How do you figure out a pitchers ERA and players On Base Percentage?

Answer 1

ERA = earned runs / innings pitched *9

OBP = hits +walks +HBP / AB + walks + HBP + sac flies

The links below will give you all of this and much, much more in the way of basic baseball info.

Answer 2

For Era, multiply the number of earned runs allowed by the pitcher times nine then divide by the number of innings the pitcher actually pitched in. Ex. A pitcher who gave up 4 runs in 18 innings would have an ERA of 2.00 (4 x 9/ 18)

To determine the On Base Percentage, divide the total number of times a player safely reached base (by hit, walk, or hit by pitch) by the total number of plate appearances.
Ex. A player gets 25 hits in 75 official at bats (only times when a player either got a hit or recorded an out counts as an "official" at bat for batting avg. purposes), is walked 9 times, and hit by pitch once. So, add hits, walks, and HBP (25+9+1=35); divide that by the sum of the number of official at bats, walks, and HBP (75+9+1=85) That gives you 35/85= .412 On Base Percentage (OBP).

Answer 3

To be algebraically correct,

OBP = (hits + walks + HBP) / (AB + walks + HBP + sac flies)

By convention, ERA is listed to two decimals, OBP to three.