How much volume (in cm3) is gained by a person who gains 11.4 lbs of pure fat?

The density of fat is about 0.9 grams/ml

We may convert this into pounds / cm³

0.9 grams/ml * 1 lb / 454 grams * 1 ml / 1 cm³ = 0.002 lb/cm³

Next, we use the formula:

Density = mass / volume

Volume = mass / density

Volume = 11.4 / 0.002

Volume = 5,700 cm³

The person will have gained 5,700 cm³ of volume