Tank Volume Calculator
Calculate cylindrical tank capacity in gallons and cubic feet from diameter and height, plus filled volume at any fill level. For water, fuel, and storage tanks.
How this calculator works
An upright cylindrical tank holds pi × radius² × height of volume. The calculator takes your diameter and height, computes cubic feet, converts to gallons, and scales by your fill level.
Formula: Cubic feet = π × (diameter ÷ 2)² × height. Gallons = cubic feet × 7.48. Filled volume = full × (fill % ÷ 100).
Worked example
A 10-foot diameter, 12-foot tall cylinder, filled 100%:
- Radius: 10 ÷ 2 = 5 ft
- Cubic feet: π × 5² × 12 ≈ 942.5 ft³
- Full capacity: 942.5 × 7.48 ≈ 7,050 gallons
Capacity reference (full, per foot of height)
| Diameter | Gallons per foot of height |
|---|---|
| 6 ft | 211 gal |
| 8 ft | 376 gal |
| 10 ft | 587 gal |
How to measure
Measure the inside diameter across the widest point and the vertical height of the cylinder. Enter a fill level below 100 percent for an upright tank to read the current volume. For a tank on its side, use the full capacity and a calibrated dip chart for partial readings.
Frequently asked questions
How do I calculate a cylinder tank's volume?
Volume equals pi times the radius squared times the height, giving cubic feet, then multiply by 7.48 to get gallons. The calculator does this from the diameter and height you enter — no need to halve the diameter yourself.
Does the fill level work for horizontal tanks?
The fill percentage is linear, which is exact for an upright (vertical) cylinder where each foot of height holds the same volume. A cylinder lying on its side fills non-linearly, so for a horizontal tank use the full capacity and read partial levels from a tank chart instead.
What is the difference between gallons and cubic feet here?
Both describe the same volume. Cubic feet is the raw geometric result; gallons is what tanks are usually rated in. One cubic foot holds about 7.48 US gallons, and the calculator shows both.
How accurate is this for a real tank?
It gives the internal geometric capacity. Real tanks lose a little to wall thickness, fittings, and the fact you rarely fill to the absolute brim, so treat the full number as a maximum and plan for slightly less usable volume.
Can I use this for a round stock tank or cistern?
Yes — any upright round container works: cisterns, rain barrels, stock tanks, and round pools. For a round above-ground pool specifically, the Round Pool Calculator uses the same math with pool-friendly inputs.
Estimates only. Verify quantities with your supplier before purchasing.