How do I convert millimeters to microinches?
There are about 39,370.08 microinches in a millimetre, so multiply by that. A millimetre is 1/25.4 of an inch and an inch is a million microinches, so the factor is 1,000,000 ÷ 25.4.
0.01 mm is about 394 µin. The other direction is tidier: a microinch is exactly 0.0000254 mm, or 25.4 nanometres.
The two meet on surface-finish drawings, where a metric Ra of 0.8 µm is usually given as 32 µin, near enough.
What is a millimeter?
A millimeter is a thousandth of a meter (1/1000) which is the SI (International System of Units) unit of length. It is normally used to measure small lengths like the thickness of a sheet of paper or the dimensions of a small object.
One millimeter is approximately equal to 0.03937 inches (about 1/25th). Presicely there are 25.4 millimeters in an inch and it is often used in science and engineering. It is used in countries that have adopted the metric system.
You may come across millimeters when measuring the size of electronic components, jewelry or even the thickness of a fingernail.
What is a microinch?
A microinch (µin) is the inch with the SI prefix micro, meaning one millionth, so 1,000,000µin make one inch.
The microinch is mostly seen in surface finish. US drawings give a part's roughness (Ra) in microinches, and a typical machined finish is 63µin, or 1.6µm.
A microinch is a millionth of an inch, which is exactly 0.0254 micrometers or 25.4 nanometers. Outside the US surface finish is given in micrometers instead.