Square Tank Volume Calculator Formula

This calculator works out the volume of a square or rectangular tank in litres, US gallons, and cubic metres. You enter the side length (or width and length) and the height of the tank, and the tool returns the total volume in your chosen units. The formula is simple: Volume = length × width × height, with all dimensions in the same unit.

Formula

The volume of a square tank (a cube or a rectangular prism with a square base) is:

V = a² × h

where:

• V = volume (cubic metres, litres, or gallons)
• a = side length of the square base (metres, feet, etc.)
• h = height of the tank (same unit as side length)

If the tank is rectangular (not square), replace a² with length × width. The formula works for any unit as long as you use the same unit for all three dimensions. To convert cubic metres to litres, multiply by 1000. To convert to US gallons, multiply by 264.172.

Worked Example

Using the default values from the calculator: side = 1 m, height = 1 m.

1. Calculate the base area: 1 m × 1 m = 1 m²
2. Multiply by height: 1 m² × 1 m = 1 m³
3. Convert to litres: 1 m³ × 1000 = 1000 litres
4. Convert to US gallons: 1 m³ × 264.172 = 264.172 gallons

The calculator shows 1.000 m³, 1000.0 litres, and 264.2 US gallons. That matches the manual calculation.

When to Use This Formula

This formula applies to tanks with straight sides and a flat bottom – typical for many aquarium tanks, water storage tanks, fuel tanks, and small swimming pools. It does not apply to cylindrical, spherical, or irregularly shaped tanks. For a cylindrical tank, you would use V = π × r² × h, where r is the radius.

If your tank has a tapered bottom or sloped sides, the simple formula overestimates the volume. In that case, you need the actual dimensions at each depth or a more complex integration.

Common Mistakes and How to Avoid Them

• Mixing units – Always convert all dimensions to the same unit before multiplying. For example, if side is in feet and height is in inches, convert height to feet first.
• Using outside dimensions instead of inside – For a real tank, the wall thickness reduces the internal volume. Use the inside dimensions for accurate capacity.
• Confusing US gallons with imperial gallons – 1 US gallon = 3.785 litres, while 1 imperial gallon = 4.546 litres. The calculator uses US gallons.
• Forgetting to account for water displacement – If you fill the tank with objects (gravel, rocks, decorations), the actual water volume is less than the tank volume. For aquariums, subtract the volume of the substrate and décor.

How to Read the Result

The volume in cubic metres tells you the physical space inside the tank. Litres and gallons are more practical for everyday use – for example, when buying water treatment chemicals or estimating weight. One litre of water weighs approximately 1 kilogram, and one US gallon weighs about 8.34 pounds. So a 1000-litre tank holds roughly 1000 kg of water, which is important for floor loading.

If you are sizing a pump or filter, you usually need the flow rate in litres per hour or gallons per hour, which is the tank volume multiplied by the desired turnover rate (e.g., 4 times per hour for a sump).

Limitations of the Formula

The formula assumes a perfect rectangular prism with flat, parallel sides. Real tanks often have rounded corners, sloped bottoms, or overflow compartments that reduce the usable volume. Also, the formula gives the total volume when filled to the brim – in practice, you usually leave a few centimetres of air space at the top, so the actual water volume is slightly less.

For irregular shapes, consider using a water displacement method: fill the tank with a known volume of water and measure the difference. Or use a flow meter when filling.

Frequently Asked Questions

How do I calculate litres from square tank dimensions in feet?

First, convert all dimensions to feet. Then multiply length × width × height to get cubic feet. Multiply by 28.317 to get litres (since 1 cubic foot = 28.317 litres). For example, a tank 2 ft × 2 ft × 1 ft has 4 cubic feet, which is 113.3 litres.

Does the formula work for a rectangular tank?

Yes, just replace a² with length × width. The calculator above assumes a square base, but the same principle applies. For a rectangular tank, use V = length × width × height.

What is the difference between US gallons and imperial gallons?

US gallons are smaller: 1 US gallon = 3.785 litres. Imperial gallons (used in the UK and some Commonwealth countries) are larger: 1 imperial gallon = 4.546 litres. Always check which gallon your pump or container uses.

How much water does a 2m × 2m × 1.5m tank hold?

Using the formula: 2 × 2 × 1.5 = 6 cubic metres. That equals 6000 litres or about 1585 US gallons. This is a large tank – ensure your floor can support the weight (about 6000 kg).

Why does my tank hold less than the calculated volume?

Possible reasons: wall thickness reduces internal volume, the tank isn’t completely filled, or internal components (baffles, overflow, heater) take up space. For aquariums, substrate and decorations also displace water.

Can I use this formula for a round tank?

No. For a cylindrical tank, use V = π × r² × h, where r is the radius. For a spherical tank, use V = (4/3) × π × r³. This calculator is only for square or rectangular tanks.

Related

• Sphere Tank Volume Calculator: How to Find Capacity
• Pressure Tank Volume Calculator & Sizing Guide
• Rectangular Tank Volume Calculator in Gallons

in side | Side length | m | 1 | 0
in height | Height | m | 1 | 0
out vol_m3 | Volume | m³ | side * side * height | 3
out vol_l | Volume | litres | side * side * height * 1000 | 1
out vol_usgal | Volume | US gallons | side * side * height * 264.172 | 1