Convert Thou to Millimeters
1 thou is 0.03 mm. One thou is exactly 0.0254 millimeters.
One thou is 0.0254 millimeters. To convert thou to millimeters, multiply by 0.0254; to go the other way, divide by 0.0254 or multiply by 39.370079. The factor is exact rather than rounded: it follows from NIST.
Factor checked against the defining standard · How we check
- Thou × 0.0254
1 * 0.02540.025 mm
1 thou in every length unit
| Unit | Value | Exact factor |
|---|---|---|
| inches | 0.001 in | × 0.001 |
| feet | 0.00008333333333 ft | × 0.0000833333333333 |
| yards | 0.00002777777778 yd | × 0.0000277777777778 |
| miles | 0.00000001578282828 mi | × 0.0000000157828282828 |
| millimeters | 0.0254 mm | × 0.0254 |
| decimetres | 0.000254 dm | × 0.000254 |
| centimeters | 0.00254 cm | × 0.00254 |
| meters | 0.0000254 m | × 0.0000254 |
| kilometers | 0.0000000254 km | × 0.0000000254 |
| nautical miles | 0.00000001371490281 nmi | × 0.0000000137149028078 |
| micrometers | 25.4 µm | × 25.4 |
| nanometers | 25,400 nm | × 25,400 |
| thou (as entered) | 1 thou | — |
Factors are entered by hand from NIST rather than derived from a units library, so the ones that terminate are exact rather than rounded.
The same converter answers this pair however it is written: thou to millimetres is the British spelling of the same units — the metre and the litre are spelled that way outside the United States and the quantity does not change.
How do you convert thou to millimeters? The converter and the working
- 1.Take the measurement in thou.
- 2.Multiply by 0.0254 — that is how many millimeters fit in one thou.
- 3.To go back the other way, divide by 0.0254, or multiply by 39.370079.
Worked example: 25 thou to millimeters
- Formula
- thou × 0.0254 = mm
- Arithmetic
- 25 × 0.0254 = 0.64 mm
- Answer
- 25 thou = 0.64 mm
The factor is exact, so this figure is exact too — only the display is rounded.
Thou to millimeters conversion table
| Thou | Millimeters |
|---|---|
| 1 thou | 0.03 mm |
| 2 thou | 0.05 mm |
| 3 thou | 0.08 mm |
| 4 thou | 0.1 mm |
| 5 thou | 0.13 mm |
| 6 thou | 0.15 mm |
| 7 thou | 0.18 mm |
| 8 thou | 0.2 mm |
| 9 thou | 0.23 mm |
| 10 thou | 0.25 mm |
| 12 thou | 0.3 mm |
| 15 thou | 0.38 mm |
| 20 thou | 0.51 mm |
| 25 thou | 0.64 mm |
| 50 thou | 1.27 mm |
| 100 thou | 2.54 mm |
| 200 thou | 5.08 mm |
| 300 thou | 7.62 mm |
| 500 thou | 12.7 mm |
| 1000 thou | 25.4 mm |
| 2000 thou | 50.8 mm |
| 5000 thou | 127 mm |
| 10000 thou | 254 mm |
A mil is a thousandth of an inch, except where it means a millimeter
In an American workshop a mil is 0.001 in — 25.4 micrometers — and the same drawing read in Europe may be taken as a millimeter, forty times larger. The unambiguous word is thou. Plastic film, plating thickness and printed-circuit copper are all specified in it, and the ambiguity is why exported drawings usually state micrometers instead.
NIST Handbook 44, Appendix C — general tables of units of measurement
What is a thou?
A thousandth of an inch, exactly 25.4 micrometers, and called a mil in American workshops — the same word the metric world uses for a millimeter, which is why a drawing marked "5 mil" is worth checking twice.
What is a millimeter?
One thousandth of a meter. The working unit of metric engineering drawings, which avoid decimals by using it throughout.
How many millimeters are in a thou?
One thou is 0.0254 millimeters, exactly. Going the other way, one millimeter is 39.370079 thou. Both figures come from the same defined relation rather than from a measurement, which is why they are the same today as they were in 1959.
Every length unit here
The whole group — 13 units with their symbols and the size of each one in meters — is on the conversion index, along with every pair it makes. The table above already gives each of them relative to a thou.
Source: NIST — international yard and pound agreement (inch = 25.4 mm exactly)
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Questions people actually ask
- How many millimeters are in a thou?
- 0.0254. One thousandth of a meter. The working unit of metric engineering drawings, which avoid decimals by using it throughout.
- How do I convert millimeters back to thou?
- Divide by 0.0254, or multiply by 39.370079 — they are the same operation.
Other length conversions
Millimeters to thou — the same conversion the other way.