How do I convert kilometres to miles?

Select the Length category, choose km as the From unit and mi as the To unit, then enter your value. 1 kilometre = 0.621371 miles. You can also click the '1 km → mi' quick preset button.

How do I convert kg to pounds?

Select Weight, choose kg as From and lb as To. 1 kilogram = 2.20462 pounds. Enter any value and the result updates instantly.

Can I convert in both directions?

Yes — you can type in either the From or To field and the other updates automatically. You can also click the swap button to reverse the conversion direction.

What unit systems are supported?

All major metric (SI) and imperial/US customary units are supported across all six categories: length, weight, temperature, speed, area, and volume.

Unit Converter — Length, Weight, Temperature & More

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About the Unit Converter

Unit conversion is a fundamental calculation in science, engineering, cooking, and daily life. The metric system (SI units) is the international standard used in 195 of 197 countries. The US, Myanmar, and Liberia primarily use imperial units, though the UK uses a practical mix: metric for science and most official measurements, imperial for road distances (miles), draught beer (pints), and some everyday weights.

Key conversion factors to remember

Length — 1 inch = 2.54 cm exactly; 1 mile = 1.60934 km; 1 foot = 30.48 cm
Weight — 1 pound = 0.453592 kg; 1 stone = 6.35029 kg; 1 oz = 28.3495 g
Temperature — °C = (°F − 32) × 5/9; °F = °C × 9/5 + 32
Volume — 1 UK pint = 568 mL; 1 US gallon = 3.78541 L; 1 UK gallon = 4.546 L

Why unit conversion accuracy matters

In 1999, NASA lost the Mars Climate Orbiter because one team used metric units and another used imperial — a $327 million error. In aviation, medicine, and engineering, unit conversion errors have caused major incidents. In everyday cooking and baking, getting conversions right makes the difference between a successful recipe and a ruined dish.

SI prefixes and their multipliers

The International System of Units (SI) uses a standard set of prefixes to denote powers of ten. Understanding these prefixes lets you convert between units mentally. The most common: kilo (10^3), mega (10^6), giga (10^9), tera (10^12) for large values; milli (10^-3), micro (10^-6), nano (10^-9), pico (10^-12) for small values.

kilo (k) — 10^3 = 1,000: 1 kilometre = 1,000 metres; 1 kilogram = 1,000 grams
mega (M) — 10^6 = 1,000,000: 1 megabyte = 1,000,000 bytes (SI); 1 MHz = 1,000,000 Hz
giga (G) — 10^9: 1 gigabyte = 1,000 megabytes; 1 GHz = 1,000 MHz
milli (m) — 10^-3: 1 millimetre = 0.001 metres; 1 millisecond = 0.001 seconds

Frequently Asked Questions

How do I convert Celsius to Fahrenheit?

Multiply the Celsius value by 9/5 (or 1.8) and add 32. Formula: F = C x 1.8 + 32. Example: 25C = 25 x 1.8 + 32 = 77F. To convert back: C = (F - 32) / 1.8. Key reference points: 0C = 32F (freezing), 100C = 212F (boiling), 37C = 98.6F (body temperature).

How many centimetres in an inch?

Exactly 2.54 centimetres. This is a defined conversion (not a rounding): 1 inch = 2.54 cm by international agreement since 1959. Therefore 1 foot = 30.48 cm and 1 metre = 39.3701 inches.

What is the difference between UK and US volume measurements?

UK and US pints and gallons are different sizes. A UK pint = 568 mL; a US pint = 473 mL. A UK gallon = 4.546 L; a US gallon = 3.785 L. This matters when comparing fuel economy figures, following American recipes, and buying beverages.

How do I convert kilograms to stone and pounds?

Divide kg by 6.35029 to get stone, then multiply the decimal remainder by 14 to get pounds. Example: 75 kg / 6.35029 = 11.81 stone = 11 stone and 11.4 pounds. Alternatively, multiply kg by 2.20462 to get total pounds, then divide by 14 for stone.

Why does the US still use imperial units?

The US attempted metrication in the 1970s but the Metric Conversion Act of 1975 made it voluntary rather than mandatory. Unlike the UK and Canada, the US never completed the transition. Science, medicine, military, and pharmaceuticals use metric; everyday consumer life uses imperial.