Data & Converters
World Measurement Unit Converter
Convert between metric and imperial units for length, weight, volume and temperature — accurate to the SI definitions.
Result
3.28084 ft
Conversions use standard SI definitions. 1 inch = 25.4 mm exactly.
The metric and imperial divide
The world runs on two measurement systems. The metric system (Système International) is base-10, coherent and official in almost every country — metres, kilograms, litres, Celsius. The imperial system, descended from British units, uses inches, feet, pounds, gallons and Fahrenheit, and is the everyday system in the United States and partly in the United Kingdom.
Travellers between the two worlds constantly convert. A 6-foot sign height, a 200-pound baggage limit, a 65 mph speed limit, a 70°F day — all need conversion when your intuition is metric. This tool handles the arithmetic so you can think in the system you grew up with.
How the conversion math works
Length, weight and volume conversions pass through a single base unit. To convert 5 miles to kilometres, the tool first converts miles to metres (5 × 1609.344 = 8046.72 m) then metres to kilometres (÷ 1000 = 8.047 km). The factors are exact SI definitions — 1 inch is defined as exactly 25.4 millimetres — so the results are exact, not approximate.
Temperature is special because its zero points differ. Celsius to Fahrenheit multiplies by 9/5 and adds 32; Celsius to Kelvin adds 273.15. Fahrenheit to Celsius subtracts 32 then multiplies by 5/9. These are exact under the modern definitions.
Length: the everyday conversions
The length conversions travellers use most are small: inches to centimetres (1 in = 2.54 cm), feet to metres (1 ft = 0.3048 m), and miles to kilometres (1 mi = 1.609 km). A useful set of mental anchors: a metre is about a yard plus a tenth; a mile is about 1.6 km; a foot is about 30 cm.
Height is the most personal conversion — many people know their height in one system and not the other. Six feet is 183 cm; five feet is 152 cm. This tool removes the arithmetic for those everyday cases.
Weight and volume in the kitchen
Recipes cross systems constantly. A US recipe in cups and ounces is opaque to a metric cook; a European recipe in grams is opaque to an American. The exact conversions — 1 cup ≈ 237 ml, 1 ounce ≈ 28.35 g, 1 pound ≈ 453.6 g — let you follow any recipe.
Note the gallon trap: a US gallon is 3.785 litres, but a UK imperial gallon is 4.546 litres. US and UK pints differ too (473 ml vs 568 ml). This tool uses US volumes, the most common online. For a UK recipe, check which gallon is intended.
Temperature: the two scales
Celsius and Fahrenheit meet at -40°, where both scales read the same number. Above that, Fahrenheit numbers are larger; below, Celsius numbers go more negative. Body temperature is 37°C / 98.6°F; a comfortable room is about 20°C / 68°F; water boils at 100°C / 212°F at sea level.
Kelvin is the SI temperature unit, used in science; it shifts Celsius by 273.15 so that zero is absolute zero. Most people never need Kelvin, but it appears in technical and scientific contexts and is included here for completeness.
A practical approach to living between systems
For a short trip, learn a few anchors rather than converting every number. A speed limit in km/h is about six-tenths in mph; a distance in km is about six-tenths in miles; a temperature in Celsius doubled plus 30 approximates Fahrenheit. These rough rules let you estimate instantly, then use this tool for exact figures when it matters.
For longer stays, the goal is to develop intuition in the new system rather than converting constantly — to feel that 20°C is pleasant without translating to 68°F. The tool bridges the gap until your intuition catches up.
Frequently Asked Questions
What is the difference between metric and imperial?
Metric (SI) uses base-10 units (metre, kilogram, litre) and is the official system in almost every country. Imperial (inch, foot, pound, gallon) is used primarily in the United States, and partly in the UK. Liberia and Myanmar also use non-metric systems.
How are conversions calculated?
Length, weight and volume conversions pass through a base unit (metre, kilogram, litre) using exact SI conversion factors. Temperature uses its own formulas: °F = °C × 9/5 + 32; K = °C + 273.15.
Is the imperial gallon the same as the US gallon?
No. The US gallon is 3.785 litres; the imperial (UK) gallon is 4.546 litres. This tool uses the US gallon. For UK gallons, multiply litres by 0.219969.
Why does the US still use imperial?
Historical path dependence: the US adopted British imperial units and never metricated roads and everyday commerce, despite metric being used in science, medicine and much industry. Conversion is a recurring political debate.
Are these conversions exact?
Length, weight and volume conversions here use exact SI definitions (1 inch = 25.4 mm exactly). Temperature is exact. Only a few historical units have non-exact definitions; this tool uses the modern standardised ones.
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