Pool calculator
Pool volume calculator: litres, pump size and running cost
Litres for any pool shape, sloped floors included. Then the pump flow and running cost for that volume, old pump against 6 star.
Step 1: How many litres is your pool?
Pick the shape, then enter the inside measurements in metres.
Measure inside the pool, at the water line.
Your pool holds about
44,800 litres
44.8 m³ · 32 m² surface area · 1.4 m average depth
Rectangle: 8 × 4 = 32 m² × 1.4 m average depth = 44.8 m³ × 1,000 = 44,800 litres
Get my price for this poolFills in your pool size on the price form below. NSW homes only.
Step 2: Pump size, as the flow your pool needs
The turnover method: the whole pool through the filter in about 6 to 8 hours.
To turn 44,800 litres over in 6 to 8 hours, the pump needs to move about 93 to 124 litres a minute through the filter. Litres ÷ hours ÷ 60 = litres a minute.
- That is the flow through your filter and pipes, not the nominal flow printed on the box. Pipe runs, bends and the filter take a share of it, so a pump has to be checked at your pool's head: about 15 m for most inground pools and about 9 m for above ground pools, going by one major pump maker's sizing guide.
- Your filter has a maximum flow rate, and the pump should not push past it.
- The installer confirms the pump size from your filter and pipework. A variable speed pump is then programmed to your pool, so it runs slowly for most of the day and speeds up only for cleaning or backwashing.
Step 3: Running cost, old pump against 6 star
Your current single speed pump against a 6 star variable speed pump on the same pool.
From $899 installed ($1,049 in parts of regional NSW), that saving pays the upgrade back in about 15 to 18 months, then keeps saving about $7,070 over 10 years at today's rate.
Your pool is in the medium band (40,000 to 65,000 L), so the 6 star pump is estimated at 600 kWh a year. The hours seed from your pool size; change them to match your timer.
Step 4: Check your NSW rebate price
NSW only.
In NSW, replacing an old pump with a 6 star variable speed pump is from $899 installed after the rebate, against usually $1,400 to $1,600 without it. Your price comes back by text and email within a couple of minutes.
Get my price for this pool $899 applies in Sydney, the Central Coast, Newcastle, the Hunter and the South Coast (Wollongong to Jervis Bay). Elsewhere in NSW it is $1,049. Above ground pools are eligible.Estimates only, based on your measurements, the turnover method, typical single speed pump power draw and energy label figures for 6 star variable speed pumps. Actual volume, flow and running costs vary with your pool, equipment, settings and tariff. Not financial advice.
The installed price and NSW rebate apply to NSW homes.
Get your pool-pump price in 60 seconds
Enter your details and estimated pool size. We’ll instantly text and email your estimated installed price after applicable NSW energy-scheme incentives. From $899 installed in most of NSW.
How do I calculate my pool volume?
Measure the inside of the pool in metres, work out the surface area for its shape, then multiply by the average depth. That gives cubic metres. Multiply by 1,000 for litres.
- Measure the length and width inside the pool, at the water line. Measure from the inside so you get the water, not the coping.
- Measure the depth at the shallow end and the deep end, from the water surface down to the floor.
- Average the depth: add the two and divide by 2. A pool 1.0 m deep at one end and 1.8 m at the other averages 1.4 m.
- Work out the surface area with the formula for your shape (table below).
- Multiply the area by the average depth for cubic metres, then by 1,000 for litres.
Pool volume formulas by shape
D is the average depth in metres. r is the radius, which is half the diameter.
| Shape | Volume in m³ | Notes |
|---|---|---|
| Rectangle or square | Length × width × D | Exact for a flat floor. Use the average depth for an even slope. |
| Round | π × r² × D | π is about 3.1416. A 5 m pool has a radius of 2.5 m. |
| Oval | π × (length ÷ 2) × (width ÷ 2) × D | Treats the pool as an ellipse. If the sides are straight with round ends, the pool holds more: work it out as a rectangle (length minus width, by the width) plus a round pool as wide as the pool. |
| Kidney | 0.45 × (A + B) × length × D | A and B are the widths at the wide and narrow ends. A pool industry approximation. |
| Freeform | Average length × average width × D | An approximation. Take several length and width measurements and average each. |
| L-shape | ((L1 × W1) + (L2 × W2)) × D | Split the pool into two rectangles that do not overlap, then add them. |
| Above ground round | π × r² × water depth | Use the water depth, not the wall height. |
One cubic metre holds 1,000 litres, so the last step is always the same.
How do I calculate the volume of a pool in litres?
Work in metres and the maths stays short. Length × width × average depth gives cubic metres, and each cubic metre is 1,000 litres. A pool 8 m long and 4 m wide with an average depth of 1.4 m is 8 × 4 × 1.4 = 44.8 m³, which is 44,800 litres.
If your pool plans are in feet, convert first: 1 foot is 0.3048 m, so a 26 foot pool is about 7.9 m long. Chemical doses are worked out from the same litres figure, so it is worth writing down.
How to measure a pool, including sloped floors
- Measure inside the walls. Run the tape across the water surface from wall to wall, not across the coping or paving.
- Measure water depth, not wall height. The water sits below the top of the wall, and using the full wall height overstates the volume. This matters most for above ground pools.
- Even slope: if the floor runs in a steady slope from shallow to deep, the average of the two depths is all you need.
- Sudden drop or hopper deep end: if the floor is flat and then drops away, or the deep end is a bowl in the middle, a simple average does not hold. Split the pool into sections (the flat shallow part, the slope, and the deep part), work each one out as its own rectangle, and add them.
- Steps, ledges and swim outs take up a little volume. Leave them in for a pump or running cost estimate. Subtract them if you need an exact figure.
- Attached spa: measure it on its own and add it if it shares the pool's filter.
How to calculate m2 of a pool?
The surface area is the area of the water surface in square metres. For a rectangle it is length × width, so an 8 × 4 m pool is 32 m². For other shapes, use the formula in the table above without the depth. The calculator shows the surface area under the litres for every shape.
If you need the inside area for paint or an interior finish, add the walls. For a rectangle that is roughly 2 × (length + width) × average depth, plus the floor. For 8 × 4 m at 1.4 m average depth: walls 2 × 12 × 1.4 = 33.6 m², floor 32 m², about 66 m² in all.
Worked examples
| Pool | Measurements | Working | Volume |
|---|---|---|---|
| Rectangle, sloped floor | 8 × 4 m, 1.0 to 1.8 m deep | 8 × 4 × 1.4 | 44,800 L |
| Rectangle | 10 × 5 m, 1.5 m deep | 10 × 5 × 1.5 | 75,000 L |
| Round | 5 m across, 1.2 m deep | π × 2.5² × 1.2 | 23,562 L |
| Oval | 8 × 4 m, 1.4 m average | π × 4 × 2 × 1.4 | 35,186 L |
| Kidney | 9 m long, 4.5 m and 3 m wide, 1.4 m average | 0.45 × 7.5 × 9 × 1.4 | 42,525 L |
| L-shape | 8 × 4 m plus 3 × 2 m, 1.3 m average | (32 + 6) × 1.3 | 49,400 L |
| Plunge pool | 4 × 2.5 m, 1.4 m deep | 4 × 2.5 × 1.4 | 14,000 L |
| Above ground round | 4.6 m across, 1.1 m of water | π × 2.3² × 1.1 | 18,281 L |
The 8 × 4 m pool shows why depth matters. At a flat 1.0 m it holds 32,000 litres. At a flat 1.8 m it holds 57,600 litres. With an even slope between the two it holds 44,800 litres. Pool sizes vary widely, so measure your own rather than relying on an average.
What size pool pump do I need?
Pumps are sized on flow, not horsepower. The usual method is turnover: the pump should move the full volume of the pool through the filter in a set time. Pool industry sizing guides work on 6 to 8 hours for a home pool.
That is the flow the pump has to deliver through your filter and pipework. It is not the nominal flow printed on the box. Pipe runs, bends, suction lift and the filter's condition all take a share, and sizing guides put the loss at 20 to 40%. One major Australian pump maker's guide puts most inground pools at about 15 m of total head and above ground pools at about 9 m, so check a pump's flow at that head.
Why bigger is not better
The Australian Government's Energy Rating site advises using the smallest pump suitable for your pool, because pumps that are too large put more pressure on the filter. Your filter also has a maximum flow rate, and running past it can void the filter's warranty. Canstar Blue makes the same point another way: the size of a pool is not always an indication of whether it needs a small or large pump.
Variable speed pumps change the question
A variable speed pump is programmed to the pool. It runs slowly for most of the day to filter, and speeds up only for cleaning or backwashing. Power falls away quickly as speed drops: ActewAGL notes that cutting a pump's speed by 25% can cut its power use by 60%. That is why sizing guides suggest a variable speed pump with a little headroom, set to run slower for longer, rather than a small pump working flat out. Whatever the pool, the installer confirms the size from the filter and pipework on site.
What size pump do I need for a 40,000 litre pool?
Work it through the turnover maths:
- 8 hour turnover: 40,000 ÷ 8 ÷ 60 = about 83 litres a minute (5.0 m³/h)
- 6 hour turnover: 40,000 ÷ 6 ÷ 60 = about 111 litres a minute (6.7 m³/h)
So a 40,000 litre pool needs a pump that delivers roughly 85 to 110 litres a minute through its filter and pipework. Guides that aim for faster or extra turnover get higher numbers: one works a 40,000 litre pool over 4 hours and gets 167 litres a minute, another aims for 1.5 turnovers in 8 hours and gets 125. Any pump that delivers the flow you choose at your pool's head, and within your filter's limit, does the job.
On running cost, a 40,000 litre pool sits in the medium band of the calculator above. An old 1.5 HP single speed pump running 7 hours a day costs about $900 a year at 32c/kWh, against about $190 for a 6 star variable speed pump.
How the running cost estimate works
Step 3 uses the same figures and method as the running cost calculator on the NSW pool pump rebate page, so the two always agree.
- Old single speed pump: power draw × hours a day × 365 × your rate. The calculator uses typical draws of 0.65 kW (0.75 HP), 0.85 kW (1.0 HP), 0.95 kW (1.25 HP), 1.1 kW (1.5 HP) and 1.5 kW (2.0 HP). Canstar Blue gives about 1.1 kW for a 1.5 HP pump.
- 6 star variable speed pump: a yearly energy figure by pool size, based on energy label figures for 6 star models: 450 kWh for pools under 40,000 L, 600 kWh for 40,000 to 65,000 L and 750 kWh above that. The label's yearly figure assumes the pump moves 50,000 litres a day, according to ActewAGL.
- Your rate: the default is 32c/kWh. Change it to the usage rate on your power bill.
Run hours and the time of day change the cost too. See how long to run a pool pump for that, what a pool pump costs in Australia for purchase and install prices, and energy efficient pool pumps for what makes a pump cheap to run.
The NSW Energy Savings Scheme and Peak Demand Reduction Scheme both cover replacing an existing pool pump with a high efficiency model. Through participating scheme pathways it is from $899 installed, against usually $1,400 to $1,600 without the rebate. Above ground pools are eligible, and an existing variable speed pump can be replaced too.
Related pages
FAQ
Pool volume and pump size questions
Multiply the length, width and average depth in metres, then multiply by 1,000. An 8 by 4 m pool with an average depth of 1.4 m holds 44,800 litres. For round, oval, kidney, freeform and L-shaped pools, use the calculator at the top of this page, which applies the formula for each shape.
Measure from the water surface to the floor at the shallow end and the deep end, add the two and divide by 2. A pool 1.0 m deep at one end and 1.8 m at the other averages 1.4 m. That works for an even slope. If the floor drops away suddenly, work out the shallow and deep sections separately and add them.
For rectangles, round pools and pools with an even slope, it is as accurate as your measurements. Kidney, freeform and oval results are approximations, and steps, ledges and bowl shaped deep ends move the true figure a little. That is close enough to size a pump or estimate running costs.
Divide the pool's litres by the pump's flow in litres a minute, then divide by 60 to get hours. Home pools are usually set up to turn over in about 6 to 8 hours. A 44,800 litre pool needs about 93 litres a minute to turn over in 8 hours, or about 124 litres a minute to do it in 6.
No. A pump that is too large puts more pressure on the filter and uses more power than the pool needs. Choose on the flow your pool needs, within your filter's maximum flow rate. A variable speed pump with some headroom is the exception, because it is programmed to run slowly for most of the day.
On the calculator's figures, an old 1.5 HP single speed pump running 7 hours a day costs about $900 a year at 32c/kWh. A 6 star variable speed pump on a medium sized pool costs about $190 a year at the same rate. Step 3 of the calculator works it out for your pump, hours and rate.
In NSW, yes. The Energy Savings Scheme and Peak Demand Reduction Scheme cover replacing an existing pool pump with a high efficiency model, and through participating scheme pathways it is from $899 installed. Above ground pools are eligible. Enter your details in the price form on this page, and your price comes back by text and email within a couple of minutes.
Know your litres? Check your NSW price
Replacing an old single speed pump with a 6 star variable speed pump is from $899 installed after the NSW rebate, against usually $1,400 to $1,600 without it. NSW only.
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