Work out how many gallons are in a tank: vertical or horizontal, round, rectangular, oval or capsule-shaped, full or partly filled. This tank volume calculator gives you US gallons, liters, cubic feet and the weight of the liquid. This free online tank volume calculator works on any phone or computer, with no sign-up or download.
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Liquid in the tank needed
— US gallons
Quick answer: gallons = volume in cubic feet × 7.48. Vertical round tank: π × r² × h. Rectangular tank: L × W × h. For a horizontal tank, use the partly filled tank shape, which uses the circle-segment formula.
| Tank | Volume (cu ft) |
|---|---|
| Vertical round | π × r² × h |
| Rectangular | L × W × h |
| Oval (elliptical) | π × a × b × h, with a and b the half-widths |
| Capsule (round ends) | π × r² × (4⁄3 × r + a), with a the straight length |
| Horizontal round, filled to depth f | L × [r² × acos((r − f) ÷ r) − (r − f) × √(2rf − f²)] |
Multiply cubic feet by 7.4805 for US gallons (a gallon is 231 cubic inches) or by 28.32 for liters. Use inside dimensions and the height of the liquid, not of the tank.
For a horizontal tank 4 ft across and 10 ft long (940 gallons full):
| Liquid depth | Share of height | Gallons | Share of volume |
|---|---|---|---|
| 1 ft | 25% | 184 | 19.6% |
| 2 ft | 50% | 470 | 50.0% |
| 3 ft | 75% | 756 | 80.4% |
| 4 ft | 100% | 940 | 100% |
Flat or dished end caps add a little. Where the tank maker provides a dipstick chart, use that.
Also: horizontal cylinder, fuel tank, oil tank
V = L × [r² × acos((r − f) ÷ r) − (r − f) × √(2rf − f²)]
r = radius, f = fill depth, L = length.
Example: A horizontal tank 4 ft across and 10 ft long with 3 ft of liquid: 101.1 cu ft = 756 gallons, about 80% of its 940 gallon capacity.
Also: round hole, post hole, tank, planter
V = π × r² × h
r = radius (half the diameter), h = height.
Example: A vertical tank 3 ft across with 6 ft of water: π × 1.5² × 6 = 42.4 cu ft = 317 gallons.
Also: rectangular prism, bed, trench, room
V = L × W × H
L = length, W = width, H = height or depth.
Example: A rectangular tank 4 × 3 ft with 2.5 ft of water: 30 cu ft = 224 gallons.
Also: propane tank, pill
V = π × r² × (4⁄3 × r + a)
r = radius, a = length of the straight middle part.
Example: A capsule tank 2 ft across with a 4 ft straight middle: π × 1² × (4/3 × 1 + 4) = 16.8 cu ft = 125 gallons when full.
Also: elliptical cylinder, stock tank, oval pool
V = π × a × b × h
a = half the long width, b = half the short width, h = height.
Example: An oval stock tank 6 × 3 ft with 2 ft of water: π × 3 × 1.5 × 2 = 28.3 cu ft = 211 gallons.
Find the volume in cubic feet for its shape and multiply by 7.48 for US gallons. A vertical round tank is π × radius² × liquid height; a rectangular tank is length × width × liquid height.
Use the “Partly filled tank” shape. Enter the diameter, the length and the depth of the liquid measured with a dipstick. It uses the area of a circular segment, because the gallons per inch are not the same at the bottom, middle and top of a round tank.
The tank is widest in the middle. A 4 ft tank filled 1 ft deep (25% of its height) holds only about 20% of its volume, but filled 2 ft deep (50%) holds exactly half.
Inside dimensions give the true capacity. If you can only measure outside, subtract twice the wall thickness from the diameter. Tank labels usually state the nominal capacity.
Water weighs about 8.34 lb per US gallon. For fuel, oil or other liquids, choose “Custom” and enter the density in lb per cubic foot from the product’s safety data sheet.
Yes, for the volume. The gallons come from the dimensions you enter; for weight, enter the liquid’s density as a custom material. Follow the tank maker’s chart where one is provided, because end caps and fittings change the real capacity.
Yes. The CalcWall Tank Volume Calculator is completely free and works online in any browser, on a phone, tablet or computer. There is nothing to download and no account to create, and the math runs right in your browser, so results appear as you type.