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Water Tank Sizing For Building Calculator

Work out water tank sizing for building instantly with clear inputs, formula shown and shareable results.

About Water Tank Sizing For Building Calculator

Storage is sized on daily demand, commonly 135 litres per person per day for residential use, multiplied by the days of autonomy required, plus a fire reserve where the code demands one. A cubic metre is a thousand litres, so the conversion to physical tank size is direct.

Formula

Storage

Litres = occupants x litres per person per day x storage days x (1 + fire reserve)

Worked example

With the default values below, Water Tank Sizing For Building Calculator returns Tank capacity required of 9,720. Change any input above and every figure here is recalculated in your browser.

Inputs used

Building occupantsminimum 1
60
Water demand per person per dayminimum 1 L
135 L
Days of storageminimum 0.25 days
1 days
Fire reserve additionaccepts 0–100 %
20 %

Results

Tank capacity required
9,720 L
Daily water demand
8,100 L
Tank volume
9.72 m³
Fire reserve included
1,620 L

Step by step

  1. 1Values used
  2. 2Storage
  3. 3Tank capacity required= 9,720 L
  4. 4Daily water demand= 8,100 L
  5. 5Tank volume= 9.72 m³
  6. 6Fire reserve included= 1,620 L

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Water Tank Sizing For Building figure worked out?

Litres = occupants x litres per person per day x storage days x (1 + fire reserve). Storage is sized on daily demand, commonly 135 litres per person per day for residential use, multiplied by the days of autonomy required, plus a fire reserve where the code demands one.

Should storage be split between underground and overhead?

Usually yes. The underground sump holds the bulk and the overhead tank holds enough for a few hours, which limits the structural load at roof level and the residence time of stored water.

What values do I need to enter?

This calculator takes 4 inputs: Building occupants, Water demand per person per day, Days of storage, Fire reserve addition. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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