The pool volume calculator above works out how much water a swimming pool holds, in US gallons or litres, for rectangular, round, oval and kidney shapes, with a sloped floor running from a shallow end to a deep end. It also returns surface area, average water depth, fill time at your hose or supply flow rate, filtration turnover time, and how many tanker loads the fill would take.
Arb Digital publishes this in a free construction and property estimating set. Pool volume is one of those numbers that gets used far more often than it gets measured — every chemical dose, every heater sizing calculation and every filtration turnover figure depends on it, and if the volume is wrong then every one of those downstream numbers is wrong by the same proportion.
What This Pool Volume Calculator Does
It computes surface area from the shape you choose, works out the average water depth from your shallow and deep measurements less the freeboard, multiplies the two, and converts the resulting volume into gallons or litres. It then divides by your fill flow rate to give a fill time, divides by your pump flow rate to give a turnover time, and divides the padded volume by your delivery load size to give the number of whole loads needed.
It handles things a plain volume tool cannot. Our cylinder volume calculator will give you the volume of a perfectly round tank of constant depth, and that is the boundary between the two pages — it has no sloped floor, no kidney or oval geometry, no waterline allowance and no gallon conversion. For the raw arithmetic on other solids, the sphere volume calculator and the volume converter cover the general cases.
How to Use It
- Pick the shape. Rectangular, round, oval or kidney. If your pool is a freeform design that fits none of these, measure the surface area from a plan and use the last option.
- Enter the dimensions. Length and width at the widest points. Kidney pools need a second width, because they are measured at both of their widest points.
- Set the floor profile. A sloped floor takes a shallow depth and a deep depth. A constant-depth pool takes the same figure in both fields, or you can switch the profile selector.
- Enter the freeboard. Measure your depths to the coping, then tell the tool how far below the coping the water actually sits. Six inches is a common figure but it varies by design.
- Add flow rates. The fill rate gives you a filling time; the pump rate gives you the filtration turnover time, which is the number that matters for water quality.
The Formula / How It's Calculated
Surface area comes first. A rectangle is length × width. A round pool is π × (diameter ÷ 2)². An oval is treated as an ellipse: π × (length ÷ 2) × (width ÷ 2). A kidney is approximated as 0.45 × (width A + width B) × length, which is a long-standing approximation used in the pool trade rather than an exact geometric result — it is close for typical kidney outlines and wrong for unusual ones, which is why the measured-area option exists.
Depth is next. For a constant floor slope, average depth = (shallow + deep) ÷ 2, and that average is exact because the volume under a plane is the volume under its mean height. Freeboard is then subtracted from the average, because water sits below the coping. Volume = surface area × average water depth.
Conversion closes it. One cubic foot of water is 7.48052 US gallons; one cubic metre is 1,000 litres. The USGS gives the same relationship from the other direction in its Water Science School page A Million Gallons of Water — How much is it?, which notes that a million gallons is 133,685.64 cubic feet and describes a pool roughly 267 feet long, 50 feet wide and 10 feet deep to hold it. Fill time is volume ÷ flow rate; turnover time is volume ÷ pump rate.
Why Average Depth Is Not Always the Average of Two Numbers
Averaging the shallow and deep depths is exactly right when the floor is a single flat plane sloping from one end to the other. It is wrong, sometimes badly, when the floor is not.
Most residential pools with a diving area do not have a constant slope. They have a flat shallow shelf, then a transition, then a hopper — a bowl-shaped deep end that occupies only part of the pool's length. Averaging 3 feet and 8 feet gives 5.5 feet, but if the deep hopper occupies only a quarter of the pool's area then the real average depth is much closer to 4 feet. That is a 25 percent error, and it is always in the direction of overstating the volume.
The fix is to split the pool into zones and add them. Measure the shallow shelf as a constant-depth section, the slope as its own section using the average of its two ends, and the deep hopper as a third. Run the calculator once per zone with the surface-area option and add the results. It takes three minutes and removes the largest single source of error in pool volume estimating.
Why the Volume Number Matters More Than It Looks
Almost every decision about pool water is expressed per unit of volume. Chemical dosing instructions are written per 10,000 gallons — the CDC's guidance for home pool and hot tub water treatment and testing describes maintenance dosing in exactly those terms, along with the free chlorine and pH levels that dosing is meant to achieve. If your assumed volume is 20 percent high, every dose you add is 20 percent low relative to the water actually in the pool.
Turnover is the other one. Filtration is usually specified as a turnover time — how long the pump takes to circulate a volume equal to the whole pool — and that figure is volume divided by pump flow. Get the volume wrong and you will either believe your filtration is adequate when it is not, or oversize a pump and pay for the electricity forever. This tool reports turnover alongside fill time for that reason.
Heating scales with volume too, though it scales with surface area for losses. A larger volume takes proportionally longer to bring up to temperature from cold, while ongoing heat loss is dominated by evaporation from the surface — which is why pool covers do far more for running costs than most people expect.
Filling: Time, Flow and What the Supply Can Actually Give
Filling a pool from a domestic supply takes longer than people expect because domestic flow rates are modest. At 10 gallons per minute — a reasonable garden hose figure — a 19,000 gallon pool takes about 32 hours of continuous flow. Two hoses do not necessarily halve that, because both draw on the same service and the pressure drops.
Two practical points. First, check whether your water utility has any restriction or notification requirement for filling a pool; some do, and some offer a sewer credit for water that goes into a pool rather than down the drain, which requires telling them in advance. Second, if you are trucking water in, it arrives in whole loads — the tool rounds up to whole deliveries because half a tanker is not a thing you can buy.
The measurement allowance exists for the same reason. A pool as built rarely matches its drawing to the inch, and the direction of the error is unpredictable. Padding the ordering figure by a few percent costs very little and avoids the specific annoyance of a tanker leaving with the pool four inches short.
Reading the Raw Volume Against the Ordering Volume
Both are on screen. The raw volume is the honest calculation from your measurements, and it is the figure to use for chemical dosing and for turnover, because those need the real quantity of water. The padded ordering volume is the raw figure plus your allowance, rounded up into whole deliveries, and it is the figure to use when buying water.
Do not use the padded figure for dosing. Overstating volume when dosing chlorine or acid means over-dosing, and pool chemistry is a place where more is not better. Use the raw figure there, verify it against a known addition if you can, and keep the padded figure for logistics only.
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Browse Free Tools Talk To Arb DigitalCommon Mistakes to Avoid
- Averaging two depths on a hopper-bottom pool — the deep end occupies only part of the area, so the simple average overstates the volume.
- Measuring depth to the coping — water sits below the coping, and using wall height instead of water depth inflates the volume.
- Applying the padded ordering volume to chemical dosing — dosing needs the real volume, and padding it means over-dosing.
- Forgetting that steps and benches displace water — a large tanning ledge or a set of moulded steps removes a real amount of volume from the total.
- Assuming two hoses fill twice as fast — both draw on the same service, and the combined flow is usually well short of double.
Related Free Tools From Arb Digital
Pair this with the cylinder volume calculator for plain round tanks, the volume converter to move between gallons, litres and cubic metres, the water weight calculator if you need the mass rather than the volume, the concrete calculator for a poured shell and surround and the paver calculator for the deck around it. The free online tools hub lists every calculator we publish.
Frequently Asked Questions
With a floor sloping from 3 feet to 8 feet and the water sitting 6 inches below the coping, the average water depth is 5 feet and the surface area is 512 square feet. That is 2,560 cubic feet, which converts to about 19,150 US gallons at 7.48052 gallons per cubic foot.
The tool uses a trade approximation: 0.45 multiplied by the sum of the two widest widths, multiplied by the length, gives the surface area. It is close for conventional kidney outlines and less reliable for unusual ones, so measure the surface area from a plan and use the measured-area option where accuracy matters.
Usually because the pool has a hopper-shaped deep end rather than a constant slope. Averaging the shallow and deep depths assumes the floor is a single plane. Where the deep section occupies only part of the area, split the pool into zones and add them.
Measure to the coping and then enter the freeboard separately, which is what the form asks for. Using wall height as water depth overstates volume by the freeboard across the whole surface area, which on a large pool is hundreds of gallons.
Divide the volume by the flow rate. At 10 gallons per minute a 19,150 gallon pool takes about 32 hours of continuous flow. Domestic supplies vary widely, and two hoses on the same service do not deliver twice the flow.
Turnover is how long the filtration pump takes to circulate a volume equal to the whole pool, calculated as volume divided by pump flow rate. It depends directly on the volume figure, so an incorrect volume produces an incorrect turnover.
Yes. Moulded steps, tanning ledges and benches all displace water, so a pool with a large ledge holds less than its outline suggests. Estimate the volume of those features and subtract it, or measure the surface area at the waterline for a closer result.
No. It calculates volume only. Water treatment, sanitiser levels and testing are covered by public health guidance and by your local health authority, and dosing instructions come from the product label.
This tool produces volume estimates only. Water treatment, chemical dosing, pool safety and barrier requirements are governed by product instructions, public health guidance and local regulations, and should be confirmed with a qualified professional.
