Who We Are
The engineer behind the numbers
Every calculator and guide on this site is written and reviewed by one named, accountable engineer. When a number on this site is wrong, there is a person responsible for fixing it.
We built the resource we always wished existed — a single place where anyone, anywhere, can run a precise water tank calculation in seconds, without signing up, without paying, and without getting an answer that's wrong.
Whether you're a homeowner trying to figure out if your rooftop tank can last the weekend, a farmer sizing a storage reservoir, or an emergency planner stockpiling supplies — you deserve a fast, accurate, jargon-free answer.
Water scarcity affects billions of people. In many parts of the world, getting a tank sizing wrong doesn't mean an inconvenience — it means running dry. Yet professional calculation tools were either locked behind expensive software licenses, buried in spreadsheets shared on engineering forums, or simply didn't exist for the full range of use cases people actually face.
We started by solving our own problem: a simple, single-page tool to calculate rectangular tank volume. Then users kept asking for more — cylindrical tanks, rooftop weight loads, chlorine dosing, rainwater catchment, drip irrigation sizing. We built each one from published formulas and guidance, with real unit conversion and a mobile-first design.
Today WaterTankCalculator.com covers 75 calculators across 10 categories, used by homeowners, engineers, farmers, aid workers and students. All of it is free to use, with no sign-up.
Every calculator and guide on this site is written and reviewed by one named, accountable engineer. When a number on this site is wrong, there is a person responsible for fixing it.
People use these tools to size tanks, dose drinking water and check roof loads. These are the commitments we actually keep — no more, no less.
Calculators are reviewed by John Mac, PE. Each reviewed page shows his name and the date of the last review, so you know who checked it and when.
When a page says "EPA recommends" or "CDC advises", that figure is checked against the agency's own publication and linked in the page's Sources section. If we can't trace a claim, we remove it.
Formulas are worked through with known values and compared with the tool's output. Reference tables are recalculated from the same formula so the table and the calculator agree.
When guidance changes or a reader reports a problem, the page is reviewed again, fixed if needed, and re-dated. Report an issue on our contact page.
Tools that affect drinking water or structural loads say clearly when water isn't safe to drink yet, or when a licensed engineer needs to check the design. We don't overstate what a calculator can tell you.
Calculations run in your browser, and the numbers you enter aren't sent to our servers. The site is supported by Google AdSense, which uses cookies — see our Privacy Policy.
Calculators accept US and metric units — even mixed in one calculation — and show gallons, feet, psi and pounds alongside litres, metres, bar and kilograms. US and UK gallons are kept separate, because mixing them up is one of the most common sizing errors.
Most people check a tank on site, not at a desk. Every tool is designed to work on a phone first. If something is hard to use, tell us and we'll fix it.
This is the process John follows when a calculator is built or reviewed.
We start from the governing source for the calculation — a government or international agency (US EPA, CDC, WHO, FAO), a code or standards body (the International Plumbing Code, ASCE 7, AWWA) or an established hydraulics text. Because our readers are worldwide, we add the matching UK, European, Australian or Indian source where it differs. Where credible sources disagree, we say so on the page.
We write out the full formula with dimensional analysis. Unit conversion chains are verified independently — a litres-to-gallons conversion is not a rounded multiplier; it uses the exact legal definitions (1 US gallon = 231 cubic inches = 3.785411784 L; 1 imperial gallon = 4.54609 L).
We run the tool against known values — worked examples from the source, hand calculations and manufacturer data where available — and check that any reference table on the page matches the calculator. Every calculator page carries its own worked example, in US units, so you can repeat the check yourself.
Zero values, extreme dimensions, unit boundary crossings, and mixed-unit inputs are all tested explicitly. A calculator that returns "NaN" or a negative volume for any valid input combination is not ready to publish.
Technical accuracy is only half the job. Labels, units and result explanations are written for non-specialists, and safety notes are added wherever a result affects drinking water or structural loads.
After launch, reader reports are treated like bug reports: we trace the problem back to the formula or the source, fix it if needed, and update the review date on the page.
We don't invent formulas or figures. These are the main sources our calculators and guides are checked against — from the US first, and from the UK, Europe, Australia, India and international bodies where they apply.
Our tools are used by people making decisions that matter — from a family checking their tank will last the weekend to an NGO sizing emergency storage for a disaster response.
Free water tank calculation tools for every stage of a project — from basic geometry and sizing to pressure, treatment, rainwater, irrigation, cost and emergency planning.
The calculators and guides are written and reviewed by John Mac, PE, a Texas-licensed Professional Engineer with more than 13 years in residential and light-commercial water storage. A small in-house team handles development, design and publishing. Reviewed pages show John’s name and the date of the last review.
Our calculators use standard formulas and published guidance, and reviewed tools are checked against hand calculations and known values. For most applications — household sizing, volume estimation, flow rate, weight, pressure — results are accurate to within the precision of your input measurements. For safety-critical or structural applications (such as rooftop load bearing or large-scale pressure systems), we recommend using our results as a preliminary estimate and having a licensed engineer verify the final design.
WaterTankCalculator.com is supported by non-intrusive advertising. We do not sell user data, require sign-ups, put calculators behind paywalls, or lock results behind a subscription. Our founding belief is that access to accurate water planning tools is a public good — especially for users in water-scarce regions who genuinely depend on getting the sizing right. Ads let us keep the lights on without charging anyone.
No. Calculations run in your browser using JavaScript, and the numbers you enter aren’t sent to our servers or stored. Like most free websites, we show ads through Google AdSense, which uses cookies — our Privacy Policy explains what that means and how to control it.
Our calculators are ideal for preliminary sizing, feasibility studies, budget estimates, and educational purposes. For final engineering deliverables — particularly anything involving structural loads, pressure systems, public water supply, or large-scale installations — results should be independently verified and stamped by a licensed professional engineer in your jurisdiction. We note this on every relevant calculator page and do not overstate what our tools are designed for.
Whenever the guidance behind a calculator changes, or a reader reports a problem, the affected page is reviewed and updated. We are also re-reviewing the whole site category by category — checking every formula, worked example, reference table and source — and each reviewed page shows the date of its last review.
We want to know. Use our contact form and choose "Report an error in a calculator". Include the page, the values you entered, the result you got, and the result you expected (with a source if you have one). John reviews every report, and corrected pages show a new review date.
