Convert Turns per Inch to Turns per Meter (TPI to TPM)
1 turn per inch (TPI) = 39.37007874 turns per metre (TPM). 1 TPM = 0.0254 TPI. Example: 16.1 TPI = 16.1 × 39.37007874 = 633.8582677 TPM.
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1 TPI = 39.37007874 TPM
Type in either box. Scientific notation works: 1.5e-3.
Converting a list? Use the bulk turn per inch to turn per metre converter to paste a column from Excel.
How to Convert Turn per Inch to Turn per Meter
- 1 TPI = 39.37007874 TPM
- 1 TPM = 0.0254 TPI
- Example: convert 16.1 TPI to TPM: 16.1 TPI = 16.1 × 39.37007874 TPM = 633.8582677 TPM
Formula
TPM = TPI × 39.37007874016
Derivation from SI units:
- 1 TPI = 1 turn per 0.0254 m = 39.37007874 TPM (exact)
- The SI-based unit of twist: complete turns of the yarn about its axis per metre of length.
Both units are defined exactly, so the factor is exact. Turn per Inch definition: turn per inch; Turn per Meter definition: turn per metre.
Worked examples
- A 20s cotton yarn with 16.1 TPI has 633.8582677 TPM.
16.1 TPI × 39.37007874 = 633.8582677 TPM - A hosiery yarn at 12 TPI has 472.4409449 TPM.
12 TPI × 39.37007874 = 472.4409449 TPM
Turn per Inch to Turn per Meter conversion table
| Turns per Inch (TPI) | Turns per Meter (TPM) |
|---|---|
| 3 TPI | 118.1102362 TPM |
| 5 TPI | 196.8503937 TPM |
| 8 TPI | 314.9606299 TPM |
| 10 TPI | 393.7007874 TPM |
| 12 TPI | 472.4409449 TPM |
| 15 TPI | 590.5511811 TPM |
| 16.1 TPI | 633.8582677 TPM |
| 18 TPI | 708.6614173 TPM |
| 20 TPI | 787.4015748 TPM |
| 25 TPI | 984.2519685 TPM |
Where it's used
Cotton-system twist in turns per inch is converted to turns per metre for metric spinning specifications, twist testers and the metric twist multiplier. Multiply by 39.37.
Turn per Inch to other yarn twist units
| Conversion | 1 TPI equals |
|---|---|
| turn per inch to turn per metre | 39.37007874 TPM |
| turn per inch to turn per centimetre | 0.3937007874 TPcm |
| turn per inch to turn per foot | 12 TPF |
Frequently asked questions
How do I convert TPI to TPM?
Multiply by 39.3701, because an inch is exactly 0.0254 m: 16.1 TPI = 633.8582677 TPM.
What is the twist multiplier from TPI?
TM = TPI ÷ √Ne. A 20s yarn with 16.1 TPI has TM = 3.6, a typical hosiery twist.
How many turns per metre are in 1 turn per inch?
1 TPI = 39.37007874 TPM.
How do I convert turns per inch to turns per metre?
Multiply the value in TPI by 39.37007874. For example, 16.1 TPI × 39.37007874 = 633.8582677 TPM.
Is the TPI to TPM conversion exact?
Yes. Both units are defined exactly, so the ratio is exact; its decimal form does not terminate and is shown here to 10 significant figures (more with the precision selector).
Sources
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "inch".
- ISO 1144, Textiles — Universal system for designating linear density (Tex System), International Organization for Standardization , Metric designation of yarn twist.
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Convert Turns per Inch to Turns per Meter (TPI to TPM). Retrieved October 25, 2026, from https://scientificconverters.com/yarn-twist/turns-per-inch-to-turns-per-meter/
IEEE
Scientific Converters, "Convert Turns per Inch to Turns per Meter (TPI to TPM)," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/yarn-twist/turns-per-inch-to-turns-per-meter/