One acre-foot is approximately how many gallons?

• A. 43,560
• B. 325,851
• C. 1,320
• D. 2,000

Answer: (B)

One acre-foot represents the volume needed to cover one acre with one foot of water, so it’s inherently a measure in cubic feet, which then gets converted to gallons. An acre-foot equals 43,560 cubic feet. To turn that into gallons, use 1 cubic foot = 7.48052 gallons. Multiply: 43,560 × 7.48052 ≈ 325,851 gallons. That makes the correct amount about 325,851 gallons. The other numbers don’t match this conversion: 43,560 is the cubic feet in an acre-foot (not gallons), and 2,000 or 1,320 are far off from the gallon total you get after converting the volume. The key is carrying the units through the conversion accurately.