Convert Thou to Inches
1 thou is 0.001 in. One thou is exactly 0.001 inches.
One thou is 0.001 inches. To convert thou to inches, multiply by 0.001; to go the other way, divide by 0.001 or multiply by 1000. The factor is exact rather than rounded: it follows from NIST.
Factor checked against the defining standard · How we check
- Thou × 0.001
1 * 0.0010.001 in
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.
How do you convert thou to inches? The converter and the working
- 1.Take the measurement in thou.
- 2.Multiply by 0.001 — that is how many inches fit in one thou.
- 3.To go back the other way, divide by 0.001, or multiply by 1000.
Worked example: 25 thou to inches
- Formula
- thou × 0.001 = in
- Arithmetic
- 25 × 0.001 = 0.03 in
- Answer
- 25 thou = 0.03 in
The factor is exact, so this figure is exact too — only the display is rounded.
Thou to inches conversion table
| Thou | Inches |
|---|---|
| 1 thou | 0.001 in |
| 2 thou | 0.002 in |
| 3 thou | 0.003 in |
| 4 thou | 0.004 in |
| 5 thou | 0.01 in |
| 6 thou | 0.01 in |
| 7 thou | 0.01 in |
| 8 thou | 0.01 in |
| 9 thou | 0.01 in |
| 10 thou | 0.01 in |
| 12 thou | 0.01 in |
| 15 thou | 0.02 in |
| 20 thou | 0.02 in |
| 25 thou | 0.03 in |
| 50 thou | 0.05 in |
| 100 thou | 0.1 in |
| 200 thou | 0.2 in |
| 300 thou | 0.3 in |
| 500 thou | 0.5 in |
| 1000 thou | 1 in |
| 2000 thou | 2 in |
| 5000 thou | 5 in |
| 10000 thou | 10 in |
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 an inch?
Exactly 25.4 millimeters since the 1959 international yard and pound agreement, and one twelfth of a foot.
How many inches are in a thou?
One thou is 0.001 inches, exactly. Going the other way, one inch is 1000 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 inches. Rule Calculator. https://rulecalculators.com/convert/thou-to-inch
- MLA
- "Convert Thou to inches." Rule Calculator, August 16, 2026, https://rulecalculators.com/convert/thou-to-inch.
- Chicago
- Rule Calculator. "Convert Thou to inches." Rule Calculator. Last reviewed August 16, 2026. https://rulecalculators.com/convert/thou-to-inch.
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 inches are in a thou?
- 0.001. Exactly 25.4 millimeters since the 1959 international yard and pound agreement, and one twelfth of a foot.
- How do I convert inches back to thou?
- Divide by 0.001, or multiply by 1000 — they are the same operation.
Other length conversions
Inches to thou — the same conversion the other way.