Pool Volume Calculator
Find how many gallons or litres your pool holds for rectangle, round, oval or kidney shapes with a sloping floor, then the chlorine and salt doses.
The interactive tool loads here when JavaScript runs.
About this toolWhat is the Pool Volume Calculator?
Every pool chemical dose starts with the volume, and most owners only know it roughly. This pool volume calculator works it out from the shape and the water depth at each end, then uses that number to give the dose of chlorine for any common product, the salt for a salt-water chlorinator and how long a hose takes to fill it.
Pick a rectangle, round, oval, oval with straight sides, kidney or a free-form pool with a known surface area. Enter the length and width (or diameter) and the shallow and deep water depths; for a flat floor enter the same depth twice. The result is shown in US gallons, litres, cubic metres and imperial gallons together.
Choose a chlorine product, from 12.5% liquid chlorine to cal-hypo, dichlor or trichlor, and the amount you want to raise free chlorine by. The calculator also flags what stabilised chlorine adds over time: cyanuric acid from dichlor and trichlor and calcium from cal-hypo.
- Rectangle, round, ellipse, straight-sided oval, kidney and free-form shapes
- Sloping floors from shallow and deep depths
- US gallons, litres, cubic metres and imperial gallons at once
- Chlorine dose for liquid, bleach, cal-hypo, dichlor and trichlor, with CYA and calcium side effects
- Salt dose and fill time; everything runs in the browser
How to use the Pool Volume Calculator
- Choose imperial (feet, gallons, ounces, pounds) or metric (metres, litres, grams).
- Pick the pool shape and enter its length and width, its diameter, or for a free-form pool its surface area.
- Enter the water depth at the shallow and deep ends, measured to the waterline, not the top of the wall.
- Choose the chlorine product and how many ppm you want to raise free chlorine by, and the current and target salt levels if you run a salt cell.
- Read the volume, the chlorine dose, the salt to add and the fill time at your hose flow, then copy the result for your pool log.
Worked examples
16 x 32 ft in-ground pool
Input
Rectangle 32 x 16 ft, 3.5 ft shallow, 8 ft deep
Output
2,944 ft³ = 22,023 US gal (83,365 L)
The average depth is 5.75 ft and the surface is 512 ft². Raising free chlorine by 2 ppm takes about 45 fl oz of 12.5% liquid chlorine.
24 ft round above-ground pool
Input
Round, 24 ft diameter, 4 ft of water
Output
About 13,536 US gal
Area is pi x 12² = 452 ft². A pool with 52 inch walls usually holds about 4 ft of water, so use that depth, not the wall height.
Salt for a new salt-water system
Input
22,023 gal, 0 ppm now, 3,200 ppm target
Output
About 588 lb of pool salt, fifteen 40 lb bags
Salt in ppm is milligrams per litre, so 3,200 x 83,365 L = 267 kg. Many chlorinators want 2,700 to 3,400 ppm; follow your cell manual.
Background and insight
Volume is surface area times average depth. For a pool whose floor slopes evenly from the shallow end to the deep end, the average depth is the mean of the two. Hopper-bottom pools with a steep drop into a small deep area hold less than that average suggests, so treat the result as an upper bound for them. One cubic foot holds 7.4805 US gallons and one cubic metre is 1,000 litres.
Ovals come in two kinds. A true ellipse has area pi / 4 x length x width, which is where the trade shortcut of length x width x depth x 5.9 gallons comes from. Many above-ground "oval" pools are really straight-sided with round ends, which hold more; choose that shape for them. Kidney pools use the trade rule of thumb 0.45 x (width at one end + width at the other) x length, which is an approximation.
Chlorine dose is chemistry, not a chart. One part per million is one milligram per litre, so raising 10,000 US gallons (37,854 litres) by 1 ppm takes 37.9 grams of available chlorine. Liquid chlorine sold at 12.5 trade percent holds 125 grams of available chlorine per litre, which works out to about 10.2 fluid ounces. Cal-hypo at 65% needs about 2 ounces by weight. The side effects follow molar ratios: every 1 ppm of chlorine from trichlor adds about 0.6 ppm of cyanuric acid, from dichlor about 0.9 ppm, and from cal-hypo about 0.7 ppm of calcium hardness.
Common use cases
Opening and shocking
Dose chlorine by the ppm you need instead of by a bottle label written for a different pool size.
Salt cell start-up
Work out how many bags of salt bring the water to the chlorinator range.
Buying a pump or heater
Pumps are sized by turnover time and heaters by volume, so both start from gallons.
Filling or topping up
Estimate how long the hose needs to run and what the water bill will cover.
Tips and limitations
- Add liquid chlorine in front of a return jet with the pump running, and test again after the water has circulated.
- Liquid chlorine and bleach lose strength in storage, especially when warm. Old product needs more than the calculator says.
- Trichlor tablets and dichlor raise cyanuric acid with every dose; test CYA regularly and switch to unstabilised chlorine when it is high.
- Never mix different chlorine products, or chlorine and acid, in the same container.
- Measure depth at the waterline; a few inches lower than the wall top makes a real difference on a big pool.
Frequently asked questions
How many gallons are in a 16 x 32 pool?
With a 3.5 ft shallow end and an 8 ft deep end the average depth is 5.75 ft, so 16 x 32 x 5.75 = 2,944 ft³, or about 22,000 US gallons. With a flat 4 ft depth it would be about 15,300 gallons.
How do I calculate pool volume with a shallow and deep end?
Average the two depths and multiply by the surface area. For a rectangle that is length x width x (shallow + deep) / 2 in cubic feet, then multiply by 7.48 for US gallons. Pools with a short, steep hopper hold less than this.
How much liquid chlorine raises a pool by 1 ppm?
About 10 fluid ounces of 12.5% liquid chlorine per 10,000 US gallons, or about 13 ounces of 10% chlorine. Household bleach around 6% takes roughly twice the 12.5% amount.
How much cal-hypo do I need per 10,000 gallons?
About 2 ounces by weight of 65% calcium hypochlorite raises 10,000 gallons by 1 ppm. Each ppm of chlorine from cal-hypo also adds about 0.7 ppm of calcium hardness.
How much salt does a salt-water pool need?
Pounds of salt = ppm increase x gallons x 8.34 / 1,000,000. Taking 20,000 gallons from zero to 3,200 ppm needs about 534 lb. Check the range your chlorinator manual gives before adding salt; it is easier to add more than to remove it.
How do I work out the volume of a kidney-shaped pool?
The trade rule is 0.45 x (width at one end + width at the other) x length x average depth, in cubic feet, then times 7.48 for gallons. It is an approximation; a free-form pool with a known surface area is more accurate.
How long does it take to fill a pool with a garden hose?
Divide the volume by the hose flow. At 10 gallons per minute a 20,000 gallon pool takes about 33 hours. Measure your flow by timing how long the hose takes to fill a 5 gallon bucket.
Is there an in-depth guide to the Pool Volume Calculator?
Yes. “Pool Volume and Chlorine Dosing: Gallons, ppm and Salt” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
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