Pool Volume Calculator
Gallons and litres for rectangular or round pools.
Lumber & Materials
Tank Volume Calculator
Capacity and current fill volume for cylindrical, rectangular and oval tanks, in gallons and litres.
Your result
Sample values940
Gallons total
125.7
Cubic feet
3,558
Litres total
752
Gallons at current fill
Horizontal cylinder, 4 ft by 10 ft, filled to 30 in.
Fill reference
| Depth | Volume |
|---|---|
| 12 in | 246 gal |
| 24 in | 564 gal |
| 30 in | 752 gal |
| 36 in | 875 gal |
| 48 in — full | 940 gal |
How to use this calculator
Pick the shape first, because it changes which dimensions you are asked for. A horizontal cylinder needs diameter and length; a vertical one needs diameter and height; a rectangular tank needs all three.
For current contents, measure the liquid depth from the bottom of the tank with a dipstick. Partial volume in a horizontal cylinder is not proportional to depth — a tank half full by depth is exactly half full by volume, but a quarter of the depth holds far less than a quarter of the volume.
Formula
Cylinder = π × Radius² × Length
Rectangular = Length × Width × Height
Gallons = Cubic feet × 7.481
- π
- approximately 3.1416
- 7.481
- US gallons in a cubic foot
Partial fill in a horizontal cylinder uses the circular segment area, not a simple ratio of depth.
Worked example
A horizontal cylindrical tank, 4 ft diameter and 10 ft long, with 30 in of liquid.
- Radius: 4 ft ÷ 2 = 2 ft
- π × 2² = 12.57 ft² of cross section
- 12.57 ft² × 10 ft = 125.7 ft³ total
- 125.7 ft³ × 7.481 = 940 gallons full
- 30 in of 48 in is 62.5% of the depth
- Circular segment at that depth = 80% of the area, so 752 gallons
940 gallons full, 752 gallons at 30 in
Understanding your results
The relationship between depth and volume is the part most people get wrong on a horizontal tank. The cross section is a circle, so the first few inches at the bottom hold very little, the middle band holds a great deal, and the last few inches at the top hold little again. That is why the fill reference table above is not evenly spaced.
Internal versus external dimensions matter on thick-walled tanks. A quarter inch wall on a small tank is a rounding error; on a poly tank with a one inch wall it is worth deducting, since capacity depends on the square of the internal radius.
Questions
About this calculator
On a horizontal cylinder it is — that is the one depth where the geometry is symmetrical. At any other level it is not, because the width of the liquid surface changes as the level rises. This catches people out when checking heating oil with a dipstick.
Inside if you can reach, since capacity is an internal volume. If you can only measure externally, enter the wall thickness so it can be deducted. On a large steel tank the difference is negligible; on a small thick poly tank it is several percent.
A US gallon is 3.785 litres and an imperial gallon is 4.546, so an imperial gallon is about twenty percent larger. The results here are US gallons. Check which one your supplier quotes before comparing a tank capacity against a delivery.
For the geometry, yes — a tank is a tank. But do not fill any tank to its geometric capacity. Liquids expand, and most tanks are designed with an air gap and a fill limit, commonly around ninety-five percent, that the manufacturer specifies.
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Estimates, not specifications.
Results are based on the values you enter and on typical material
properties. Densities, coverage rates and product sizes vary between
suppliers, so confirm quantities against your supplier's data before
ordering. Structural work must be signed off by a qualified
professional and meet your local building code.