How many centimeters are in an inch?

Exactly 2.54 — this has been the legal definition of the inch since 1959, not a rounded value. So 1 foot is exactly 30.48 cm and 1 yard is exactly 91.44 cm.

How do I convert kilograms to pounds?

Multiply by 2.2046 (1 kg = 2.20462 lb). Going the other way, 1 pound is exactly 0.45359237 kg. For head math, "kilos times two plus 10%" gets you within a percent.

Why are US and UK gallons different?

The US kept the older English wine gallon (231 cubic inches, 3.785 liters) when it standardised its units, while Britain redefined the imperial gallon in 1824 as 4.546 liters. Everything built on them — pints, quarts, fluid ounces — differs between the two systems as a result.

Is a metric tonne the same as a ton?

No. A metric tonne is 1,000 kg (about 2,204.6 lb). A US "short ton" is 2,000 lb (907.2 kg) and a British "long ton" is 2,240 lb (1,016 kg). If a source just says "ton", check which one it means — the spread is over 10%.

Measurement

Unit Conversion Chart

LK Forge · 4 min read · Updated July 2026

These tables cover the conversions people actually look up: metric ↔ imperial for length, weight, volume, temperature, area and speed. Factors marked exact are legal definitions, not approximations; everything else is rounded to a practical number of digits. For a specific value, the unit converter computes it live.

Length

Imperial → Metric	Metric → Imperial
1 inch = 2.54 cm (exact)	1 cm = 0.3937 in
1 foot = 0.3048 m (exact)	1 m = 3.2808 ft
1 yard = 0.9144 m (exact)	1 m = 1.0936 yd
1 mile = 1.609344 km (exact)	1 km = 0.6214 mi

Try it on a real number: miles → km, km → miles or cm → inches.

Weight & mass

Imperial → Metric	Metric → Imperial
1 ounce = 28.3495 g	1 gram = 0.0353 oz
1 pound = 0.45359237 kg (exact)	1 kg = 2.20462 lb
1 stone (14 lb) = 6.3503 kg	1 kg = 0.1575 st
1 US short ton (2,000 lb) = 907.185 kg	1 tonne (1,000 kg) = 2,204.62 lb

Converters: kg → lbs and lbs → kg.

Volume

Volume is where the US and UK systems split — note which gallon you need.

US unit	Metric
1 teaspoon	4.929 mL
1 tablespoon	14.787 mL
1 fluid ounce	29.574 mL
1 cup (8 fl oz)	236.6 mL
1 pint	473.2 mL
1 quart	0.9464 L
1 gallon	3.7854 L

UK (imperial) unit	Metric
1 imperial fluid ounce	28.413 mL
1 imperial pint	568.26 mL
1 imperial gallon = 4.54609 L (exact)	1 L = 0.22 imp gal

Going the other way: 1 liter = 33.814 US fl oz = 0.2642 US gallons. Convert any amount with gallons → liters or liters → gallons.

Temperature

Conversion	Formula
Celsius → Fahrenheit	°F = °C × 9/5 + 32
Fahrenheit → Celsius	°C = (°F − 32) × 5/9
Celsius → Kelvin	K = °C + 273.15

°C	°F	Reference point
−40	−40	the scales meet
0	32	water freezes
37	98.6	body temperature
100	212	water boils (at sea level)

Live conversion: °C → °F and °F → °C.

Area

Imperial → Metric	Metric → Imperial
1 sq inch = 6.4516 cm² (exact)	1 m² = 10.764 sq ft
1 sq foot = 0.0929 m²	1 m² = 1.196 sq yd
1 acre = 0.4047 hectares	1 hectare = 2.4711 acres
1 sq mile = 2.59 km²	1 km² = 0.3861 sq mi

Speed

Unit	Equivalents
1 mph	1.609344 km/h (exact)
1 knot	1.852 km/h (exact) = 1.1508 mph
1 m/s	3.6 km/h (exact) = 2.2369 mph
100 km/h	62.14 mph

Common pairs: mph → km/h and km/h → mph.

Wondering why two systems exist at all — and why the US never switched? That story is in Metric vs Imperial: What's the Difference?

Need an exact answer for a specific number? The converter does the math live as you type.

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