Methodology

How formulas are selected

We use established, published methods: geometry for material quantities; the Hazen-Williams equation for water pipe friction; the standard resistance method (K × I × L ÷ circular mils) for voltage drop; conduction and air-change heat loss for heating loads; the ENERGY STAR room air conditioner chart for room cooling size. Each calculator page lists the formula it uses. If a calculation cannot be done accurately with a simple tool — for example NEC ampacity with all correction factors, or plumbing fixture-unit sizing — we do not fake it; we say what must be checked separately.

How units work

Every input is converted to one internal unit per quantity (feet, square feet, cubic feet, pounds, US gallons per minute, psi, watts, kilowatt-hours, feet per second) using exact definitions — for example 1 ft = 0.3048 m and 1 US gallon = 231 cubic inches. Calculations run at full floating-point precision. Results are converted back to your chosen units and rounded only for display.

How assumptions are handled

Defaults are shown in the input fields, and every assumption that affects the result is listed on the page. Prices are never assumed: you enter your local price. Waste allowances are adjustable because real practice varies by material and layout.

How calculators are tested

Every calculator has automated tests with hand-verified reference values, plus shared tests for zero, negative, very small, very large and invalid inputs, US and metric defaults, unit conversions, and shareable-URL round trips. A calculator cannot display NaN, Infinity or a blank result: invalid inputs produce a plain-language message instead.

When professional verification is required

Structural members and footings, HVAC equipment sizing (ACCA Manual J/S/D), electrical conductor and overcurrent sizing (NEC), plumbing pipe sizing (IPC/UPC), and towing limits (manufacturer ratings) all require verification against the code adopted where you live, the manufacturer’s instructions and your project requirements. Our calculators give preliminary estimates to help you plan, buy materials and ask better questions.