Slugging percentage is total bases divided by AB. A batter gets one total base for a single, two for a double, three for a triple, and four for a homer. You can do this: SLG = Singles + (2*2B) + (3*3B) + (4*HR) / AB But this is easier: SLG = Hits + 2B + (2*3B) + (3*HR) / AB The reason the second one is easier is that most stat pages list total hits but not singles. You're saving yourself the bother of subtracting doubles, triples, and homers from the total number of hits to get singles. Note that the formula for total bases in Brewerfan.net stat glossary is wrong. It'll have to be corrected eventually. I'll quote the Hardball Times Stat Glossary on FIP: While I'm at it, here's xFIP: Russ can explain these stats a whole lot better than I, but the idea is that a pitcher's ERA is affected by defense, and these stats try to eliminated that effect. FIP would be more of an 'expected' ERA.