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Unit Converter — Free Online Measurement Converter

The metric and imperial systems coexist across every area of daily life — road signs, recipes, product labels, weather forecasts, clothing sizes, luggage allowances. This free unit converter handles six categories with 43 units and 294 possible conversions. Type in either field and the other updates instantly.

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Length Conversions

  • 1 kilometre = 0.621371 miles
  • 1 mile = 1.60934 kilometres
  • 1 foot = 0.3048 metres
  • 1 metre = 3.28084 feet
  • 1 inch = 2.54 centimetres
  • 1 yard = 0.9144 metres

Real world anchors:

  • A standard door: 2 metres = 6 feet 7 inches
  • A marathon: 42.195 km = 26.219 miles
  • A football pitch: approximately 100 metres = 109 yards
  • An A4 sheet: 297mm × 210mm = 11.7in × 8.3in

Weight Conversions

  • 1 kilogram = 2.20462 pounds
  • 1 pound = 0.453592 kilograms
  • 1 stone = 6.35029 kilograms = 14 pounds
  • 1 ounce = 28.3495 grams
  • 1 tonne = 1,000 kilograms = 2,204.62 pounds

Real world anchors:

  • Average adult: 70 kg = 154 lbs = 11 stone
  • Standard airline carry-on: 7 kg = 15.4 lbs
  • A litre of water weighs exactly 1 kilogram
  • A US pound of butter = 454 grams

Temperature Conversions

Temperature is the one category where a simple multiplication factor does not work — the scales have different zero points, so every conversion requires a formula.

Celsius to Fahrenheit: °F = (°C × 9/5) + 32

Fahrenheit to Celsius: °C = (°F − 32) × 5/9

Celsius to Kelvin: K = °C + 273.15

Temperature

Celsius

Fahrenheit

Kelvin

Absolute zero

−273.15°C

−459.67°F

0 K

Water freezes

0°C

32°F

273.15 K

Normal body temp

37°C

98.6°F

310.15 K

Water boils

100°C

212°F

373.15 K

Oven — moderate

180°C

356°F

453.15 K

Speed Conversions

  • 1 km/h = 0.621371 mph
  • 1 mph = 1.60934 km/h
  • 1 m/s = 3.6 km/h
  • 1 knot = 1.852 km/h
  • Mach 1 = 1,235 km/h = 767 mph (at sea level, 20°C)

Common speed limits converted:

km/h

mph

Common use

30 km/h

18.6 mph

Residential zones

50 km/h

31 mph

Urban roads

80 km/h

49.7 mph

Rural roads

100 km/h

62.1 mph

Motorways (metric countries)

120 km/h

74.6 mph

Motorways (some countries)

70 mph

112.7 km/h

UK motorway limit

Volume Conversions

  • 1 litre = 0.264172 US gallons
  • 1 US gallon = 3.78541 litres
  • 1 UK gallon = 4.54609 litres
  • 1 US cup = 236.588 mL
  • 1 UK pint = 568.261 mL
  • 1 US pint = 473.176 mL
  • 1 fluid ounce = 29.5735 mL

Real world anchors:

  • A standard wine bottle = 750 mL
  • A standard bathtub holds approximately 150 litres
  • 1 US cup ≈ the size of a standard mug
  • A standard can of soft drink = 330 mL (EU) or 355 mL (US)

Important: US and UK volume measurements differ significantly. A US gallon is about 20% smaller than a UK gallon. A US pint is about 17% smaller than a UK pint. Always check which system a recipe uses before converting.

Area Conversions

  • 1 acre = 4,046.86 m²
  • 1 hectare = 10,000 m² = 2.471 acres
  • 1 square mile = 2.59 km² = 640 acres
  • 1 square foot = 0.0929 m²
  • 1 square metre = 10.7639 sq ft

Real world anchors:

  • A standard football pitch: ≈ 0.71 hectares = 1.76 acres
  • A tennis court: 260.87 m² = 2,808 sq ft
  • A standard UK building plot: approximately 0.1 acres = 404 m²
  • Central Park, New York: 341 hectares = 843 acres

Metric vs Imperial — Which Countries Use Which?

Only three countries have not officially adopted the metric system — the United States, Liberia and Myanmar. Every other country uses metric (SI units) for official purposes.

The United Kingdom officially uses metric but retains miles for road distances, pints for beer and milk, and stones for body weight — a hybrid system that requires frequent conversion. This is why a British person reading a US recipe, checking a European speed limit or buying clothes online from Asia regularly needs a unit converter for everyday tasks.

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Frequently Asked Questions

Multiply kilometres by 0.621371. For example 100 km × 0.621371 = 62.1 miles. Quick mental shortcut — multiply by 0.6 for an approximate answer. 5 miles ≈ 8 km is a commonly used approximation.

Multiply kilograms by 2.20462. For example 70 kg × 2.20462 = 154.3 lbs. Quick mental shortcut — multiply by 2.2. For stones divide the kg value by 6.35.

Multiply the Celsius value by 9/5 (1.8) then add 32. For example 20°C × 1.8 + 32 = 68°F. A rough mental shortcut — double the Celsius value and add 30 for an approximate result. Use the Temperature tab in the unit converter above for the exact figure.

1 mile = 1.60934 kilometres exactly. For quick mental maths multiply miles by 1.6. So 5 miles ≈ 8 km and 10 miles ≈ 16 km.

A US gallon = 3.785 litres. A UK Imperial gallon = 4.546 litres — about 20% larger. This difference matters for fuel economy comparisons. A car rated at 30 mpg in the UK would be rated at approximately 25 mpg in the US for the same actual fuel consumption.

Mach 1 — the speed of sound — is approximately 1,235 km/h or 767 mph at sea level at 20°C. The speed of sound decreases with altitude as air becomes colder and thinner — a commercial aircraft flying at cruising altitude experiences Mach 1 at around 1,062 km/h.

1 metre = 3.28084 feet. 1 foot = 0.3048 metres exactly. Quick mental reference — 1 metre is approximately 3 feet 3 inches.

1 stone = 6.35029 kilograms = 14 pounds. Stones are used almost exclusively in the UK and Ireland for body weight. 11 stone = 69.85 kg = 154 lbs.

About This Unit Converter

This unit converter is part of CalcDaysTime — a free suite of date, time and maths tools. All conversions run entirely in your browser using precise conversion factors. No data is sent to our servers, stored or shared with anyone.

Disclaimer: Conversion factors are based on internationally accepted standards. For scientific or engineering applications requiring maximum precision always verify against official standards such as NIST or BIPM publications.