What is the density of water?

• A. 1000
• B. 62.4
• C. 8.34
• D. 2.7

Answer: (B)

Density is mass per unit volume, so to compare water’s density you need to pick a unit system. Water is about 1 gram per cubic centimeter, which is 1000 kilograms per cubic meter in SI units. In imperial units, one cubic foot of water weighs about 62.4 pounds, so the density is 62.4 lb per cubic foot. The other numbers correspond to different unit choices: 1000 (kg/m^3) is the SI value, 8.34 (lb/gal) is pounds per gallon, and 2.7 is the density of aluminum in g/cm^3. Since the given option uses the imperial, pound-per-cubic-foot form, 62.4 is the best match.