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Enter your values, then click Calculate result.How this calculator helps
Convert internal tank dimensions into litres without mixing imperial and metric units. This rectangular-tank mode also reports cubic feet and US gallons so capacity can be compared with common supplier specifications.
How to use it
- 1
Measure the internal length, width and usable water depth in feet.
- 2
Calculate capacity and allow space below the overflow instead of filling to the absolute top.
- 3
Compare usable litres with a realistic daily household consumption figure.
Formula and methodology
Volume in cubic feet = length × width × depth. Capacity in litres = cubic feet × 28.3168. Storage days = litres ÷ daily usage.
Uses measured dimensions and editable local rates for preliminary planning. It is not a bill of quantities, structural design or valuation.
Worked calculation example
A tank measuring 6 ft by 4 ft by 4 ft holds about 96 cubic feet, or approximately 2,718 litres before allowing for freeboard and unusable residue.
How to interpret your result
Calculate rectangular water-tank capacity in litres, cubic feet and US gallons from internal dimensions. Read the main result together with the supporting values rather than treating one number as a guarantee. The disclosed method is: Volume in cubic feet = length × width × depth. Capacity in litres = cubic feet × 28.3168. Storage days = litres ÷ daily usage.
Input guide
Measure the internal length, width and usable water depth in feet.
Calculate capacity and allow space below the overflow instead of filling to the absolute top.
Compare usable litres with a realistic daily household consumption figure.
Scenario comparison
| Scenario | What it demonstrates |
|---|---|
| Worked baseline | A tank measuring 6 ft by 4 ft by 4 ft holds about 96 cubic feet, or approximately 2,718 litres before allowing for freeboard and unusable residue. |
| Freeboard check | The water level normally remains below the tank's full internal height. |
| Tank shape stress test | This mode is for rectangular tanks; cylinders require a different volume formula. |
Common mistakes to avoid
- Ignoring freeboard: The water level normally remains below the tank's full internal height.
- Overlooking tank shape: This mode is for rectangular tanks; cylinders require a different volume formula.
- Failing to test usable reserve: Sediment, outlet height and pump protection can leave some water unusable.
Confirm dimensions on site and obtain an itemised quotation or measured bill of quantities from a qualified professional.
What can affect the result?
Freeboard
The water level normally remains below the tank's full internal height.
Tank shape
This mode is for rectangular tanks; cylinders require a different volume formula.
Usable reserve
Sediment, outlet height and pump protection can leave some water unusable.
Limits of this estimate
The result assumes a perfect rectangular interior and does not assess structural strength, leakage, plumbing capacity or water-quality requirements.
Sources and review information
Frequently asked questions
Is the water tank volume calculator free?＋
Yes. SolvePilot tools are free, work in your browser, and require no account.
Does SolvePilot store my values?＋
No. Calculations run locally in your browser and the values you enter are not sent to a server.
Should I treat the result as an exact bill or quotation?＋
No. Results are informed estimates. Final charges can vary because of taxes, tariffs, lender terms, usage patterns, or provider rules.
How can I improve the accuracy?＋
Use recent values from your own bill, statement or institution, review every assumption, and confirm important results with the relevant official source.
Should I use outside or inside dimensions?＋
Use internal dimensions because wall thickness does not hold water.