All Water Tank Calculators

How These Calculators Are Built and Reviewed

Each calculator uses the standard formula for its job — tank geometry, hydrostatic pressure (0.433 psi per foot of water), the Hazen-Williams pipe-friction equation, rain depth × roof area, published water-use benchmarks — and shows its working under the result, with a worked example and its sources on the page.

What every tool gives you

• US and metric units side by side — gallons, feet, psi and pounds alongside litres, metres, bar and kilograms. The gallon is the exact US gallon (3.785411784 L); UK gallons (4.54609 L) are shown separately where it matters.
• Sources from several countries — for example NIST and the US EPA, the UK Weights and Measures Act, WHO guidance, US, Australian and Indian building codes for roof loads, and extension services for irrigation figures.
• Honest limits — results are planning estimates. Roof loads, fire-water storage, drinking-water treatment and pressure vessels need a qualified engineer or the local code.

Where to start

• Know the tank's size and need its capacity? Start with Volume & Capacity.
• Choosing a tank for a home or building? Try Tank Size for Home or the Rooftop Tank Size Calculator.
• Putting a tank on a roof or stand? Check the Water Tank Weight Calculator and the Minimum Tank Height for Shower Pressure.

Reviewed by John Mac, PE, Water Systems Specialist

Texas-licensed Professional Engineer with 13+ years in residential water storage and 180+ tank projects. John writes and reviews every calculator on this site.

Last updated October 10, 2026