Length & Distance Converter

The conversions people actually need

From	To	Multiply by	Example
Inches	Centimetres	2.54	12 in = 30.48 cm
Centimetres	Inches	0.393701	30 cm = 11.81 in
Feet	Metres	0.3048	6 ft = 1.8288 m
Metres	Feet	3.28084	2 m = 6.5617 ft
Miles	Kilometres	1.609344	26.2 mi = 42.16 km
Kilometres	Miles	0.621371	100 km = 62.14 mi
Yards	Metres	0.9144	100 yd = 91.44 m

Every factor in that table is exact, not rounded — which is worth explaining, because it is unusual.

Why these numbers are exact

Most conversion factors in science are measurements, and measurements have error bars. These do not.

In 1959, the United States, United Kingdom, Canada, Australia, New Zealand and South Africa signed the international yard and pound agreement, which defined the yard as exactly 0.9144 metres. Everything else follows by arithmetic:

• 1 yard = 0.9144 m, exactly
• 1 foot = ⅓ yard = 0.3048 m, exactly
• 1 inch = 1⁄36 yard = 0.0254 m, exactly
• 1 mile = 1,760 yards = 1,609.344 m, exactly

So “2.54 centimetres to the inch” is not an approximation anyone measured. It is what an inch is. A converter that uses 2.5, or rounds the mile to 1,609 metres, is introducing an error that did not need to exist.

Converting in your head

• Centimetres to inches: divide by 2.5 and take a little off. 100 cm ÷ 2.5 = 40, and the true answer is 39.4.
• Kilometres to miles: take five-eighths. Half, plus an eighth. 80 km → 40 + 10 = 50 miles, against a true 49.7.
• Metres to feet: multiply by 3 and add 10%. 10 m → 30 + 3 = 33 feet, against 32.8.
• Fibonacci trick: consecutive Fibonacci numbers are roughly km and miles. 5 km ≈ 3 mi, 8 km ≈ 5 mi, 13 km ≈ 8 mi. It works because the golden ratio, 1.618, is close to 1.609.

Human heights

The conversion people look up most often:

Feet and inches	Centimetres
5’0”	152.4
5’2”	157.48
5’4”	162.56
5’6”	167.64
5’8”	172.72
5’10”	177.8
6’0”	182.88
6’2”	187.96

To do it yourself: multiply the feet by 12, add the inches, multiply by 2.54. So 5’9” is (5 × 12 + 9) × 2.54 = 69 × 2.54 = 175.26 cm.

The units that are not what they seem

• The nautical mile is 1,852 metres, not 1,609. It was defined as one minute of latitude, which is why it suits navigation — and it is why a knot (one nautical mile per hour) is faster than a mile per hour.
• The US survey foot was very slightly longer than the international foot, used for land surveying, and officially retired at the end of 2022. Over a long boundary the difference amounted to real distance.
• The metre itself is now defined by the speed of light — the distance light travels in 1⁄299,792,458 of a second. Every other unit on this page is ultimately defined in terms of that.