Pool volume calculator
Every chemical dose depends on how much water you're treating, so this is the number to get right first. Pick your pool's shape, enter its size, and the calculator gives the volume in US gallons and liters, plus the water's surface area.
Use this volume in: salt · chlorine · shock · pH · alkalinity · calcium · stabilizer · pump turnover · heater size
How to measure your pool
- Measure the water, not the pool. Use the inside dimensions, and measure depth from the floor to the water line, not to the top of the wall. On an above-ground pool, the water usually sits several inches below the top rail.
- Sloped floors: enter the shallow-end and deep-end water depths. The calculator uses the average of the two, which works well for a floor that slopes evenly. If your pool has a long flat shallow area and a short, steep deep "hopper", measure a few points and use a weighted average instead.
- Round pools: measure the diameter straight across the middle.
- Kidney and freeform pools: measure the overall length and the width at the narrowest and widest points. The 0.45 factor is a long-standing approximation for this shape, so treat the answer as a close estimate.
The formulas
Round: 3.1416 × (diameter ÷ 2)² × average depth × 7.48
Oval: 3.1416 × (length ÷ 2) × (width ÷ 2) × average depth × 7.48
Kidney: 0.45 × (narrow width + wide width) × length × average depth × 7.48
Average depth = (shallow depth + deep depth) ÷ 2
Each formula finds the surface area, multiplies by the average depth to get cubic feet, and converts to US gallons. One cubic foot holds 7.48 gallons. In metric, length × width × depth in meters gives cubic meters, and each cubic meter is 1,000 liters. One US gallon is 3.785 liters.
Worked examples
A 16 × 32 ft in-ground pool, 3.5 to 8 ft deep
Average depth: (3.5 + 8) ÷ 2 = 5.75 ft. Surface area: 16 × 32 = 512 sq ft. Volume: 512 × 5.75 = 2,944 cubic feet × 7.48 ≈ 22,000 gallons (about 83,400 liters).
A 24 ft round above-ground pool with 4.5 ft of water
Radius 12 ft, so the area is 3.1416 × 12 × 12 ≈ 452 sq ft. 452 × 4.5 ≈ 2,036 cubic feet × 7.48 ≈ 15,200 gallons.
A kidney pool, 30 ft long, 10 and 16 ft wide, 5 ft average depth
Area: 0.45 × (10 + 16) × 30 = 351 sq ft. 351 × 5 = 1,755 cubic feet × 7.48 ≈ 13,100 gallons.
Typical pool volumes
| Pool | Water depth | Approx. volume |
|---|---|---|
| 15 ft round above-ground | 4 ft | 5,300 gal |
| 18 ft round above-ground | 4 ft | 7,600 gal |
| 24 ft round above-ground | 4.5 ft | 15,200 gal |
| 15 × 30 ft oval above-ground | 4 ft | 10,600 gal |
| 14 × 28 ft in-ground | 3.5–6 ft | 13,900 gal |
| 16 × 32 ft in-ground | 3.5–8 ft | 22,000 gal |
| 20 × 40 ft in-ground | 3.5–8 ft | 34,400 gal |
These are worked from the formulas above. Your own measurements will give a better number.
Checking the volume another way
If you fill the pool from a hose or a municipal supply with a meter, the water bill or meter reading before and after filling gives the volume directly. You can also time how long the hose takes to fill a 5-gallon bucket, then multiply by the total fill time. Another check: if a measured dose of salt or stabilizer raises the test reading much more or less than the calculators predict, your volume estimate is probably off.
Frequently asked questions
How many gallons are in my pool if I only know the length and width?
You also need the depth. As a rough guide for a typical in-ground pool with an average depth of about 5 ft, multiply length × width × 5 × 7.48. For a 16 × 32 ft pool that's about 19,100 gallons.
Why does the volume matter so much?
Every dose is "so much per 10,000 gallons". If you overestimate your volume by 30%, you'll add 30% too much of everything, which wastes chemicals and can push the water out of balance. If you underestimate, the doses won't do their job.
Should I use the volume before or after topping up?
Use the volume at your normal water level. A few inches of difference in level changes the total by only a few percent.