Pool volume calculator
Work out how much water a swimming pool holds in US gallons, imperial gallons, litres, cubic metres or cubic feet — for a rectangular, round, oval or kidney pool, in-ground or above-ground.
Enter your pool's dimensions to read the volume, the weight of the water, how many gallons each inch of depth adds, and how long and how much it costs to fill. There is also a chemical dosing guide to estimate starting doses. Everything runs in your browser — nothing you type leaves your device.
How the calculator works
Every shape is volume = plan-view surface area × average water depth. The calculator works out the surface area from your pool's shape and dimensions, multiplies by the average depth, and converts the result into US gallons, imperial gallons, litres, cubic metres and cubic feet at once.
How to calculate pool volume
- Choose your unitsSwitch between metric (litres, m³, metres) and imperial (US gallons, ft³, feet).
- Pick the pool shapeChoose rectangle, round, oval or kidney to match your pool.
- Choose the depth typeUse a constant depth, or shallow → deep for a sloped-floor pool.
- Enter the dimensionsType the plan dimensions and the depth (or shallow and deep depths).
- Read the resultsRead the volume, unit conversions, water weight, gallons per inch, fill time and cost, and a dosing guide.
A rectangular in-ground pool 16 ft wide × 32 ft long, sloping from a 3 ft shallow end to an 8 ft deep end:
| Measure | Value |
|---|---|
| Shape & size | Rectangle, 16 ft × 32 ft |
| Depth | Shallow 3 ft → deep 8 ft (average 5.5 ft) |
| Volume | 512 ft² × 5.5 ft = 2,816 ft³ |
| US gallons | ≈ 21,065 US gal |
| Imperial gallons | ≈ 17,540 imp gal |
| Litres | ≈ 79,740 L (79.7 m³) |
| Water weight | ≈ 79.7 t (175,800 lb) |
| Gallons per inch | ≈ 319 US gal per inch of depth |
Pool volume formulas
A rectangular pool holds length × width × average depth. A round pool holds π × r² × depth, where r is half the diameter. An oval pool holds (π ÷ 4) × length × width × depth. A kidney pool is estimated as 0.45 × (width A + width B) × length × average depth.
One cubic metre is 1,000 litres, one US gallon is about 3.785 litres, and one imperial gallon is about 4.546 litres. One litre of water weighs one kilogram.
Variable depth and gallons per inch
Most in-ground pools slope from a shallow end to a deep end. For a variable-depth pool the calculator uses the average depth — (shallow + deep) ÷ 2 — which gives the same volume as a flat floor at that average, so the sloped floor and the average level enclose the same amount of water.
Because volume rises in step with depth, each inch (or centimetre) of level always adds the same amount of water: surface area × the slice thickness. That figure is handy when you are topping up the pool or working out a dose from a partial water change.
| Surface area | US gal per inch | Litres per cm |
|---|---|---|
| 200 ft² · 18.6 m² | 125 | 186 |
| 300 ft² · 27.9 m² | 187 | 279 |
| 450 ft² · 41.8 m² | 281 | 418 |
| 600 ft² · 55.7 m² | 374 | 557 |
| 800 ft² · 74.3 m² | 499 | 743 |
Gallons per inch depends only on the water-surface area, not the depth — so it is the same whether your pool is shallow or deep. Find the row nearest your pool's surface area for a quick top-up or dosing figure.
Chemical dosing guide
Once you know the volume, the calculator can estimate typical starting doses for free chlorine, pH, total alkalinity, cyanuric acid (stabiliser), calcium hardness, algaecide and — for saltwater pools — salt. Enter your current and target readings and each dose scales with your pool's gallons.
The figures below are typical, editable reference doses per 10,000 US gallons — not a prescription. Product strengths vary, so always confirm against your own test kit and the product label before adding anything.
| Chemical | Typical product | Ideal range | Typical dose (per 10,000 US gal) |
|---|---|---|---|
| Free chlorine | 12.5% liquid chlorine | 1–3 ppm | ~10.5 fl oz raises FC by ~1 ppm |
| pH up | soda ash | 7.4–7.6 | ~6 oz raises pH by ~0.2 |
| pH down | muriatic acid | 7.4–7.6 | ~8 fl oz lowers pH by ~0.2 |
| Total alkalinity | baking soda | 80–120 ppm | ~1.4 lb raises TA by ~10 ppm |
| Cyanuric acid (CYA) | stabiliser | 30–50 ppm | ~1.25 lb raises CYA by ~10 ppm |
| Calcium hardness | calcium chloride | 200–400 ppm | ~1.25 lb raises CH by ~10 ppm |
| Algaecide | algaecide | weekly maintenance | ~3 oz weekly — label strength varies widely |
| Salt (saltwater pools) | pool salt | ~3,200 ppm | ~83.5 lb raises salt by ~1,000 ppm |
These are typical starting doses per 10,000 US gallons — not a prescription. Product strengths vary widely; always verify with your own test kit and the product label before adding any chemical, and lower a reading only by partial draining and dilution.
Frequently asked questions
How do I calculate the volume of my pool?
Multiply the pool's water-surface area by its average depth. For a rectangle that is length × width × average depth; for a round pool it is π × r² × depth; an oval is (π ÷ 4) × length × width × depth. This calculator does it for you and shows US gallons, imperial gallons, litres, cubic metres and cubic feet at once.
How many gallons are in my pool?
Enter the shape, plan dimensions and depth, and the calculator returns the volume in US gallons and imperial gallons, plus litres, m³ and ft³. As a rough guide, a 16 × 32 ft pool averaging 5.5 ft deep holds about 21,000 US gallons.
My pool has a shallow and a deep end — what depth do I use?
Use the average depth, which is (shallow depth + deep depth) ÷ 2. A pool that slopes from 3 ft to 8 ft averages 5.5 ft. Choose the shallow → deep option and the calculator averages them for you; the sloped floor holds the same volume as a flat floor at the average level.
Is the kidney-pool volume exact?
No — a kidney pool has an irregular curved outline, so its volume is always an approximation. The calculator uses 0.45 × (width A + width B) × length × average depth, which gives a close estimate. It is labelled an estimate throughout the tool.
How much chlorine or other chemicals does my pool need?
Enter your current and target readings in the dosing guide and each dose scales with your pool's volume. As a typical figure, about 10.5 fl oz of 12.5% liquid chlorine raises free chlorine by roughly 1 ppm per 10,000 US gallons. These are typical starting doses only — always confirm with your test kit and the product label.
How much does the water in a pool weigh?
Water weighs about one kilogram per litre (1,000 kg per cubic metre, or about 8.34 lb per US gallon). The calculator shows the total weight in kilograms or pounds, and in tonnes or short tons — useful for delivery or structural checks.
How do I convert between gallons and litres?
One US gallon is about 3.785 litres and one imperial gallon is about 4.546 litres. The calculator always shows the volume in US gallons, imperial gallons, litres, cubic metres and cubic feet at once, so you can read whichever unit you need.
Is the calculator private?
Yes. Everything is calculated in your browser — your inputs are never uploaded, and your last pool is saved only on your own device.