Length Converter
Convert mm, cm, m, km, inches, feet, yards, and miles with exact factors.
What it does
Length conversion is multiplication by a fixed factor. The meter anchors the metric side, and the inch anchors the imperial side at exactly 2.54 centimeters by international agreement since 1959. Every other unit follows from those two definitions.
The tool above converts between eight units: millimeters, centimeters, meters, kilometers, inches, feet, yards, and miles. Pick the source and target, enter the value, and the answer updates at once, with all eight equivalents listed below it.
For craft and trade work, mind rounding. Converting 5 miles to kilometers gives 8.04672, and cutting that to 8.05 is fine for a run but not for machining, where the missing 3.28 mm matters.
How to use
- Enter the value in the source unit.
- Pick the source unit on the left and the target on the right.
- Read the converted line, then scan the all units note for the rest.
- Round only the final number, never the middle of a chain of conversions.
Formula
- 0.0254
- Meters in one inch, exact.
- 1609.344
- Meters in one mile, exact.
- meters first
- Single hub so all pairs need one path.
Going through meters keeps one path for all pairs instead of memorizing dozens of ratios. The inch factor of 0.0254 is exact by definition, so metric to imperial results carry full precision until you round.
Worked example
Example: 5 miles to kilometers
Value 5, from miles, to kilometers.
- Meters first: 5 x 1609.344 = 8046.72 m.
- Divide by the target factor: 8046.72 / 1000 = 8.04672 km.
- Result: 5 mi = 8.04672 km.
- Check back: 8.04672 x 1000 / 1609.344 = 5.00000 mi.
Reference table
| Pair | Factor | Everyday check |
|---|---|---|
| 1 in to cm | 2.54 (exact) | A phone width near 3 in is 7.62 cm |
| 1 ft to m | 0.3048 (exact) | 6 ft is 1.8288 m |
| 1 yd to m | 0.9144 (exact) | 100 yd is 91.44 m |
| 1 mi to km | 1.609344 (exact) | 5 mi is 8.04672 km |
| 1 km to mi | 0.621371 | 10 km is 6.21371 mi |
Limits
- Length only. Area and volume square or cube the factor.
- Survey feet on old land records differ slightly.
- Nautical miles are separate: 1852 m each.
- Precision work needs calibrated tools, not conversions.
Common mistakes
- Using 2.5 for the inch instead of 2.54, which drifts 1.6% on every conversion.
- Rounding mid chain across several steps instead of once at the end.
- Mixing US survey feet with international feet on land records. For everyday use the international foot here is right.
- Reading fluid ounces or square units into a length problem.
- Trusting a rounded factor from memory for precision work.
Try it yourself
Quick checks. Answers sit tucked under each question.
100 cm in inches?
100 / 2.54 = about 39.37 in.
1 km in miles?
1 / 1.609344 = 0.6214 mi.
Questions
How many cm are in an inch?
Exactly 2.54 cm. This value is fixed by international agreement, not measured fresh each time.
How many feet are in a meter?
About 3.28084 ft. The exact path is 1 / 0.3048.
What is 5 ft 9 in in cm?
69 inches times 2.54 equals 175.26 cm.
Is a mile 1.6 km?
Close: exactly 1.609344 km. The 1.6 shortcut drifts 9 meters per mile.
Which unit should I keep for building work?
Millimeters for cutting lists, since whole millimeters round less than centimeters with decimals.