Turn per Inch (TPI)
Turns per inch (TPI) is the twist count of the cotton system. With English count Ne, the twist multiplier is TM = TPI ÷ √Ne; hosiery yarns use about 3.2–3.6 and warp yarns 4–4.5.
Symbol: TPI
Quantity: yarn twist (turns per unit length)
SI relation: 1 TPI = 39.37007874016 TPM (exact)
Derivation: 1 TPI = 1 turn per 0.0254 m = 39.37007874 TPM (exact)
Exact: yes, by definition
Typical uses
- Cotton-system spinning (ring, rotor) and twist multiplier
- US and Indian yarn specifications
- GATE textile yarn manufacture problems
Convert turns per inch to other units
| Conversion | 1 TPI equals | Reverse |
|---|---|---|
| turn per inch to turn per metre | 39.37007874 TPM | turn per metre to turn per inch |
| turn per inch to turn per centimetre | 0.3937007874 TPcm | turn per centimetre to turn per inch |
| turn per inch to turn per foot | 12 TPF | turn per foot to turn per inch |
Open the Yarn Twist Converter to convert any value between all units.
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".
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). Turn per Inch (TPI). Retrieved October 25, 2026, from https://scientificconverters.com/units/turn-per-inch/
IEEE
Scientific Converters, "Turn per Inch (TPI)," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/units/turn-per-inch/