How the calculators work

This page explains how every calculator on this-calculator.com works, so you know what the numbers mean and when to double-check them.

1. One standard formula per page

Each calculator uses the standard formula for its subject, the one found in a textbook or a reference handbook. The page writes it out in words and symbols, defines every variable with its unit, and works an example with the default numbers. Constants (such as π, e, the acceleration due to gravity or a unit factor) are stated where they are used.

2. Inputs and units

• Every input shows its unit next to the box. Enter numbers in that unit; use the unit converter first if yours is different.
• You may type thousands separators (1,250) and decimals with a point (12.5).
• List inputs (for statistics) accept numbers separated by commas, spaces or new lines.
• Drop-down inputs apply a fixed factor, shown in the formula box.

3. How results are calculated and rounded

• Calculations run in full double precision and are rounded only for display. Each result keeps the number of decimals shown in the “Rounding” line beside it.
• Times are shown as minutes and seconds (m:ss) or hours, minutes and seconds (h:mm:ss), rounded to the nearest second.
• Trigonometry uses radians unless the page says degrees.
• Standard deviation and variance are sample values (dividing by n − 1) unless the page says population. Quartiles use the median-of-halves method: Q1 and Q3 are the medians of the lower and upper halves, and when the count is odd the median itself is left out of both halves. Some textbooks and spreadsheet functions use other quartile methods, which can give slightly different values.
• If a result cannot be computed (for example a division by zero, the square root of a negative number, or a factorial of a non-whole number), the calculator says “Cannot compute” rather than showing a misleading number.

4. Checking a result

Every page has a worked example that uses the default numbers and shows each step, so you can repeat the sum on paper or on another calculator. The “Formula used” box lists the exact lines the calculator runs. A small chart shows how the main result changes as the first input moves between half and one and a half times your value, with a table you can open.

5. Limits

A formula is a model. Real materials, people and machines vary, and quantities for building or gardening usually need a waste allowance. Results are estimates for planning and learning, not professional advice; see the disclaimer. We do not publish calculators for medical dosing, loans, tax or investments.

6. Errors and corrections

If a result looks wrong, please send the page address and the numbers you entered through the contact page. Confirmed errors are fixed and listed on the corrections page. A calculator under review can be switched off while it is checked; its formula stays visible.