Convert microns to inches, mils and microinches. 1 µm = 0.00003937 in and 1 mil = 25.4 µm. Use it for surface finish callouts (Ra), coating thickness and tolerances that switch between metric and imperial drawings.
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Request a Proposal →Every value below is exact, not rounded from a rule of thumb. The conversion is fixed by definition: 1 inch = 25 400 µm, so 1 µm = 0.0000393701 in. Everything else on this page follows from that one number.
| Micron (µm) | Inch (in) | Mil (0.001 in) | Microinch (µin) | Millimetre (mm) |
|---|---|---|---|---|
| 0.1 µm | 0.000003937 in | 0.003937 mil | 3.94 µin | 0.0001 mm |
| 0.5 µm | 0.000019685 in | 0.019685 mil | 19.69 µin | 0.0005 mm |
| 1 µm | 0.000039370 in | 0.039370 mil | 39.37 µin | 0.001 mm |
| 2 µm | 0.000078740 in | 0.078740 mil | 78.74 µin | 0.002 mm |
| 5 µm | 0.000196850 in | 0.196850 mil | 196.85 µin | 0.005 mm |
| 10 µm | 0.000393701 in | 0.393701 mil | 393.70 µin | 0.010 mm |
| 12.7 µm | 0.000500000 in | 0.500000 mil | 500.00 µin | 0.0127 mm |
| 20 µm | 0.000787402 in | 0.787402 mil | 787.40 µin | 0.020 mm |
| 25 µm | 0.000984252 in | 0.984252 mil | 984.25 µin | 0.025 mm |
| 25.4 µm | 0.001000000 in | 1.000000 mil | 1000.0 µin | 0.0254 mm |
| 50 µm | 0.001968504 in | 1.968504 mil | 1968.5 µin | 0.050 mm |
| 100 µm | 0.003937008 in | 3.937008 mil | 3937.0 µin | 0.100 mm |
| 254 µm | 0.010000000 in | 10.00000 mil | 10000 µin | 0.254 mm |
The confusion in this unit family is almost always the same three mistakes:
1. A “mil” is not a micron. A mil is one thousandth of an inch (0.001 in), which is 25.4 µm — twenty-five times larger. When a drawing says “0.5 mil coating” it means 12.7 µm, not 0.5 µm.
2. A microinch is not a micron either. One microinch is 0.0254 µm. So 32 µin = 0.81 µm. US drawings give surface finish in µin (often written as Ra 32), European and Asian drawings give the same finish in µm (Ra 0.8). A part is not finished to a different standard just because the number changed — it is the same surface.
3. Micron, micrometre and µm are the same unit. “Micron” is simply the older name for a micrometre, one millionth of a metre. There is nothing to convert between them.
Turning gives roughly Ra 0.8–3.2 µm (32–125 µin). Grinding gives Ra 0.1–0.8 µm (4–32 µin). Lapping and honing go below Ra 0.1 µm. If a drawing specifies a finish in µin and your shop works in µm, divide by 39.37 — or read it straight off the table above.
Precision machining lives in microns and tenths. Surface finish is measured in microinches (Ra) in the US and micrometres internationally. Coatings are specified in microns. This converter handles all common precision length units.
In US shops, a tenth means 0.0001 inch (one ten-thousandth), which equals 2.54 microns. "I need to hold plus or minus a tenth" means plus or minus 2.5 microns -- a tight but achievable tolerance with grinding or high-precision turning. Metric shops would say "plus or minus 2 microns."
Turning: Ra 0.8-3.2 um (32-125 uin). Grinding: Ra 0.1-0.8 um (4-32 uin). Lapping: Ra 0.025-0.2 um (1-8 uin). Superfinishing: Ra 0.012-0.1 um (0.5-4 uin). Mirror finish: under Ra 0.025 um (1 uin). The best achievable with diamond turning is about Ra 0.005 um (0.2 uin).
PVD coatings (TiN, AlTiN, TiAlN, TiCN) are typically 2-5 microns (0.00008-0.0002 inch) thick. CVD coatings are thicker at 5-12 microns. Anodising on aluminium: 5-25 microns. Hard chrome plating: 25-100 microns. Zinc electroplating: 5-15 microns.
Enter a value in any of the supported units. The converter shows equivalents in microns, mils, microinches, and millimetres. Use this to compare surface finish specs, coating thicknesses, and precision tolerances across metric and imperial drawings.
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