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Water, Tank & Plumbing Calculators

Rectangular Tank Calculator

Capacity, fill volume and wall area of a rectangular tank or sump in litres and gallons.

Enter values

Results update as you type.

Result

Full capacity

3,600 litres

Usable capacity
3,300 litres
Volume at fill level
3,000 litres
Litres per 100 mm of depth
300
Wall area
8.4 m²
Base area
3 m²
Weight when full
3,600 kg

About the Rectangular Tank Calculator

Capacity, fill volume and wall area of a rectangular tank or sump in litres and gallons.

Also known as: square tank volume, box tank capacity, sump volume calculator, rectangular water tank.

How to use this calculator

  1. Enter length, width, height, fill level and the other fields.
  2. The result updates instantly as you type — press Calculate (or Enter) at any time.
  3. Review the breakdown shown under the main result.
  4. Use Copy result or Share to save the answer or send a link with your inputs.

Formula

V = length × width × height × 1000 litres per m³

Worked example

Using the values pre-filled in the calculator above:

  • Length = 2 m
  • Width = 1.5 m
  • Height = 1.2 m
  • Fill level = 1 m
  • Freeboard to leave = 100 mm

the calculator returns:

  • Full capacity: 3,600 litres
  • Usable capacity: 3,300 litres
  • Volume at fill level: 3,000 litres
  • Litres per 100 mm of depth: 300