Yeah. And you can approximate many common materials as weighing "close enough" to water, if you're doing back of the envelope calculations. Organisms in general

Yeah. And you can approximate many common materials as weighing "close enough" to water, if you're doing back of the envelope calculations. Organisms in general, food, building materials. Oil is about 90% the density of water. Plastic and wood probably vary from 50% to 130%. Metal and rock are obviously heavier, so throw in a multiplier. It's great because you can just convert grams to milliliters or cubic centimeters (water is 1g/mL) and fudge it as necessary.