Excess Body Weight is basically your weight minus your ideal body weight. There are a few different formulas for calculating "ideal body weight," but for the most part they rely on some variation of height, gender, and age. Here are some example formulas (sorry its in Kg not pounds).
G. J. Hamwi Formula (1964)
Male: 48.0 kg + 2.7 kg per inch over 5 feet
Female: 45.5 kg + 2.2 kg per inch over 5 feet
Invented for medicinal dosage purposes.
B. J. Devine Formula (1974)
Male: 50.0 + 2.3 kg per inch over 5 feet
Female: 45.5 + 2.3 kg per inch over 5 feet
Similar to the Hamwi Formula, it was originally intended as a basis for medicinal dosages based on weight and height. Over time, the formula became a universal determinant of IBW.
J. D. Robinson Formula (1983)
Male: 52 kg + 1.9 kg per inch over 5 feet
Female: 49 kg + 1.7 kg per inch over 5 feet
Modification of the Devine Formula.
D. R. Miller Formula (1983)
Male: 56.2 kg + 1.41 kg per inch over 5 feet
Female: 53.1 kg + 1.36 kg per inch over 5 feet