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Barry Bonds holds the MLB record for highest slugging average in a season (.863).

In baseball statistics, slugging average (abbreviated SLG) is the most popular measure of the power of a hitter. It is calculated as total bases divided by at bats.

SLG = (1B + (2 x 2B) + (3 x 3B) + (4 x HR))/ AB , where AB is the number of at-bats for a given player, and 1B, 2B, 3B, and HR are the number of singles, doubles, triples, and home runs, respectively.

For example, in 1920, Babe Ruth was playing his first season for the New York Yankees. In 458 at bats, he had 172 hits, including 73 singles, 36 doubles, 9 triples, and 54 home runs, which brings the total base count to (73 × 1) + (36 × 2) + (9 × 3) + (54 × 4) = 388. He had 458 at bats, so his total number of bases (388) divided by his total at-bats (458) is .847, his slugging average. The next year he slugged .846, and for 80 years those records went unbroken until 2001, when Barry Bonds hit 411 bases in 476 at-bats, bringing his average to .863, unmatched since.

Long after it was first invented, slugging average gained new significance when baseball analysts realized that it combined with on-base percentage (OBP) to form a very good measure of a player's overall offensive production (in fact, OBP + SLG was originally referred to as "production" by baseball writer and statistician Bill James). A predecessor metric was developed by Branch Rickey in 1954. Rickey, in Life Magazine, suggested that combining OBP with what he called "extra base power" (EBP) would give a better indicator of player performance than typical Triple Crown stats. EBP was a predecessor to slugging average.

Allen Barra and George Ignatin were apparently the early adopters in combining the two modern-day statistics, multiplying them together to form what is now known as "SLOB" (Slugging × On-Base). Bill James applied this principle to his Runs Created formula several years later (and perhaps independently), essentially multiplying SLOB × At-Bats (the actual formula for Runs Created is: RC = [(Hits + Walks)(TotalBases)] / [AtBats + Walks]). In 1984, Pete Palmer and John Thorn developed perhaps the most widespread means of combining slugging and on-base average: OPS. "OPS" simply stands for "on-base plus slugging", and is a simple addition of the two values. Because it is easy to calculate, OPS has been used with increased frequency in recent years as a shorthand form to evaluate contributions as a batter.

Slugging average is sometimes referred to as 'Slugging Percentage'. The term slugging percentage is a misnomer, for it is actually a weighted average, not a percentage.

• Citing to Rickey's EBP article