# Water Tank Capacity Calculator > Free water tank calculator: litres, gallons, m³ and ft³ for a rectangular, vertical or horizontal tank — plus weight of water, fill level and fill time, or size a tank for your household. Metric or imperial, in your browser. Litres, gallons, m³ and ft³ for a tank of any shape — plus weight of water, fill level and fill time, or size a tank for your household. Metric or imperial, all in your browser. - **HTML page:** https://siteometry.com/en/tools/water-tank-capacity-calculator - **Category:** [Area & Conversions](https://siteometry.com/en/tools/category/area-conversions) - **Figures live on the page:** tables, diagrams and worked figures the text refers to ("the table below") are drawn by the page and are not reproduced here. Each section below links to its anchor on the page. - **Runs in the browser:** Siteometry calculators need no account and send no input anywhere — every number below is computed on the visitor's own device. ## How to calculate water tank capacity 1. **Choose your units** — Switch between metric (litres, m³) and imperial (US gallons, ft³). 2. **Pick a mode** — Use tank capacity to size a known tank, or sizing to pick a tank for a household. 3. **Pick the tank shape** — Choose rectangular, vertical cylinder or horizontal cylinder. 4. **Enter the dimensions** — Type the tank's dimensions, and an optional water depth for a part-full reading. 5. **Read the results** — Read the capacity, unit conversions, weight of water and fill time. _On the page: https://siteometry.com/en/tools/water-tank-capacity-calculator#howto_ ## Water tank capacity calculator Work out how much water a tank holds in litres, US gallons, cubic metres or cubic feet — for a rectangular tank, an upright cylinder or a cylinder lying on its side. Enter a water depth to read the litres in a part-full tank and how full it is, see the weight of the water for structural load, or switch to sizing mode to pick a standard tank for your household. Everything runs in your browser. _On the page: https://siteometry.com/en/tools/water-tank-capacity-calculator#watertank-guide-intro_ ## How the calculator works Pick your units and mode, choose a tank shape and type its dimensions. The capacity, unit conversions and — where you supply them — the fill level, weight and fill time update as you type. _On the page: https://siteometry.com/en/tools/water-tank-capacity-calculator#how-calculator-works_ ## Tank volume formulas A rectangular tank holds length × width × height. An upright (vertical) cylinder holds π × r² × height, and a cylinder lying on its side holds π × r² × length, where r is half the diameter. One cubic metre is 1,000 litres, and one litre of water weighs one kilogram. _On the page: https://siteometry.com/en/tools/water-tank-capacity-calculator#tank-shape-formulas_ ## Litres in a part-full tank For a rectangular or upright tank the water volume rises in step with the depth. A cylinder lying on its side is different: the water surface is a chord across the circular end, so the volume follows the circular-segment area of the filled part of the end. Enter a water depth and the calculator returns the current litres and how full the tank is. _On the page: https://siteometry.com/en/tools/water-tank-capacity-calculator#partial-fill_ ## Sizing a tank Sizing mode multiplies the number of people by a typical daily use per person and the days of storage you want to keep, then recommends the smallest standard off-the-shelf tank that covers it. The demand and tank-size figures are typical, editable assumptions — confirm the right size for your supply and local availability. _On the page: https://siteometry.com/en/tools/water-tank-capacity-calculator#sizing-a-tank_ ## Frequently asked questions ### How do I calculate the capacity of a water tank? Find the volume from the tank's shape — length × width × height for a box, or π × r² × height/length for a cylinder — then multiply cubic metres by 1,000 to get litres. This calculator does it for you and also shows US gallons and cubic feet. ### How many litres are in my tank right now? Enter the tank's dimensions and the current water depth. For a rectangular or upright tank the volume is proportional to the depth; for a cylinder on its side the calculator uses the circular-segment area so the part-full figure is exact. ### What size water tank do I need for my family? Switch to sizing mode and enter the number of people, a typical daily use per person and how many days of storage you want. The calculator recommends the smallest standard tank that covers it. The figures are typical assumptions you can edit. ### How do I convert between gallons and litres? One US gallon is about 3.785 litres. The calculator always shows the capacity in litres, US gallons, cubic metres and cubic feet at once, so you can read whichever unit you need. ### How much does the water in a tank weigh? Water weighs about one kilogram per litre (1,000 kg per cubic metre, or about 8.34 lb per US gallon). The calculator shows the weight of a full tank and of the current fill, in tonnes or short tons. ### How long does it take to fill a tank? Enter a flow rate and the calculator divides the volume to fill by that rate to estimate the fill time in minutes. ### Does it work in metric and imperial? Yes. Toggle the units and every dimension and result converts between metric (litres, m³, metres) and imperial (US gallons, ft³, feet). ### Is the calculator private? Yes. Everything is calculated in your browser — your inputs are never uploaded, and your last project is saved only on your device. _On the page: https://siteometry.com/en/tools/water-tank-capacity-calculator#faq_ ## Related calculators - [Pool Volume Calculator](https://siteometry.com/en/tools/pool-volume-calculator) - [Land Area Unit Converter — Bigha, Katha, Gunta & Acre](https://siteometry.com/en/tools/land-area-unit-converter) - [Square Footage Calculator — Area of Any Room or Shape](https://siteometry.com/en/tools/square-footage-calculator) - [Board Foot Calculator — Lumber, Volume & Cost](https://siteometry.com/en/tools/board-foot-calculator)