Built by People Who Know Water
WaterTankCalculator.com was built out of a straightforward frustration: water tank sizing questions are common, the answers involve real physics and engineering, yet most online resources either get the formulas wrong or bury them behind paywalls and registration walls.
Every calculator on this site is built on documented engineering formulas — the same ones used by civil engineers, plumbers and agricultural consultants — and is written and reviewed by John Mac, PE. Each page shows its working, a worked example in US units and the sources behind it, explains what the inputs mean and why they matter, and flags anywhere an estimate needs professional verification.
We cover preppers in the US planning emergency stockpiles, engineers double-checking quick numbers on a job site, farmers in Australia sizing drip irrigation storage and households in South Asia sizing a rooftop tank — which is why every tool works in US and metric units and draws on US, UK, European, Australian and Indian sources where they differ. One resource. Every scenario.
Read our full methodology and about page →Standards
How every calculator is checked before it goes live
People use these tools to size tanks, dose drinking water and check roof loads, so each one goes through the same review by John Mac, PE:
- The formula is traced to its source — a government agency, a building or plumbing code, or a standard hydraulics text — and the source is listed on the page.
- The tool is run against hand calculations and known values, and every reference table is recalculated so the table and the calculator agree.
- Unit conversions use exact definitions: 1 US gallon = 231 in³ = 3.785411784 L; 1 imperial gallon = 4.54609 L.
- Each page carries a worked example in US units, so you can repeat the check yourself.
- Claims that can't be traced to a source are removed, and pages that touch drinking water or structural loads say clearly when an engineer must check the design.
- Reader reports are treated like bug reports — fixed, re-reviewed and re-dated. Report a problem.