ABC Tools

Batting Average and OPS, Explained

After reading this you can turn any standard batting line into AVG, OBP, SLG and OPS by hand, and you will know what a given number says about the hitter.

Four numbers dominate how a hitter is described: batting average, on-base percentage, slugging percentage and OPS. They come from the same box-score line, but they answer different questions. Batting average asks how often you get a hit. On-base percentage asks how often you avoid making an out. Slugging asks how many bases you take per swing that counts. OPS glues the last two together.

Here is the hook. Two hitters both bat .280. One walks 30 times a year, the other walks 80. Over a full season the second hitter reaches base roughly 50 more times without a single extra hit. Batting average cannot see that difference. OBP can, and that is why the other three numbers exist.

What each statistic measures

Batting average (AVG)
Hits divided by at-bats. The oldest headline stat. It ignores walks entirely.
On-base percentage (OBP)
How often you reach base per plate appearance, counting hits, walks and hit-by-pitches.
Slugging percentage (SLG)
Total bases per at-bat. A home run is worth four times a single here, so power shows up.
OPS
On-base plus slugging. A single number that correlates strongly with runs scored.

The key split is the denominator. AVG and SLG divide by at-bats. OBP divides by plate appearances. At-bats exclude walks, hit-by-pitches and sacrifices. Plate appearances include them. That is not an accident: a walk is not a failure at bat, so OBP refuses to punish it, while AVG never sees it at all.

When to use each, and when not to

Use AVG when you only want contact rate: how often a swing turns into a hit. It is easy to read and easy to compare across eras, but it treats a solo home run and an infield single as equal, and it pretends a walk never happened.

Use OBP when you care about outs. A team gets 27 outs per game and no more. A hitter who avoids outs, by any means, keeps the line moving. OBP is the single best simple predictor of runs among these four.

Use SLG for power, and OPS when you want one number that respects both getting on base and hitting for extra bases. Do not use OPS to compare a first baseman with a shortstop and stop there: it says nothing about defense, baserunning or position. It is a hitting summary, not a player rating.

OPS adds two fractions with different denominators, so it is not a true probability or rate. A value of .900 does not mean 90 percent of anything. Treat it as an index, useful for ranking hitters, not as a percentage.

The formulas

Batting average is the simplest ratio in the sport.

\text{AVG} = \frac{H}{AB}

Here H is hits and AB is at-bats. A hit is a single, double, triple or home run that lets you reach base safely without an error or fielder's choice.

On-base percentage counts every safe arrival and divides by every trip to the plate that ends in a decision.

\text{OBP} = \frac{H + BB + HBP}{AB + BB + HBP + SF}

The numerator adds walks (BB) and hit-by-pitches (HBP) to hits. The denominator adds those same events plus sacrifice flies (SF) to at-bats. Sacrifice flies sit in the denominator but not the numerator, so a sac fly counts against your OBP even though it drove in a run. Sacrifice bunts are left out of the standard formula entirely.

Slugging weights each hit by the bases it produces.

\text{SLG} = \frac{(1B) + 2(2B) + 3(3B) + 4(HR)}{AB}

A single (1B) is one base, a double two, a triple three, a home run four. Because singles are the leftover, compute them as 1B = H - 2B - 3B - HR. The numerator is called total bases.

OPS is just a sum.

\text{OPS} = \text{OBP} + \text{SLG}

A worked example with the demo line

From box score to four numbers

Use the tool's default line: AB = 550, H = 155, 2B = 32, 3B = 3, HR = 24, BB = 60, HBP = 5, SF = 4.

  1. Batting average: 155 / 550 = 0.28182, which rounds to .282.
  2. Count singles: 155 - 32 - 3 - 24 = 96 singles.
  3. Total bases: 96 + 2(32) + 3(3) + 4(24) = 96 + 64 + 9 + 96 = 265.
  4. Slugging: 265 / 550 = 0.48182, which rounds to .482.
  5. OBP numerator: 155 + 60 + 5 = 220 times on base.
  6. OBP denominator: 550 + 60 + 5 + 4 = 619 plate appearances that count.
  7. On-base percentage: 220 / 619 = 0.35541, which rounds to .355.
  8. OPS: 0.355 + 0.482 = 0.837, reported as .837.

So this hitter reads .282 / .355 / .482, OPS .837. The three-slash line is the standard shorthand, always in that order: AVG, OBP, SLG.

Notice the gaps. The 60 walks lift OBP well above AVG: the difference is .355 - .282 = .073, close to a typical full-time hitter's gap. The 24 home runs and 32 doubles push SLG to .482, a full .200 above the average, which is the signature of real power.

Reading the numbers in league context

Raw numbers mean nothing without a scale. The table below gives rough tiers for a modern MLB regular. These shift year to year with the run environment, so treat them as a compass, not a ruler.

Approximate quality tiers for a full-time MLB hitter
TierAVGOBPSLGOPS
Elite.310.400.560.950
Very good.290.365.500.865
League average.250.320.410.730
Below average.230.295.370.665
Replacement.215.275.340.615

The demo hitter's OPS of .837 lands between very good and average, closer to very good. A useful shortcut: an OPS near .900 is All-Star territory, .800 is a solid regular, .700 is a fringe starter, and below .650 the bat is a liability.

The four outputs for the default line. Note OPS towers over the others because it is a sum, not a rate.

How walks reshape the line

The most instructive move is to hold everything constant and change only the walk total. Walks never touch AVG or SLG, because they are outside the at-bat count. They lift OBP, and therefore OPS, straight up.

Starting from the demo line (AVG .282, SLG .482), changing walks alone: at 20 walks OBP is 171/579 = .295 and OPS is .777; at 60 walks OBP is .355 and OPS is .837; at 100 walks OBP is 259/659 = .393 and OPS is .875. Each extra 40 walks adds roughly .05 to OPS with no change in batting average.

Common mistakes

Several errors show up again and again when people compute these by hand.

  • Putting walks in the AVG denominator. At-bats already exclude walks. Dividing hits by plate appearances gives a number that is not batting average and not OBP.
  • Forgetting that doubles, triples and home runs are already in the hit total. If you add them to hits when finding singles, you double count. Singles are H - 2B - 3B - HR, never H + 2B + 3B + HR.
  • Leaving sacrifice flies out of the OBP denominator. A sac fly is a plate appearance that ends in an out at the plate for OBP purposes, so it belongs in the bottom of the fraction.
  • Reading OPS as a percentage. It is a sum of two ratios and can exceed 1.000. A .900 OPS is not "90 percent."
  • Comparing across eras without adjustment. A .800 OPS in a low-scoring season is worth more than the same .800 in a high-scoring one. For cross-era work you want OPS+, which normalizes to the league.

Sanity check your slugging with a range. SLG can never be below AVG, and it caps at 4.000 (a home run every at-bat). If your SLG comes out under your AVG, you have miscounted total bases.

Related tools

If you also track the pitching side, the ERA and WHIP Calculator is the mirror image of this page. To turn runs scored and allowed into an expected win total, use the Pythagorean Expectation Calculator. For efficiency stats in other sports, the True Shooting % Calculator handles basketball and the Passer Rating Calculator handles NFL quarterbacks. Cricket fans can compare run-scoring rates with the Cricket Run Rate Calculator.

Frequently asked questions

Why is on-base percentage always higher than batting average?

Because OBP adds walks and hit-by-pitches to the numerator while its denominator grows by roughly the same amount. Any hitter who draws even one walk will have OBP above AVG. In the demo line the gap is .073, from 60 walks and 5 hit-by-pitches.

Can slugging percentage be over 1.000?

Yes. SLG is total bases per at-bat, and total bases can exceed at-bats. A hitter with 2 doubles and a home run in 4 at-bats has (2 + 2 + 4) / 4 = 2.000 slugging for that stretch. Over a full season it settles below .700 for even the best power hitters.

What is a good OPS?

For a full-time MLB hitter, .800 is a solid regular, .900 is All-Star level and 1.000 is an MVP-caliber season. The demo line's .837 is a good everyday player, above average but not elite.

Do sacrifice bunts affect these numbers?

Not in the standard formulas here. Sacrifice bunts are excluded from at-bats and from the OBP denominator, so they leave all four statistics untouched. Only sacrifice flies enter, and only in the OBP denominator.

Why do statisticians dislike OPS?

Because it adds two fractions with different denominators, which is not mathematically clean. It also weights on-base and slugging equally, when getting on base is actually worth a bit more for scoring runs. Despite that, OPS tracks team run creation well enough that it stuck. For a cleaner measure, analysts use weighted on-base average (wOBA) instead.

These four numbers are estimates for study and comparison, not a full player evaluation and not coaching or medical advice. Feed a real box-score line into the calculator, check the arithmetic against the worked example above, and you will read any hitter's slash line with confidence.

Try it yourself in the tool

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