Tank Volume Calculator
Find the full capacity of a cylindrical or rectangular tank in litres, cubic metres, and gallons.
🛢️ What is the Tank Volume Calculator?
The tank volume calculator works out how much a tank holds from its physical dimensions. Give it the shape and size of a tank and it returns the full capacity in litres, cubic metres, US gallons, and cubic feet at the same time, so you can read the figure in whatever unit your job uses.
It handles the three shapes that cover almost every real tank. A vertical cylinder is the classic upright water or storage tank. A horizontal cylinder is the shape of most fuel and septic tanks lying on their side. A rectangular tank covers box-shaped sumps, cisterns, and aquariums. Farmers sizing a water bowser, plumbers quoting a hot-water cylinder, aquarium owners checking stocking limits, and process engineers costing a chemical vessel all need the same core answer: how many litres or gallons fits inside.
A common point of confusion is diameter versus radius. Tank dimensions are usually quoted as a diameter measured across the full width, but the volume formula needs the radius, which is half of that. This calculator halves the diameter for you, so you enter the number you actually measured. Another frequent mix-up is US versus imperial gallons: a US gallon is 3.785 litres while a UK gallon is 4.546 litres, a difference of about 17 percent that matters when ordering liquid by the gallon.
The tool is useful because it removes both the formula and the unit juggling. You measure, pick your unit, choose the shape, and get an instant capacity in every common unit, along with the step-by-step working so you can check the maths or learn the method.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 - Vertical cylinder water tank
Example 2 - Horizontal cylinder fuel tank
Example 3 - Rectangular cistern
❓ Frequently Asked Questions
🔗 Related Calculators
How do you calculate the volume of a tank?
For a cylindrical tank, Volume = pi x radius squared x height (or length for a horizontal tank). For a rectangular tank, Volume = length x width x height. Compute the volume in cubic metres, then multiply by 1,000 to get litres or by 264.17 to get US gallons. A 2 m diameter, 3 m tall vertical tank holds about 9,425 litres.
How many litres is a cubic metre?
One cubic metre equals exactly 1,000 litres. So a tank with a volume of 7.07 cubic metres holds 7,070 litres. This makes cubic metres a convenient working unit: calculate the volume in cubic metres from the dimensions, then multiply by 1,000 for litres.
How do I calculate the capacity of a cylindrical tank?
Measure the internal diameter and the height (vertical tank) or length (horizontal tank). Halve the diameter to get the radius, then apply Volume = pi x radius squared x height. For a 1.5 m diameter, 4 m long horizontal cylinder the volume is pi x 0.75 squared x 4 = 7.07 cubic metres, or about 7,069 litres.
What is the difference between US and imperial gallons?
A US gallon is 3.785 litres and an imperial (UK) gallon is 4.546 litres, so a US gallon is about 83 percent of an imperial gallon. This calculator reports US gallons. To convert to imperial gallons, multiply the US-gallon figure by 0.8327.
How do I find the volume of a horizontal cylindrical tank?
The full volume of a horizontal cylinder uses the same formula as a vertical one: Volume = pi x radius squared x length. Orientation does not change total capacity. It only matters when the tank is partially filled, which requires a circular-segment area calculation based on the liquid depth.
How many gallons is my tank?
Calculate the volume in cubic metres from the dimensions, then multiply by 264.17 to get US gallons. For example, a rectangular tank measuring 2 m x 1.5 m x 1 m has a volume of 3 cubic metres, which is about 792 US gallons or 3,000 litres.
Does this calculator work for water, fuel, or any liquid?
Yes. Volume depends only on the tank dimensions, not on what it holds, so the litre and gallon figures are the same for water, fuel, oil, or any liquid. If you need the weight of the contents, multiply the volume in litres by the liquid's density (water is about 1 kg per litre).
How accurate is a tank volume estimate?
The geometric formulas are exact for perfectly cylindrical or rectangular tanks. Real tanks may have rounded corners, dished ends, or internal fittings that reduce usable capacity by a few percent. Use the internal dimensions and treat the result as the nominal full capacity.
How do I calculate a partially filled tank?
For a vertical cylinder or rectangular tank, capacity is proportional to fill height, so a tank filled to 60 percent of its height holds 60 percent of its volume. A horizontal cylinder is different: the filled area is a circular segment, so partial volume does not scale linearly with depth.