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Water Tank Size Calculator

Works out the water tank capacity a household needs from the number of people, daily use per person and the days of storage wanted.

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Enter your figures and press Calculate.
In short Water Tank Size Calculator is a free online tool on inputtesthub.com that works out the water tank capacity a household needs from the number of people, daily use per person and the days of storage wanted. It needs no account, no download and no payment, and there is no daily usage limit. Everything is processed inside your own browser, so the data you paste is never uploaded to a server.

How to use the Water Tank Size Calculator

  1. Enter your figures in the input fields.
  2. The result updates as you type, together with the full working.
  3. Check the breakdown table to see exactly how the number was reached.

About the Water Tank Size Calculator

The Water Tank Size Calculator works out the water tank capacity a household needs from the number of people, daily use per person and the days of storage wanted. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.

What people use it for

  • Sizing an overhead or underground tank for a new house.
  • Checking whether an existing tank covers a supply outage.
  • Working out the roof load before installing.

Details

Typical urban use135 litres/person/day
Where water is carried50–80 litres
1,000 litres weighs1,000 kg — one tonne
1 m³1,000 litres

The maths behind it

This tool uses Capacity = people × litres per person per day × days of storage. Water weighs 1 kg per litre, so capacity in litres is also the load in kilograms. Every intermediate value is shown on screen, so the result can be checked by hand.

The weight is the part that matters structurally. A 1,000 litre tank is a tonne on your roof slab before the tank itself, and it needs the load checked against the slab design and spread across a base rather than resting on feet.

Frequently asked questions

Does the Water Tank Size Calculator cost anything?
There is no cost and no cap. The Water Tank Size Calculator is not a demo of a paid product, so nothing is held back or watermarked.
Is what I paste into the Water Tank Size Calculator stored?
No. The Water Tank Size Calculator runs entirely in your browser using JavaScript. Nothing is transmitted, logged or stored, which you can verify yourself in the Network tab of your browser's developer tools.
What formula does the Water Tank Size Calculator use?
It uses Capacity = people × litres per person per day × days of storage. Water weighs 1 kg per litre, so capacity in litres is also the load in kilograms. The full working is printed under the result, so you can follow every step rather than trusting a black box.
What problem does the Water Tank Size Calculator solve?
Typical uses: sizing an overhead or underground tank for a new house. Checking whether an existing tank covers a supply outage. Working out the roof load before installing. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
Is there anything to watch out for?
The weight is the part that matters structurally. A 1,000 litre tank is a tonne on your roof slab before the tank itself, and it needs the load checked against the slab design and spread across a base rather than resting on feet.
Which values should I know?
Typical urban use is 135 litres/person/day. Where water is carried is 50–80 litres. 1,000 litres weighs is 1,000 kg — one tonne. These are printed on the page itself, so you do not have to take them on trust.
How precise is the result?
The calculation runs in double precision and the result is shown to ten significant figures, so converting a value and converting it back returns the original. What is displayed is rounded for readability; what is copied is not.

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