Water Tank Volume Calculator
A free, browser-based calculator. Runs entirely in your browser — no sign up, nothing stored.
Enter Values
How to use this calculator
- Enter the tank's diameter and height.
- Optionally enter the current water depth to see how much is in it now.
- Read the capacity in litres, cubic metres and US gallons.
How it works
A round tank is a cylinder: volume = π × (diameter ÷ 2)² × height. Multiplying cubic metres by 1,000 gives litres.
If you enter the current water depth, the same formula with that depth gives how much water is in the tank and the percentage full.
Worked example
3 m diameter, 2 m high. π × 1.5² × 2 = 14.14 m³ ≈ 14,137 litres (about 3,734 US gallons).
Common mistakes
- Entering the radius in the diameter field — measure the full width across the tank, not from the centre.
- Mixing units, e.g. diameter in metres and height in millimetres — keep both the same.
- Treating the figure as usable volume — the outlet sits above the floor, so a little can't be drawn off.
Frequently asked questions
How do I find the capacity of a rectangular tank?
For a square or rectangular tank, use length × width × height instead, then × 1,000 for litres — the water tank formula here is for round (cylindrical) tanks.
How many litres are in a cubic metre?
1,000 litres. So a 14.14 m³ tank holds about 14,137 litres.
Is the capacity the same as usable water?
No — it's the geometric capacity. Real usable volume is a little less because the outlet is above the base and fittings take up some space.
Related tools
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.