Tank Volume Calculator

Formula

litres = internal length × width × height in cm ÷ 1,000 × fill fraction

Worked example

With Internal length: 120 cm, Internal width: 60 cm, Internal height: 70 cm, Fill fraction: 80 %, full capacity is 504 L.

Inputs and units

Measure the clear internal length, width, and usable height. The fill percentage is measured against that usable height, not necessarily the tank's outer wall; leave room for freeboard by lowering the measured height or selecting a partial fill.

• Internal length (cm): Measure inside wall to inside wall at the intended fill level.
• Internal width (cm): Exclude wall thickness by taking the usable internal width.
• Internal height (cm): Measure usable liquid height below any freeboard line.
• Fill fraction (%): Enter the share of usable internal height you plan to fill.

Calculation and worked example

Multiplying three centimetre lengths gives cubic centimetres. Divide by 1,000 to obtain litres, because a litre occupies 1,000 cm³. Multiply by the fill percentage divided by 100 for the partial fill; divide those litres by 1,000 for cubic metres In compact notation, litres = internal length × width × height in cm ÷ 1,000 × fill fraction.

A 120 cm by 60 cm by 70 cm interior holds 504,000 cm³, or 504 L when full. At 80% of usable height, the rectangular tank contains 403.2 L, equivalent to 0.4032 m³.

How to use the answer

Full capacity describes the measured rectangular interior. Filled volume is the amount at your chosen level, assuming the tank has straight walls; it can support inventory or water treatment calculations if measurements are reliable.

For an aquarium, measure water height below substrate or decoration only if you want the geometric water space above it. For a storage tank, use actual internal drawings when fittings or thick walls make tape measurements difficult.

Assumptions and checks

This model assumes a level rectangular prism and a fill percentage proportional to height. It does not subtract displacement by pumps, gravel, baffles, rounded corners, or internal supports.

Outer dimensions overstate capacity when walls are thick. Another error is confusing litres with cubic metres: 1 m³ is 1,000 L, while 1 L is only 1,000 cm³.

A 10 cm cube holds 1 L, so a tank of many such cubes should produce a plausible litre count. At 50% fill, the filled volume should be exactly half of the full-capacity result.

Common questions

What does the full capacity result represent?

Full capacity is the rectangular interior at the entered usable height. Filled volume applies the selected percentage to that capacity.

What should I check before relying on this result?

Confirm internal rather than external dimensions, level water height, and displacement by equipment. Use a measured fill for critical dosing.