Length Unit Converter

Pipe schedules, cable trays, civil drawings and instrument manuals each quote length in a different unit, and a factor-of-ten or a wrong inch conversion is enough to misthread a fitting or mislay a sensor. This converter moves exactly between metric and imperial length with no approximation.

Convert length unit units

Value

From

Why length units collide

Metric length is decimal and SI-native, while imperial length stacks inches, feet, yards and miles on a base-12 and base-1760 system that predates any standard. Mixing them in one calculation is where the classic off-by-factor errors come from.

All the relations here are exact definitions — 1 in = 25.4 mm, 1 ft = 0.3048 m, 1 mi = 1609.344 m, 1 nmi = 1852 m — so the converter is exact, not rounded. The only discipline needed is carrying the unit with the number.

Which unit where

Millimetres and metres dominate mechanical, piping and panel drawings in metric markets; inches and feet are the language of imperial equipment, conduit and structural specs. Kilometres and miles describe distances and cable routes; the nautical mile belongs to hydraulic and marine positioning.

Complete conversion reference

Convert 1 unit to	m	km	cm	mm	µm	in	ft	yd	mi	nmi
1 m	1	0.001	100	1000	1e+06	39.3701	3.28084	1.09361	0.000621371	0.000539957
1 km	1000	1	100000	1e+06	1e+09	39370.1	3280.84	1093.61	0.621371	0.539957
1 cm	0.01	1e-05	1	10	10000	0.393701	0.0328084	0.0109361	6.21371e-06	5.39957e-06
1 mm	0.001	1e-06	0.1	1	1000	0.0393701	0.00328084	0.00109361	6.21371e-07	5.39957e-07
1 µm	1e-06	1e-09	0.0001	0.001	1	3.93701e-05	3.28084e-06	1.09361e-06	6.21371e-10	5.39957e-10
1 in	0.0254	2.54e-05	2.54	25.4	25400	1	0.0833333	0.0277778	1.57828e-05	1.37149e-05
1 ft	0.3048	0.0003048	30.48	304.8	304800	12	1	0.333333	0.000189394	0.000164579
1 yd	0.9144	0.0009144	91.44	914.4	914400	36	3	1	0.000568182	0.000493737
1 mi	1609.34	1.60934	160934	1.60934e+06	1.60934e+09	63360	5280	1760	1	0.868976
1 nmi	1852	1.852	185200	1.852e+06	1.852e+09	72913.4	6076.12	2025.37	1.15078	1

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Frequently asked

How many millimetres in an inch?

Exactly 25.4 mm. One foot is exactly 0.3048 m (304.8 mm) and one yard is 0.9144 m. These are defined conversions, so the converter returns exact values, not rounded ones.

What is 1 mile in kilometres?

One international mile is 1609.344 m, or 1.609344 km. The nautical mile used in marine and hydraulic work is 1852 m exactly.

Is cm or mm better for instrument drawings?

Millimetres are the convention for mechanical and piping drawings because they avoid decimal confusion; centimetres appear in some consumer and legacy specs. Pick the unit your standard writes in, then convert for shop use.

Why does my drawing use both mm and inches?

A drawing may combine metric structure with imperial components (valves, fittings, sensors bought to inch standards). Convert at the interface rather than mixing units inside one calculation to avoid the classic off-by-ten error.

This page performs exact unit arithmetic with no physical assumption beyond the stated reference (for example mH₂O assumes water near 4 °C, and pH follows its logarithmic definition). It is a working aid, not a substitute for the measurement method named in your permit.