Summarize:

Also called slugging average, SA, or SLG, this is a player's average number of bases per bat. If a player has an (unrealistic) slugging percentage of 1, their average result was a single. This only measures number of bases from hits, not from walks or hit by pitch. Ignoring the bases out of the batter's control makes this a more accurate measure of offensive power. Most player stats don't include singles, but it's easy to figure out from other stats. First, add Home Runs + Triples + Doubles to get all the hits that aren't singles. Then subtract your answer from the total number of Hits to get the number of Singles. For example, Willie McCovey has career stats of 521 Home Runs, 46 Triples, and 353 Doubles, adding up to 920. Subtract 920 from his career Hits of 2211 to get the number of Singles: 1291. Add together (Singles) + (2 x Doubles) + (3 x Triples) + (4 x Home Runs) to get the total number of bases. Willie McCovey scored a total number of bases equal to (1291) + (2 x 353) + (3 x 46) + (4 x 521) = 1291 + 706 + 138 + 2084 = 4219. Divide total bases by the number of at bats to get the slugging percentage. Willie McCovey had 8197 At Bats, so his career slugging percentage is 4219 ÷ 8197 = 0.5147 (rounded to 0.515). On average, he scored a little more than one base for every two at bats.
Understand slugging percentage. Find the number of singles. Calculate the number of bases. Divide your answer by at bats.