Volume, pressure, flow rate, household sizing, treatment dosing, rainwater harvesting, irrigation, structural load, cost — all in one place. Free. No sign-up. Works on any device.
Used daily by homeowners, farmers, engineers & emergency planners
Whether you're sizing a rooftop tank for your home, calculating irrigation requirements for a farm, figuring out if your roof can handle the load, or prepping emergency water storage — you're in the right place.
Every calculator here is free, gives instant results, supports both metric and imperial units, and works on any device. No accounts. No paywalls. No nonsense.
From a simple volume check to full irrigation system planning — every water tank scenario covered.
The tools people reach for most often — start here if you're not sure where to begin.
Start with your situation — find the exact tool that answers it.
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. We cite the source standard for each formula, explain what the inputs mean and why they matter, and flag anywhere an estimate requires professional verification.
We cover household users in Karachi sizing a rooftop tank, farmers in Australia calculating drip irrigation storage, preppers in the US planning emergency stockpiles, and engineers double-checking quick numbers on a job site. One resource. Every scenario.
Read our full methodology and about page →Four steps. No account. No waiting.
Whether you're a homeowner, farmer, or prepper — there's a set of tools built for you.
No black boxes. Every calculator's core equation is documented, sourced, and explained.
These are three examples. Every calculator page shows its full equation, variable definitions, and the standard it references. Read our guides for deeper methodology explanations.
Built for accuracy. Designed for real use. No filler.
The questions we get asked most often — answered clearly.
65+ free online calculators across 10 categories: volume & capacity (11 tools), household sizing (6), refill & flow (6), weight & structural load (5), pressure & height (6), water treatment (10), rainwater harvesting (7), agricultural & irrigation (9), cost & comparison (8), and emergency & survival (6).
For a rectangular tank: Volume (litres) = Length × Width × Height (in cm) ÷ 1,000. For a cylinder: Volume = π × radius² × height ÷ 1,000. Our calculators handle the math and unit conversions automatically — just enter your dimensions.
A general rule: 150–200 litres per person per day. A 4-person household needs 600–800 litres for one day of backup, or 1,200–1,600 litres for two days. In areas with unreliable supply, 3–5 days is recommended. Use our Water Tank Size for Home Calculator for a precise recommendation.
Yes, completely free. No account, no registration, no subscription. Every single calculator on the site is available to everyone without any restriction.
Yes. Every calculator is fully responsive and optimised for touch input. They work on all modern smartphones, tablets, and desktop browsers with no app installation required.
A US gallon equals 3.785 litres. A UK (Imperial) gallon equals 4.546 litres — about 20% larger. Our calculators always display both side by side so there's no confusion. Use the Litres to Gallons Converter to switch between them.