Swimming Pool Water Calculator
Find out how many gallons your swimming pool holds and how much water evaporates monthly. Use it when filling a new pool, budgeting for water costs, or planning seasonal top-offs.
About this calculator
Pool volume depends on shape. For a rectangular pool: Volume (gal) = length × width × depth × 7.48, where 7.48 converts cubic feet to gallons. For a round pool: Volume = π × (diameter/2)² × depth × 7.48. For an oval pool: Volume = π × (length/2) × (width/2) × depth × 7.48. Monthly evaporation loss is calculated the same way but substitutes the evaporation depth (in feet, converted from inches by dividing by 12) for the pool depth. Total water need = initial fill volume + monthly evaporation volume. Evaporation rates vary by climate — hot, dry, and windy locations can lose 1–2 inches per week. The 7.48 factor is exact: one cubic foot holds 7.48052 U.S. gallons.
How to use
Say you have a rectangular pool 20 ft long, 10 ft wide, and 5 ft deep, with 0.5 inches of monthly evaporation. Fill volume: 20 × 10 × 5 × 7.48 = 7,480 gallons. Evaporation loss: 20 × 10 × (0.5/12) × 7.48 = 20 × 10 × 0.0417 × 7.48 ≈ 62.3 gallons per month. Total first-month water requirement: 7,480 + 62.3 ≈ 7,542 gallons. At a typical residential water rate of $0.005 per gallon, that's about $37.70 to fill and maintain the pool for the first month.
Frequently asked questions
How many gallons of water does an average residential swimming pool hold?
Most backyard rectangular pools range from 10,000 to 30,000 gallons depending on size and depth. A common 16 × 32 ft pool with an average depth of 5 feet holds approximately 19,200 gallons. Above-ground round pools are typically smaller, ranging from 1,000 to 5,000 gallons. Knowing your pool's volume is essential for correctly dosing chemicals.
How much water does a swimming pool lose to evaporation each month?
Evaporation losses vary widely based on climate, temperature, humidity, wind, and whether the pool is covered. In hot, arid regions pools can lose 1–2 inches of water per week, translating to 500–1,000+ gallons monthly for a mid-sized pool. A solar or safety cover can cut evaporation by up to 95%, dramatically reducing refill costs and chemical consumption.
How long does it take to fill a swimming pool with a garden hose?
A standard garden hose delivers about 8–10 gallons per minute. To fill a 20,000-gallon pool, you'd need approximately 2,000–2,500 minutes, or 33–42 hours of continuous flow. Many homeowners use two hoses or arrange a bulk water delivery to reduce fill time. Always check with your local utility first, as some municipalities restrict large single-day draws.