Calculate the specific gravity of a substance with density 64 lb/ft^3 when the density of water is 62.4 lb/ft^3.

• A. 1.00
• B. 1.05
• C. 1.10
• D. 1.03

Answer: (D)

Specific gravity is the ratio of a material’s density to the density of water under the same conditions, so it is a unitless number. Using ρ = 64 lb/ft^3 and ρ_water = 62.4 lb/ft^3, SG = 64 / 62.4 = 1.0256. Rounded to two decimals, that’s about 1.03. The substance is slightly denser than water since SG > 1. The other values are either exactly 1.00 (equal density) or farther rounded from the exact ratio, with 1.03 being the closest match.