Explanation
Metric and imperial lengths
Pick the unit you measured in and the unit you need. Metric units step by powers of ten; inches, feet, yards and miles are fixed multiples of the metre, so every conversion is a single exact factor.
y = x × k
| x | value in the unit you convert from |
|---|---|
| k | conversion factor: metres per source unit ÷ metres per target unit |
| y | value in the unit you convert to |
1 inch to metres
| Value | 1 |
|---|---|
| From | Inches (in) |
| To | Metres (m) |
| Result | 0.0254 m |
1 in = 0.0254 m
3 feet to metres
| Value | 3 |
|---|---|
| From | Feet (ft) |
| To | Metres (m) |
| Result | 0.9144 m |
3 ft = 0.9144 m
1 mile to kilometres
| Value | 1 |
|---|---|
| From | Miles (mi) |
| To | Kilometres (km) |
| Result | 1.609344 km |
1 mi = 1.609344 km
Diagram of this result
The marker shows the entered length on a ruler in the source unit; the ruler below it is drawn in the target unit at the same scale, so the reading under the marker is the answer.
The answer and the steps state both values with their unit symbols.
Definitions and limits
An international inch is exactly 0.0254 m, so a foot is exactly 0.3048 m and a mile exactly 1,609.344 m. The older US survey foot is not offered. Answers are shown to six significant figures; the calculation keeps every digit.
Common mistakes
Length is not area: one metre is 3.28 feet, but one square metre is 10.76 square feet. Do not round a factor such as 2.54 before multiplying a large number. A negative value is treated as an offset in the opposite direction.
How many centimetres are in an inch?
Exactly 2.54 cm. The inch has been defined as 25.4 mm since 1959, so 12 inches are 30.48 cm and 3 feet are 0.9144 m.
References
NIST SP 811, Guide for the Use of the International System of Units, including its conversion factors: https://www.nist.gov/pml/special-publication-811.