Pool Volume Calculator

About This Tool

Knowing your pool's exact volume in gallons is essential for proper maintenance, chemical dosing, equipment sizing, and cost estimation. Add too much chlorine to an overestimated pool and you waste money. Underestimate the volume and chemical treatments become too diluted to be effective. This calculator supports four pool shapes and both constant and variable depth configurations to give you an accurate volume measurement.

Pool Volume Formulas

The basic formula for any pool is surface area multiplied by average depth, then converted to gallons. For rectangular pools: Length x Width x Average Depth x 7.48 = gallons. For circular pools: pi x radius² x Average Depth x 7.48 = gallons. For oval pools: pi x (Length/2) x (Width/2) x Average Depth x 7.48 = gallons. For irregular or freeform pools, you need the total surface area (which can be measured by breaking the shape into simpler sections) multiplied by average depth x 7.48.

Calculating Average Depth

Most residential pools have a variable depth with a shallow end and a deep end. The simplest method is to add the shallow end depth and deep end depth, then divide by two. For a pool with a 3.5-foot shallow end and an 8-foot deep end, the average depth is (3.5 + 8) / 2 = 5.75 feet. This works well for pools with a gradual slope. For pools with a distinct hopper bottom (flat shallow area, steep drop, flat deep area), you may need to calculate each section separately for greater accuracy.

Why Pool Volume Matters

Chemical dosing: Every pool chemical — chlorine, pH adjuster, algaecide, stabilizer, shock treatment — is dosed per 10,000 gallons. Using the wrong volume leads to over- or under-treatment. Over-chlorination causes skin and eye irritation and damages pool equipment. Under-chlorination allows algae and bacteria growth. Equipment sizing: Your pump and filter must be sized to turn over the entire pool volume in 6-8 hours. A pool with 20,000 gallons needs a pump that moves at least 2,500-3,333 gallons per hour (42-56 GPM). Heater sizing: Pool heaters are rated in BTU; the time to heat your pool depends directly on volume.

Common Pool Sizes and Volumes

A small residential pool (12x24 ft, 3.5-5 ft depth) holds about 7,600 gallons. A medium pool (16x32 ft, 3.5-6 ft depth) holds about 18,000 gallons. A large pool (20x40 ft, 3.5-8 ft depth) holds about 34,300 gallons. An Olympic-size pool (164x82 ft, 6.5 ft depth) holds about 660,000 gallons. Round above-ground pools are common in the 12-foot (2,700 gal), 15-foot (4,600 gal), 18-foot (7,600 gal), and 24-foot (13,500 gal) diameters at 4 feet deep.

Filling Your Pool

A standard garden hose delivers about 5-10 gallons per minute, or 300-600 gallons per hour. Filling a 20,000-gallon pool from a garden hose takes roughly 33-67 hours (1.5-3 days of continuous running). Many pool owners use a water delivery service for the initial fill, which can bring 4,000-6,000 gallons per truckload. Water costs for filling vary widely: municipal water at $0.004-$0.01 per gallon means a 20,000-gallon fill costs $80-$200. Water delivery trucks typically charge $200-$400 per load.

Using Volume for Chemical Calculations

Once you know your pool volume, chemical dosing becomes straightforward. To raise free chlorine by 1 ppm, add 0.00013 ounces of liquid chlorine (12.5% sodium hypochlorite) per gallon of pool water. For a 20,000-gallon pool, that's about 2.6 ounces or 10 ounces of standard pool shock (cal-hypo). To raise pH by 0.1, add about 6 ounces of soda ash per 10,000 gallons. Pool supply stores and apps can calculate exact doses once you input your volume — but the volume must be accurate for the math to work.