How to Use the Tank Volume Calculator

Choose the tank shape, select the measurement unit and enter the relevant tank dimensions. The calculator converts those measurements to cubic metres and litres automatically.

You can also enter the percentage of the tank that is currently full to estimate the amount of liquid stored.

The calculator provides:

• Full tank capacity in litres;
• Current liquid volume;
• Remaining tank capacity;
• Volume in cubic metres;
• US gallons;
• UK imperial gallons;
• Fill percentage; and
• Optional liquid value or cost.

How Do You Calculate Tank Volume?

The correct formula depends on the shape of the tank.

Rectangular Tank Volume

If all dimensions are in metres, the result is in cubic metres.

To convert cubic metres to litres:

Rectangular Tank Example

How to Calculate a Cylindrical Tank

For a vertical cylindrical tank:

Because radius is half the diameter:

Cylindrical Tank Example

Suppose a cylindrical tank has:

• Diameter: 2 metres
• Height: 2 metres

Radius:

2 ÷ 2 = 1 metre

Volume:

π × 1² × 2 ≈ 6.283 m³

Capacity:

6.283 × 1,000 ≈ 6,283 litres

Horizontal Cylindrical Tank Volume

A horizontal cylindrical tank has the same full volume as a vertical cylinder of the same diameter and length:

For the fill-percentage setting, this calculator applies the percentage to the full volume as a simplified estimate.

A true horizontal-cylinder liquid-depth calculation is more complex because the relationship between liquid height and volume is not linear.

How Many Litres Are in One Cubic Metre?

Examples:

• 0.5 m³ = 500 litres;
• 1 m³ = 1,000 litres;
• 2.5 m³ = 2,500 litres;
• 10 m³ = 10,000 litres.

How to Convert Litres to US Gallons

Approximately:

How to Convert Litres to UK Gallons

Approximately:

Tank Fill Percentage Calculator

If you know approximately how full the tank is, the calculator estimates:

For example, a 10,000 litre tank at 60% capacity contains approximately:

10,000 × 60% = 6,000 litres

How Much Water Is Left in My Tank?

The remaining capacity is:

A 5,000 litre tank that currently contains 3,000 litres therefore has approximately 2,000 litres of unused capacity.

Can I Use This Calculator for Rainwater Tanks?

Yes. The calculator can estimate the capacity of rectangular and cylindrical rainwater tanks.

Use the internal dimensions where possible because external dimensions can slightly overstate actual usable capacity.

Can I Calculate a Round Water Tank?

Yes. Choose Vertical Cylindrical Tank and enter the tank diameter and height.

Can I Calculate a Horizontal Tank?

Yes. Choose Horizontal Cylindrical Tank and enter its diameter and length.

Can I Use Centimetres or Millimetres?

Yes. The calculator supports:

• Metres;
• Centimetres;
• Millimetres;
• Feet; and
• Inches.

The measurements are converted internally before volume is calculated.

How Many Litres Are in a 1 m × 1 m × 1 m Tank?

A one-metre cube has a volume of one cubic metre.

Therefore:

How Many Litres Are in a 2 m × 1 m × 1 m Tank?

The volume is:

2 × 1 × 1 = 2 m³

Therefore the capacity is approximately:

2,000 litres

Internal vs External Tank Dimensions

For the most accurate capacity estimate, use internal dimensions.

External dimensions include the tank wall thickness and can therefore produce a slightly larger theoretical volume than the actual usable capacity.

Nominal Capacity vs Actual Tank Capacity

Manufacturers may specify a nominal tank capacity that can differ slightly from a simple geometric calculation due to:

• Wall thickness;
• Rounded corners;
• Domed ends;
• Tank fittings;
• Air space;
• Overflow position; and
• Manufacturing tolerances.

The calculator should therefore be treated as an estimate.

How Much Does the Liquid in a Tank Weigh?

For water, one litre weighs approximately one kilogram under ordinary conditions.

This means a tank containing 5,000 litres of water can hold approximately 5,000 kg, or about 5 tonnes, of water alone.

The supporting structure and foundation must therefore be suitable for the tank and its contents.

Tank Volume Calculator Assumptions

This calculator assumes:

• Rectangular tanks have straight sides;
• Vertical cylindrical tanks are true cylinders;
• Horizontal cylindrical tanks are true cylinders;
• Dimensions are measured accurately;
• Dimensions represent usable internal size where possible;
• Fill percentage is applied proportionally to total volume;
• Horizontal partial-fill calculations are simplified;
• One cubic metre equals 1,000 litres;
• US and UK gallon conversions are approximate;
• No allowance is made for fittings or unusable volume; and
• Results are planning estimates only.

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