Swimming Pool Volume Calculator
Knowing your pool volume is essential for calculating the right amount of chemicals. Works for rectangular, circular, and oval pools.
Pool Volume Calculator
Common Pool Sizes
| Pool Size | Approx Gallons |
|---|---|
| 12×24 ft (4ft deep) | ~8,600 gal |
| 16×32 ft (5ft deep) | ~19,200 gal |
| 18×36 ft (5ft deep) | ~24,300 gal |
How to Calculate Swimming Pool Volume
Every pool volume formula works the same way: find the surface area of the pool, multiply it by the average depth to get cubic feet, then convert cubic feet to gallons. One cubic foot of water holds 7.48 US gallons (28.32 liters).
| Pool Shape | Formula (US gallons) |
|---|---|
| Rectangular | Length x Width x Average Depth x 7.48 |
| Circular | Diameter x Diameter x Average Depth x 5.9 |
| Oval | Length x Width x Average Depth x 6.7 |
| Kidney / freeform | (Widest width + Narrowest width) x 0.45 x Length x Depth x 7.48 |
The circular and oval multipliers already fold in the shape constant, so you do not need to work out pi yourself. For a freeform pool the 0.45 factor is an industry approximation, which is close enough for chemical dosing.
Worked example: a 16 x 32 ft rectangular pool
Say the shallow end is 3 ft and the deep end is 7 ft, so the average depth is 5 ft.
- Surface area: 16 x 32 = 512 sq ft
- Volume in cubic feet: 512 x 5 = 2,560 cu ft
- Volume in gallons: 2,560 x 7.48 = 19,149 US gallons
- Volume in liters: 19,149 x 3.785 = 72,478 liters
How to Find Your Average Depth
Average depth is where most people go wrong, and it is the single number that most affects your result. How you measure it depends on the pool floor.
- Flat-bottom pool: the depth is the average depth. Nothing to calculate.
- Constant slope: add the shallow-end depth to the deep-end depth and divide by 2. A 3 ft to 7 ft pool averages 5 ft.
- Pool with a diving well: a simple two-point average overstates the volume, because the deep section is usually a small part of the total floor. Measure the shallow depth, the depth at the start of the slope, and the deep-end depth, then average all three.
How Much Chlorine Does Your Pool Need?
Pool volume matters because almost every chemical dose is written per 10,000 gallons. Get the volume wrong and every dose you make afterwards is wrong too.
| Goal | Product | Dose per 10,000 gallons |
|---|---|---|
| Raise free chlorine by 1 ppm | Liquid chlorine (12.5%) | About 10 fl oz |
| Shock after heavy use | Cal-hypo (73%) | About 1 lb |
| Raise pH by 0.2 | Soda ash | About 6 oz |
| Lower pH by 0.2 | Muriatic acid | About 12 fl oz |
| Raise alkalinity by 10 ppm | Baking soda | About 1.5 lb |
Always follow the dose printed on your own product label, since concentrations vary between brands. Treat the table above as a sanity check on the order of magnitude, and add chemicals in stages, retesting between doses.
Common Pool Volume Mistakes
- Using the deep-end depth for the whole pool. This is the most common error and it can overstate volume by 30 percent or more, leading to chronic over-chlorination.
- Measuring in mixed units. Keep everything in feet before converting. Mixing feet and inches without converting first quietly wrecks the result.
- Forgetting attached spas and tanning ledges. A spillover spa can add 500 to 1,000 gallons that your chemical dosing has to account for.
- Reusing the builder’s number after a resurface. A new liner or plaster job changes interior dimensions slightly. Re-measure rather than trusting a decade-old figure.
Frequently Asked Questions
How do I find average pool depth?
Add the shallow end and deep end depths together and divide by 2. Example: (3 ft + 7 ft) / 2 = 5 ft average depth. If your pool has a diving well rather than a constant slope, also measure the depth where the slope begins and average all three readings, because a simple two-point average will overstate the volume.
Why does knowing my pool volume matter?
Pool volume determines how much chlorine, algaecide, pH adjuster and shock you need. Almost every pool chemical is dosed per 10,000 gallons, so if your volume figure is wrong then every dose you calculate from it is wrong too, which leads to either unsafe water or wasted chemicals.
How many gallons is a standard 16×32 ft pool?
A 16 x 32 ft rectangular pool with an average depth of 5 ft holds about 19,150 US gallons, or roughly 72,500 liters. The exact figure depends on your average depth: the same pool at a 4 ft average depth holds about 15,300 gallons.
How do I convert pool gallons to liters?
Multiply US gallons by 3.785 to get liters. For example, 20,000 US gallons equals about 75,700 liters. To convert the other way, multiply liters by 0.264.
Does an above-ground pool use the same formula?
Yes. An above-ground pool uses exactly the same formula as an in-ground pool of the same shape. Above-ground pools are usually flat-bottomed, which actually makes the calculation easier because the water depth is the average depth. Just remember to measure to the water line and not to the top rail.
How accurate does my pool volume need to be?
For routine chemical dosing, within about 5 percent is fine. Being off by a few hundred gallons on a 20,000 gallon pool will not change your chlorine dose meaningfully. Being off by 30 percent, which happens when people use the deep-end depth for the whole pool, absolutely will.