A Quick Reference Guide to Common Unit Conversions

Unit conversions come up constantly — cooking, travel, schoolwork, fitness tracking, DIY projects — and it's easy to mix up a factor when converting by hand, especially between the metric and imperial systems.

Length

1 inch = 2.54 centimeters. 1 foot = 0.3048 meters. 1 yard = 0.9144 meters. 1 mile = 1.609 kilometers. These come up constantly when comparing US and metric measurements for height, room dimensions, or travel distances — a common trip-up is forgetting that a mile is meaningfully longer than a kilometer, which matters if you're estimating travel time from a distance given in the "wrong" unit for your intuition.

Weight and mass

1 pound = 0.4536 kilograms. 1 ounce = 28.35 grams. 1 kilogram = 2.2046 pounds. 1 stone (used in the UK) = 6.35 kilograms. These matter for reading nutrition labels, shipping weights, gym equipment calibrated in pounds vs kilograms, and recipes sourced from a different country's cookbook.

Volume

1 liter = 0.2642 US gallons. 1 US gallon = 3.785 liters. 1 US cup = 236.6 milliliters — though note the UK/imperial cup and gallon are different sizes from the US versions, which is a common source of recipe conversion errors when following a UK source with US measuring cups, or vice versa.

Temperature

Temperature conversion isn't a simple multiplication like the others — Celsius to Fahrenheit is (°C × 9/5) + 32, and Fahrenheit to Celsius is (°F − 32) × 5/9. Kelvin is Celsius plus 273.15, and is mostly used in scientific and engineering contexts rather than everyday weather reporting. A quick sanity check: 0°C (freezing) is 32°F, and 100°C (boiling, at sea level) is 212°F — if a conversion doesn't land near those reference points, it's worth double-checking the formula.

A quick mental-math shortcut

For a rough Celsius-to-Fahrenheit estimate without doing the full formula, doubling the Celsius value and adding 30 gets close enough for everyday use — 20°C roughly becomes 70°F (the precise answer is 68°F). It's not exact, but it's usually close enough to decide whether you need a jacket.

Other units worth knowing about

Length, weight, volume, and temperature cover most everyday conversions, but a few specialized categories are common enough to deserve their own dedicated tools rather than a quick mental formula. Converting speed between km/h, mph, and knots comes up for travel and vehicles — the Speed Converter handles that directly. Converting between bytes, megabytes, gigabytes, and terabytes matters for anything involving file sizes or storage plans — the Data Storage Converter covers both the decimal and binary versions of those units, which aren't quite the same number.

Skip the mental math

Instead of memorizing conversion factors or risking an arithmetic mistake under time pressure, use the Unit Converter to convert between length, weight, and temperature units instantly, with the precision already built in.