About This Unit Converter

This tool converts between the most commonly needed units of length, weight, and temperature — the three categories people search for most often in everyday life, cooking, DIY, travel, and international communication. Every conversion runs instantly in your browser using precise conversion factors.

Length Conversions

Length units covered include millimetres, centimetres, metres, kilometres, inches, feet, yards, and miles. The core relationship to remember: 1 inch = 2.54 cm exactly (this is the internationally defined exact conversion), 1 foot = 30.48 cm, 1 mile = 1.60934 km. These conversions matter constantly for anyone working between metric-using countries (most of the world, including Finland and Sweden) and imperial-using countries (primarily the United States, with the UK using a mix of both systems in everyday life).

Weight Conversions

Weight units covered include grams, kilograms, ounces, pounds, and stones. 1 kilogram = 2.20462 pounds, 1 pound = 453.592 grams, 1 stone (used mainly in the UK and Ireland for body weight) = 14 pounds = 6.35 kg. Cooking recipes from different countries frequently use different weight units, making quick conversion essential for following international recipes accurately.

Temperature Conversions

Temperature conversion works differently from length and weight because it isn't a simple multiplication — it involves an offset. Celsius to Fahrenheit: °F = (°C × 9/5) + 32. Fahrenheit to Celsius: °C = (°F − 32) × 5/9. Celsius to Kelvin: K = °C + 273.15. The United States uses Fahrenheit for everyday temperature; nearly every other country, including Finland and Sweden, uses Celsius. Kelvin is used primarily in scientific contexts since it starts at absolute zero.

Frequently Asked Questions

Why is 1 inch defined as exactly 2.54 cm?

This exact relationship was formally established by international agreement in 1959 (the International Yard and Pound Agreement), standardising the previously slightly inconsistent imperial measurements used across different English-speaking countries into an exact metric equivalent.

What's the difference between a UK stone and other weight units?

The stone is a unit historically used across the British Isles, still commonly used in the UK and Ireland for expressing body weight (e.g., "12 stone 4" rather than kilograms or pounds alone), though it has largely fallen out of use elsewhere.

Why does temperature conversion need an offset, unlike length or weight?

Celsius and Fahrenheit scales have different zero points — 0°C is the freezing point of water, while 0°F was originally based on a different reference point (a brine solution). Because the scales don't share a common zero, conversion requires both a multiplication (for the different degree sizes) and an addition/subtraction (to align the zero points).