Pool Volume Calculator NZ
Almost every decision you make about a swimming pool depends on knowing how much water is in it. Chlorine, salt, acid, algaecide, flocculant and stabiliser are all dosed per thousand litres, and a heat pump is sized against the volume it has to warm. Guess the volume and you either underdose, which does nothing, or overdose, which costs money and can damage the pool surface. This calculator gives you the number the dosing instructions are asking for. Choose the shape of your pool, enter its length and width, then enter the depth at the shallow end and at the deep end. The calculator averages the two depths, works out the surface area from the shape, and multiplies them to give the volume in litres, in cubic metres and as a weight in tonnes. It assumes a floor that slopes evenly from one end to the other, which is how most residential pools are built. If your pool has a flat floor, put the same figure in both depth boxes.
Assumes the floor slopes evenly between the two depths you enter. For a flat-bottomed pool, enter the same depth twice. Steps, benches and a swim-out reduce the real volume by a small amount, usually under 3 per cent.
How it works
Volume is surface area multiplied by average depth. The average depth of an evenly sloping floor is the shallow depth plus the deep depth, divided by two.
Surface area depends on the shape. A rectangular pool is length multiplied by width. A round pool is pi multiplied by the radius squared, where the radius is half the diameter you entered in the length box. An oval pool is pi multiplied by half the length multiplied by half the width.
One cubic metre of water is exactly 1,000 litres, so the conversion to litres is a multiplication by a thousand. Fresh water weighs almost exactly one tonne per cubic metre, which is why the volume in cubic metres and the weight in tonnes are the same figure. That weight matters if you are building a pool on a deck or a suspended slab.
Worked example
A rectangular pool 8 m long and 4 m wide, 1.1 m deep at the shallow end and 1.8 m at the deep end.
The average depth is (1.1 + 1.8) divided by 2, which is 1.45 m. The surface area is 8 multiplied by 4, which is 32 m2. The volume is 32 multiplied by 1.45, which is 46.4 m3, or 46,400 litres. The water alone weighs about 46.4 tonnes.
That figure is what you dose against. A product calling for 10 g per 1,000 litres needs 464 g for this pool, not the 400 g you would use if you had rounded the volume down to a tidy 40,000 litres.
Related calculators
- Pool Salt Calculator: how many kilograms of salt to add once you know the volume.
- Pool Running Cost Calculator: what the pool costs to run each year.
- Pool Build Cost Calculator: what a new pool costs to put in the ground.
- Spa Pool Running Cost Calculator: the same question for a spa rather than a pool.
- Cylinder Volume Calculator: volume of a round tank in cubic metres and litres.