About the Tank Volume Calculator
Water butts, fish tanks, fuel tanks and drums all hold a certain volume, and it is not always on the label. This calculator works out the volume of a rectangular tank from its length, width and height, or of an upright round tank from its diameter and height. A fill level lets you find how much liquid is in a partly full tank. Sizes are in centimetres and the answer is in litres, US gallons, UK gallons and cubic metres. Type the shape, the dimensions in centimetres and the fill level and the tank volume appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Tank Volume Calculator
- 1Enter the shape, the dimensions in centimetres and the fill level.
- 2Pick the units or options from the menus if the tank volume tool offers them.
- 3Read the tank volume in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the tank volume
People use it for aquariums, rainwater tanks, heating-oil tanks, ponds and drums. Knowing the volume lets you work out how much water to treat, how much fuel to order, or how long a tank will last at a given rate of use.
Use inside dimensions, not outside, because the walls take up room. A tank on its side needs a different formula, as the liquid depth is not proportional to the volume. This tool covers upright tanks only.
How the tank volume is worked out
Rectangular: volume = length × width × height. Round: volume = π × (diameter ÷ 2)² × height. One litre is 1,000 cubic centimetres. A rectangular tank 100 cm long, 50 cm wide and 60 cm high holds 300 litres, which is 79.3 US gallons or 66 UK gallons. An upright round tank 100 cm across and 100 cm tall holds 785.4 litres. At 50 percent full the first tank holds 150 litres.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Two shapes
- Fill level
- Four volume units
Mistakes to avoid with tank volume
The fill level is for the height of the liquid as a share of the height of the tank. A percentage of height equals the same percentage of volume only in tanks with straight vertical sides. Fish tanks are never filled to the brim, so allow for that with the fill level.
On phone and computer
On a phone, type into the boxes one after another and read the tank volume underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the tank volume move. The tank volume calculator works the same on both. A tank is one shape among many, so other volume tools help. Use the Volume Calculator for boxes and cones, the Pool Volume Calculator for pools, and the Aquarium Volume Calculator for fish tanks.
Features
- Measure inside dimensions
- Upright tanks only
- Leave room at the top
- Clear messages when the tank volume inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate tank volume?
Rectangular: volume = length × width × height. Round: volume = π × (diameter ÷ 2)² × height. One litre is 1,000 cubic centimetres. A rectangular tank 100 cm long, 50 cm wide and 60 cm high holds 300 litres, which is 79.3 US gallons or 66 UK gallons. An upright round tank 100 cm across and 100 cm tall holds 785.4 litres. At 50 percent full the first tank holds 150 litres.
What is the formula for tank volume?
Rectangular: volume = length × width × height. Round: volume = π × (diameter ÷ 2)² × height. One litre is 1,000 cubic centimetres. The tank volume calculator applies it exactly and rounds only the displayed answer to six significant figures.
How many litres in a cubic metre?
1,000.
How do I measure a round tank?
Measure the inside diameter and the inside height.
What about a horizontal cylinder?
The partial volume depends on the liquid depth in a curved way. This tool does not cover it.
Is this tank volume calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.