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Tank capacity calculator
Full or partial capacity for an upright cylindrical tank — read it in gallons or litres and see how much is left to fill.
This tank capacity calculator does more than a plain volume: it shows full capacity, the current liquid volume at the height you enter, and the empty space remaining, so you can see exactly where a tank stands.
How the calculation works
- Measure the tank's inside diameter and halve it for the radius.
- Measure the current liquid height inside the tank.
- The tool computes V = π r² h for the liquid volume.
- Compare it with the full capacity to see how full the tank is.
Worked example. Take a cylinder with a diameter of 20 cm (so a radius of 10 cm) and a height of 40 cm. The base area is π × 10² = 314.16 cm², and multiplying by the height gives a volume of about 12.57 litres (12,566 cm³ · 3.32 US gallons).
| Unit | Equal to |
|---|---|
| 1 US gallon | 231 in³ · 3.785 L |
| 1 Imperial gallon | 277.42 in³ · 4.546 L |
| 1 cubic foot | 7.481 US gal · 28.32 L |
| 1 litre | 0.264 US gal · 0.220 Imp gal |
| 1 US gallon | 128 US fl oz |
The figure is the geometric capacity. Usable capacity is a little lower once you allow for fittings and the headspace you leave at the top, so treat it as a close upper bound.
Every tank capacity page
Each page below targets a specific question and opens with the calculator ready to go: