How conversions work
Every category here is anchored to one base unit — meters for length, kilograms for weight, liters for volume, kilometers per hour for speed, and square meters for area. Each unit stores a fixed factor stating how many base units it equals. Converting takes two steps: your value is multiplied by the "from" factor to reach the base unit, then divided by the "to" factor. Temperature works differently because Celsius, Fahrenheit, and Kelvin are connected by offset equations rather than clean ratios, so dedicated formulas handle those pairs.
Length — travel, DIY, and sport
Road signs abroad, furniture listings, and race distances all mix systems: a marathon is 42.195 km, a mile is exactly 1.609344 kilometers, and an inch is 2.54 cm. Convert ft to cm before buying furniture from overseas, or km to mi when planning a road trip.
Weight — kitchen and shipping
Recipes jump between grams and ounces, airlines cap checked bags at 23 kg (50 lb), and couriers bill by the pound. One kilogram equals 2.20462 pounds, one pound is 453.59 grams, and one stone is 6.35 kg.
Temperature — weather, ovens, and science
To convert C to F, multiply by 9⁄5 and add 32 — 20 °C becomes 68 °F. Ovens marked 180 °C correspond to 350 °F in American recipes. Kelvin, used in science, starts at absolute zero: −273.15 °C.
Volume — cooking cups and mL
American recipes measure in cups while packaging lists milliliters: 1 US cup is 236.59 mL, 1 US pint is 473.18 mL, and 1 US gallon is 3.785 L. Watch out for imperial units — a UK gallon is 4.546 L, roughly 20% larger than a US gallon. This tool uses US gallons throughout.
Speed — pace and driving
Treadmills often show km/h while GPS watches log mph: 100 km/h is 62.14 mph on a highway dial. Sailors and pilots use knots — 1 knot is 1.852 km/h, handy for checking wind forecasts.
Area — real estate and land
Listings quote m² in Europe and ft² in the US: 1 m² equals 10.7639 ft², so an 80 m² apartment is about 861 ft². For land, an acre covers 4,046.86 m² and a hectare is exactly 10,000 m².