Convert Thou to Micrometers
1 thou is 25.4 µm. One thou is exactly 25.4 micrometers.
One thou is 25.4 micrometers. To convert thou to micrometers, multiply by 25.4; to go the other way, divide by 25.4 or multiply by 0.039370079. The factor is exact rather than rounded: it follows from NIST.
Factor checked against the defining standard · How we check
- Thou × 25.4
1 * 25.425.4 µm
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 micrometres 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 micrometers? The converter and the working
- 1.Take the measurement in thou.
- 2.Multiply by 25.4 — that is how many micrometers fit in one thou.
- 3.To go back the other way, divide by 25.4, or multiply by 0.039370079.
Worked example: 25 thou to micrometers
- Formula
- thou × 25.4 = µm
- Arithmetic
- 25 × 25.4 = 635 µm
- Answer
- 25 thou = 635 µm
The factor is exact, so this figure is exact too — only the display is rounded.
Thou to micrometers conversion table
| Thou | Micrometers |
|---|---|
| 1 thou | 25.4 µm |
| 2 thou | 50.8 µm |
| 3 thou | 76.2 µm |
| 4 thou | 101.6 µm |
| 5 thou | 127 µm |
| 6 thou | 152.4 µm |
| 7 thou | 177.8 µm |
| 8 thou | 203.2 µm |
| 9 thou | 228.6 µm |
| 10 thou | 254 µm |
| 12 thou | 304.8 µm |
| 15 thou | 381 µm |
| 20 thou | 508 µm |
| 25 thou | 635 µm |
| 50 thou | 1,270 µm |
| 100 thou | 2,540 µm |
| 200 thou | 5,080 µm |
| 300 thou | 7,620 µm |
| 500 thou | 12,700 µm |
| 1000 thou | 25,400 µm |
| 2000 thou | 50,800 µm |
| 5000 thou | 127,000 µm |
| 10000 thou | 254,000 µm |
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 micrometer?
A millionth of a meter, still widely called a micron. Machining tolerances, filter ratings and cell diameters are all quoted here.
How many micrometers are in a thou?
One thou is 25.4 micrometers, exactly. Going the other way, one micrometer is 0.039370079 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)
Cite this page
- APA
- Rule Calculator. (2026). Convert Thou to micrometers. Rule Calculator. https://rulecalculators.com/convert/thou-to-micrometer
- MLA
- "Convert Thou to micrometers." Rule Calculator, August 16, 2026, https://rulecalculators.com/convert/thou-to-micrometer.
- Chicago
- Rule Calculator. "Convert Thou to micrometers." Rule Calculator. Last reviewed August 16, 2026. https://rulecalculators.com/convert/thou-to-micrometer.
The date is when the figures on this page were last checked against their source, not the day you opened it. Add your own access date if your style needs one.
Questions people actually ask
- How many micrometers are in a thou?
- 25.4. A millionth of a meter, still widely called a micron. Machining tolerances, filter ratings and cell diameters are all quoted here.
- How do I convert micrometers back to thou?
- Divide by 25.4, or multiply by 0.039370079 — they are the same operation.
Other length conversions
Micrometers to thou — the same conversion the other way.