Backyard Calc Hub

Pool Volume Calculator

Pick your pool's shape, enter its size and water depth, and see how many gallons or litres it holds. You need this number for every chlorine, salt and pH dose.

Units
Shape and size
Water depth
Shallow end
ftin
Deep end
ftin

Measure the depth of the water, not the height of the pool wall.

Allow for steps or sloping sides (optional)

Both are rough rules of thumb. Leave them off if they don't fit your pool.

Fill time (optional)
Measure your hose flow with a bucket

Turn the tap on fully, time how long the bucket takes to fill, and type it here. The flow box fills in for you.

Why your pool's volume matters

Every chemical dose is worked out from how much water the pool holds: chlorine, salt, pH adjusters and stabilizer alike. Hayward's and Pentair's salt chlorinator manuals, for example, both have you look up how much salt to add in a chart of pool gallons. If your volume is 20% out, every dose you work out from it is 20% out too.

Once you have the number, use it in the pool chlorine calculator, the pool salt calculator and the pool drain & refill calculator.

How the calculation works

Volume = water surface area × average depth. The surface area depends on the shape:

Worked example

A 32 × 16 ft pool is 3 ft 6 in deep at the shallow end and 6 ft 6 in at the deep end.

In metric, an 8 × 4 m pool that goes from 120 cm to 180 cm deep has an average depth of 1.5 m: 32 m² × 1.5 m = 48 m³, or 48,000 litres (12,680 US gallons or 10,559 imperial gallons). Each centimetre of depth holds 320 litres.

Measuring your pool

Pools with a deep hopper

Averaging the two ends assumes the floor slopes evenly. Some in-ground pools instead have a long flat shallow area and then drop steeply into a small deep end, often called a hopper. If most of your pool is close to the shallow depth, it holds less than the average of the two ends suggests. For a closer figure, split the pool along its length into sections (the shallow area, the slope and the deep end), work out each section with its own average depth, and add them up. Pentair's manual also suggests multiplying by 0.85 for pools with sloping sides; you can turn this on under "Allow for steps or sloping sides".

Oval pools: the sources disagree

Pentair's and Hayward's manuals give length × width × average depth × 6.7 for an oval pool (× 893 in metric, for litres from metres). That figure matches an oval with straight sides that is twice as long as it is wide (6.68 before rounding). A true ellipse covers less, π/4 of its length × width, so its multiplier is 5.875: the same as the manuals' 5.9 for a round pool, which is an ellipse whose length and width are equal. Sacramento County's sheet uses the ellipse formula. Rather than pick one number, the calculator lets you choose the shape: if your pool's long sides are straight, pick "Oval with straight sides".

The same manuals round 7.48 up to 7.5 for rectangles and 5.875 up to 5.9 for round pools, so their answers come out about 0.3% and 0.4% higher than the exact maths, which is too small to matter.

Allowances for steps and sloping sides

Sacramento County's operator sheet multiplies a pool's volume by 0.95 to account for steps, so a 19,150-gallon pool becomes 18,193 gallons. Pentair's manual multiplies by 0.85 for pools with sloping sides. Both are rough rules of thumb, which is why they are off unless you tick them.

How long will it take to fill?

Fill time is the volume divided by your hose's flow rate. To find the flow, time how long the hose takes to fill a bucket: flow per minute = bucket size ÷ seconds × 60. A 5-gallon bucket that fills in 30 seconds means 10 gallons a minute, so the 19,150-gallon pool above takes 1,915 minutes: 31 hours 55 minutes. In metric, a 10 litre bucket that fills in 20 seconds means 30 L/min, and 48,000 litres takes 26 hours 40 minutes.

Common questions

How many gallons are in a 16 × 32 ft pool?
It depends on the depth. Going from 3 ft 6 in at the shallow end to 6 ft 6 in at the deep end (an average of 5 ft), a 16 × 32 ft pool holds 19,150 US gallons. Each extra foot of average depth adds 3,830 gallons, and each inch of water is 319 gallons.
Should I use the wall height for an above-ground pool?
No, use the depth of the water. Intex lists its 12 ft × 30 in Easy Set pool with 23 inches of water. At that depth the formula gives 1,622 gallons, but at the full 30 inches it gives 2,115 gallons, about 30% too much. If the maker lists a capacity for your model (Intex gives 1,485 gallons for this one), use the maker's figure.
How accurate is the kidney pool formula?
It is an estimate. Sacramento County's guidance for pool operators gives the area as (A + B) × length × 0.45, where A and B are the widths across each end. A kidney pool 30 ft long and 15 ft and 10 ft across its ends covers about 337.5 sq ft, so at an average depth of 5 ft it holds 12,623 gallons. Imperial County's pool plan form uses the average of the two widths instead of their sum, which halves the area to 168.75 sq ft. That is smaller than a true oval 30 ft long and only 10 ft wide (236 sq ft), so the calculator uses the Sacramento version. If you know the real surface area, choose Freeform and enter it.
What is the difference between US and imperial gallons?
A US gallon is 3.785 litres and an imperial (UK) gallon is 4.546 litres, so the imperial gallon is about 20% bigger. If a product label or equipment manual gives a dose per gallon, check which gallon it means. In metric mode the calculator shows both.
How long does it take to fill a pool with a hose?
Time how long your hose takes to fill a bucket. A 5-gallon bucket that fills in 30 seconds means 10 gallons a minute, so a 19,150-gallon pool takes 1,915 minutes, or 31 hours 55 minutes. Topping up one inch of a 16 × 32 ft pool (319 gallons) takes about 32 minutes at the same flow.

Sources

Last checked and updated: .