Pool Size and Volume: How Many Litres Does Your Pool Hold?
- 4 hours ago
- 7 min read
Ask ten pool owners how many litres their pool holds and nine will guess. It rarely matters until the day it does: a water test comes back low and you need to know how much chlorine to add, a pump fails and you need the right replacement, the council announces a restriction, or a liner replacement means the pool comes back empty and has to be filled again.
Every one of those decisions runs off a single number. This guide gets you that number, then shows you what to do with it.
Start here — common New Zealand pool sizes
Most NZ residential inground pools sit in a narrow band. Find yours below for a working figure, or measure properly using the three steps that follow.
Pool size (L × W) | Avg depth 1.4m | Avg depth 1.5m | Avg depth 1.6m |
8m × 4m | 44,800 L | 48,000 L | 51,200 L |
9m × 4m | 50,400 L | 54,000 L | 57,600 L |
10m × 4m | 56,000 L | 60,000 L | 64,000 L |
10m × 5m | 70,000 L | 75,000 L | 80,000 L |
11m × 5m | 77,000 L | 82,500 L | 88,000 L |
12m × 5m | 84,000 L | 90,000 L | 96,000 L |
12m × 6m | 100,800 L | 108,000 L | 115,200 L |
Older NZ pools — particularly the Cascade-profile pools built through the 1970s and 80s — often have a long flat shallow section before the floor drops away. Those pools read high on the standard calculation. The depth step below explains how to correct for it.
Step one — length and width
Measure at the normal operating water level, from the inside faces of the walls. Not across the coping, not across the paving.
For a rectangular pool: the longest side, and the widest point across it, taken at right angles.
For a curved or freeform pool: run a rope around the outermost points to form the smallest rectangle that contains the whole pool, then measure that rectangle. The shape factors in step three correct for the space your pool doesn't occupy.
Work in metres, to the nearest centimetre.
Step two — average depth
Measure at the shallowest point and the deepest point, add them, divide by two.
(Shallow depth + Deep depth) ÷ 2 = Average depth
A pool 1.1m at one end and 1.9m at the other has an average depth of 1.5m.
The correction most people miss. That method assumes an even slope from end to end. If your pool has a long flat shallow section and then drops sharply — a hopper or Cascade-style floor — the real average is lower, and your volume will read high by 10% or more.
Take depth readings at four evenly spaced points along the length and average those four instead. On a pool that's 1.2m for the first six metres and then drops to 2.0m, that difference is thousands of litres and it will show up in every chemical dose you make for the next decade.
Step three — the formula
Volume in cubic metres × 1,000 = volume in litres. A cubic metre of water is exactly 1,000 litres.
Pool shape | Volume in litres |
Rectangular or square | Length × Width × Average depth × 1,000 |
Circular | 3.14 × Radius × Radius × Average depth × 1,000 |
Oval | Length × Width × 0.785 × Average depth × 1,000 |
Kidney or freeform | Length × Width × 0.75 × Average depth × 1,000 |
The 0.785 and 0.75 factors account for the corners a rectangle has and your pool doesn't. Skip them on an oval pool and you'll overstate by roughly a fifth — and overdose it by the same margin, every time, indefinitely.
Worked example
A rectangular pool: 10m long, 5m wide, 1.2m at the shallow end, 1.8m at the deep end.
Average depth: (1.2 + 1.8) ÷ 2 = 1.5m
Volume: 10 × 5 × 1.5 = 75 cubic metres
In litres: 75 × 1,000 = 75,000 litres
A circular pool 5m across, average depth 1.3m: radius is 2.5m, so 3.14 × 2.5 × 2.5 × 1.3 = 25.5 cubic metres, or 25,500 litres.
An attached spa
If the spa shares water with the pool, calculate it separately and add the two figures together. A residential spa typically holds 1,000–2,000 litres — small next to a pool, but enough to shift a dose.
If it's plumbed independently on its own water, keep the two figures apart and treat them separately.
What the number is for
Chemical dosing
Every dose rate on every label is stated per volume of water. Once the litres are fixed, the arithmetic is fixed.
Worked against a 75,000 litre pool:
To achieve | Rate | 75,000 L pool |
Raise free chlorine 1 ppm — liquid, 12.5% | 80 mL / 10,000 L | 600 mL |
Raise free chlorine 1 ppm — granular cal hypo, 65% | 15 g / 10,000 L | 115 g |
Raise stabiliser (cyanuric acid) 10 ppm | 100 g / 10,000 L | 750 g |
Salt pool — reach 4,000 ppm from fresh water | 4 kg / 10,000 L | 300 kg |
Test before dosing and follow the label on the product in your hand — concentrations differ between brands, and the figures above are the common formulations. Add chemicals to water, never water to chemicals, and never combine products.
New Zealand's UV load is high by international standards. Stabiliser levels that would be adequate in the northern hemisphere leave chlorine burning off through a Kiwi summer, which is why the stabiliser row above matters more here than the guidance printed on imported packaging suggests.
Pump and filter sizing
A pool should turn over its full volume in six to eight hours of filtration.
Volume ÷ 8 = minimum flow rate in litres per hour
The 75,000 litre pool needs to move at least 9,400 L/h. That number sizes the pump — not the pool's dimensions, and not whatever the previous owner installed. Undersized, the water never fully clears no matter how long it runs. Oversized, water is pushed through the filter faster than the media can clean it, and you pay more in power for the privilege.
Heating
Volume determines how much water a heater has to lift. It's the starting figure for sizing, and it's why two pools with identical surface areas can need different units.
Heating requirements also vary sharply by region. A pool in Whangārei or Auckland heats faster and holds temperature longer than the same pool in Christchurch, Queenstown or Central Otago, where the season is shorter and the overnight losses are steeper. Take your volume figure to the sizing conversation rather than working from a headline kilowatt rating.
Refilling — after a liner replacement or a full drain
When a liner is replaced the pool is emptied and refilled. Your volume figure is the refill.
Volume in litres ÷ 1,000 = cubic metres of water
The 75,000 litre pool is 75 cubic metres. Multiply by your council's volumetric water charge for a mains cost, or divide by roughly 10,000 for the number of tanker loads if you're trucking it in.
A few things worth knowing before you book the work:
Filling from mains on a standard household connection generally takes most of a day for a pool this size.
Water charging varies by district. Auckland, Tauranga and Wellington are metered and volumetric. Much of Canterbury and parts of Otago are on rates-funded or unmetered supply, where the cost is negligible but the flow rate may be the constraint.
Summer restrictions apply across much of the country and can prohibit filling a pool from mains outright. If a liner replacement is planned for December through February, confirm your district's position before scheduling.
Rural and tank supply. If you're not on town supply, a full refill is a tanker job. At roughly 10,000 litres per load, the 75,000 litre pool is seven to eight deliveries, and that needs booking ahead in peak season.
A liner replacement leaves the shell, plumbing and surrounds untouched. Only the surface is renewed. It's the reason a vinyl liner pool can be returned to a new-condition finish decades into its life, in a way a concrete or fibreglass shell cannot.
Sanity-checking your answer
Water meter method. Read the meter, top the pool up by a measured amount, read it again. Not a full verification, but it will expose a badly wrong calculation immediately.
The benchmark. Most residential inground pools in New Zealand fall between 25,000 and 80,000 litres. Land well outside that and the average depth is almost always the culprit — check the flat-shallow-section correction above first.
What volume does not tell you
A replacement liner is not calculated from a volume figure. It's made to the measured shape of the pool — wall heights, floor profile, hopper slope, steps, benches and fitting positions. Those measurements are taken on site, and every Aqua-Tech liner is cut to them.
Volume tells you how much water the pool holds. It says nothing about the shape the liner has to take.
Frequently asked questions
Do I measure depth from the waterline or the top of the pool? From the normal operating water level down to the floor. The freeboard above the waterline holds no water.
My pool has a long flat shallow end. Does this still work? Not accurately. Averaging only the shallowest and deepest points will overstate your volume. Take readings at four evenly spaced points along the length and average those.
How accurate does the figure need to be? Within about 5% is fine for dosing and equipment sizing. It doesn't need to be exact — it needs to be close enough that you're not treating a pool half again the size of the one you own.
How much water does it take to refill my pool? The same as its volume. Divide litres by 1,000 for cubic metres, then apply your council's water charge — or divide by roughly 10,000 for the number of tanker loads.
Can I fill a pool during a summer water restriction? It depends on your district and the restriction level. Several councils prohibit filling from mains under moderate restrictions. Check locally before scheduling a drain-and-refill over summer.
Does an attached spa count? If it shares water with the pool, yes — work it out separately and add it in. If it's plumbed independently, keep the figures separate.
Is my volume used to size a replacement liner? No. A liner is made to the measured shape of the pool — wall height, floor profile, steps and fittings — not to a volume figure.
Manufactured in New Zealand since 1974
Aqua-Tech has manufactured pool liners from our Onehunga factory for over fifty years, supplying pools throughout New Zealand. If you need help confirming your volume, matching chemicals or equipment to it, or you're weighing up a liner replacement, we're glad to talk it through.
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