitter does not spend one.

Here is a worked example with two hitters, each with about 500 at-bats.

Hitter A has the better batting average by 40 points, and Hitter B is the better at reaching base, with a .383 OBP against .377. The walk total is the difference. That is why, in the decades since, many front offices have prized hitters with high walk rates that batting average hides. The idea is older than the data: Ted Williams, who walked 2,021 times in his career, finished with a .482 on-base percentage, the best in the historical record among players with 4,000 at-bats. Babe Ruth is second at .474, followed by Billy Hamilton at .455, Lou Gehrig at .447 and Barry Bonds at .444.

The extreme case: Barry Bonds in 2004

The most extreme OBP season in the database is Barry Bonds in 2004. He had 373 at-bats, 135 hits, 232 walks, 9 hit-by-pitches and 3 sacrifice flies, which computes to a .609 on-base percentage. His batting average was .362 and his slugging was .812. He was walked intentionally many times that year, which is why the at-bat total is so low, and the line shows what happens when pitchers decline to throw hittable pitches. He still reached base in more than three of every five plate appearances.

OBP has weaknesses too. It treats a walk and a home run as the same event, which they are not. It also tells you nothing about speed, power or context. A leadoff hitter with a .380 OBP and a cleanup hitter with a .380 OBP are not equally valuable if one drives in runs and the other cannot. The statistic is best seen as one third of a set.

Slugging percentage: total bases per at-bat

Slugging percentage (SLG) is total bases divided by at-bats. Total bases are singles plus twice the doubles plus three times the triples plus four times the home runs, or TB = 1B + 2(2B) + 3(3B) + 4(HR). It is not a percentage of anything in the strict sense. A hitter who hit only home runs and never made an out would slug 4.000, which is why it can exceed 1.000 over a short period. Over a season, a slugging percentage of .600 is superb, and .500 is a good mark.

Using the same Hitter A, with 150 hits made up of 100 singles, 30 doubles, 2 triples and 18 home runs: total bases are 100 + 60 + 6 + 72 = 238, and slugging is 238 divided by 500, or .476. The simple difference between slugging and batting average is isolated power (ISO), a quick measure of extra-base hit production. For Hitter A it is .476 minus .300, or .176.

Hitter B, with 130 hits made up of 90 singles, 25 doubles and 15 home runs, has total bases of 90 + 50 + 60 = 200 and a slugging percentage of .400. B has the better OBP and A has the better slugging, which is what makes the pair a fair comparison.

Career slugging leaders reflect a mix of eras. Babe Ruth leads the historical record among players with 4,000 at-bats at .690. Ted Williams is next at .634, then Lou Gehrig at .632, Aaron Judge at .615 through the 2025 season and Jimmie Foxx at .609. Barry Bonds finished his career at .607.

The weakness of slugging is that it counts bases, not runs. Valuing a double at exactly twice a single and a home run at exactly four times a single is a convention, not a measurement of how many runs each event produces. A walk is worth nothing in slugging at all. It is a better power measure than batting average but a worse measure of overall production than OBP.

Putting them together: OPS and the triple slash

Adding OBP and SLG gives on-base plus slugging (OPS). It is a convenient single number, and it correlates well with run scoring. Hitter A's OPS is .377 plus .476, or .853, and Hitter B's is .383 plus .400, or .783. The weakness is that OPS adds two numbers with different denominators and weights them equally, even though a point of OBP is worth more than a point of slugging in producing runs. The newer statistic OPS+ explained adjusts for the league and park to put hitters from different years on one scale.

Babe Ruth's career line in the historical record is .342/.474/.690, an OPS of 1.164, the highest of any player with 4,000 at-bats. Ted Williams' is .344/.482/.634. Tony Gwynn's is .338/.388/.459, and Juan Soto's through the 2025 season is .282/.417/.531.

For a deeper treatment, the wOBA explainer shows how to weight each way of reaching base by its run value, and the wRC+ article shows how to adjust that for park and league. These measures were built to fix the limits of the three numbers in this article, and it helps to understand the three first.

League averages by decade

A batting average of .270 means little without knowing the league. This table, computed from the historical Batting table for the American and National Leagues only, shows the combined averages by decade. Negro Leagues rows are excluded.

The on-base figures for the earliest decades are slightly high because the database lacks sacrifice flies for many older seasons, so they are missing from the denominator. The pattern is clear anyway. The 1920s and 1930s were a hitters' era, with a league batting average of .285 in the 1920s. The 1960s were the low point for offense, and the single season of 1968 is the extreme: .237/.299/.340 for the two leagues combined. In 1969 the mound was lowered and the strike zone reduced, and the league line jumped to .248/.320/.369.

The most striking recent change is not in batting average but in how it is made up. The league slugging percentage in the 2010s, .408, was higher than in the 1980s, even though the league average was lower. The 2019 season, which the historical record shows as a year with 4.83 runs per team game, 1.39 home runs per team game and 8.81 strikeouts per team game, came out at .252/.323/.435 for the two leagues. By 2025 it was .245/.315/.404.

A season in context: 2019

The batting titles in 2019 show how far the best batting averages have fallen from the 1920s. Tim Anderson of the White Sox won the American League title at .335, with DJ LeMahieu at .327 and Yoan Moncada at .315. In the National League, Christian Yelich led at .329, with Ketel Marte also at .329 to three decimals and Anthony Rendon third at .319. Whit Merrifield led the majors with 206 hits.

But the power leaders show where the game was. Pete Alonso hit 53 home runs, Eugenio Suarez 49 and Jorge Soler 48. The league's slugging percentage of .435 in 2019 was higher than the average of any decade in the table above. In that environment a .300 hitter was valuable, but so was a hitter with 40 home runs and 90 walks, who might have a lower average and still help a club more. You can test your own examples with the site's stat calculator.

Common mistakes

The first mistake is treating batting average as a percentage of plate appearances. It is hits per at-bat, and walks are removed. The second is comparing across eras without a baseline: a .280 average was merely average in the 1930s, when the league hit .280, and far above average in 1968. The third is ignoring playing time, since a .320 average over 100 at-bats is not a batting title and not strong evidence.

The fourth is forgetting that slugging ignores walks entirely, so a patient hitter's value is understated. The fifth is treating OPS as the final answer. It is a convenient shortcut, and the context-adjusted versions are better. The sixth is forgetting that a rate statistic hides the volume: a .400 OBP over 200 plate appearances is not the same as over 700.

The sample size problem is the one that traps beginners most. Over a short stretch of games, a batting average can swing by 100 points. A full season of about 500 at-bats has a standard deviation in batting average of roughly 20 points from luck alone, so a hitter who improves by 20 points is not necessarily better.

Common questions

What is a good batting average? In most seasons, anything above .300 is excellent and the league average sits near .250 to .265. The decade table above shows how much the baseline moves.

Is on-base percentage better than batting average? For judging how often a hitter avoids making an out, yes, because it counts walks and hit-by-pitches. Batting average still has uses, such as showing how often a hitter puts the ball in play for a hit.

Why is slugging percentage not capped at 1.000? Because it measures total bases per at-bat. A home run is worth four bases, so a hitter with enough extra-base hits can exceed 1.000 over a short span.

What is the best career on-base percentage? Ted Williams, at .482, among players with at least 4,000 at-bats in the historical record.

Which should I read first on a stats page? The triple slash line, then the context, and the guide on how to read a player's statistics page explains every column.

Where to go next

The next step after the three numbers is context. Read OPS and OPS+, then wOBA and wRC+. For what older box scores left out, see what old box scores tell us and what they do not. The site's leaders pages list current and career leaders in each category, and the stats and analytics topic page gathers more reading.