Convert Turns per Inch to Turns per Foot (TPI to TPF)
1 turn per inch (TPI) = 12 turns per foot (TPF). 1 TPF = 0.08333333333 TPI. Example: 15 TPI = 15 × 12 = 180 TPF.
Also searched as turns per inch to TPF, turns per inch in TPF, turns per inch into turns per foot, TPI to TPF, TPI in turns per foot, TPI into turn per foot, turn per inch to turn per foot, TPI to turns per foot converter and how many turns per foot in a turn per inch.
1 TPI = 12 TPF
Type in either box. Scientific notation works: 1.5e-3.
Converting a list? Use the bulk turn per inch to turn per foot converter to paste a column from Excel.
How to Convert Turn per Inch to Turn per Foot
- 1 TPI = 12 TPF
- 1 TPF = 0.08333333333 TPI
- Example: convert 15 TPI to TPF: 15 TPI = 15 × 12 TPF = 180 TPF
Formula
TPF = TPI × 12
Derivation from SI units:
- 1 TPI = 1 turn per 0.0254 m = 39.37007874 TPM (exact)
- 1 turn per foot = 1 turn per 0.3048 m = 3.280839895 TPM (exact)
- 1 TPI = 39.37007874016 TPM ÷ 3.280839895013 TPM per TPF = 12 TPF
Both units are defined exactly, so the factor is exact. Turn per Inch definition: turn per inch; Turn per Foot definition: turn per foot.
Worked examples
- A reading of 10 TPI converts to 120 TPF.
10 TPI × 12 = 120 TPF - A value of 16.1 TPI is 193.2 TPF.
16.1 TPI × 12 = 193.2 TPF
Turn per Inch to Turn per Foot conversion table
| Turns per Inch (TPI) | Turns per Foot (TPF) |
|---|---|
| 3 TPI | 36 TPF |
| 5 TPI | 60 TPF |
| 8 TPI | 96 TPF |
| 10 TPI | 120 TPF |
| 12 TPI | 144 TPF |
| 15 TPI | 180 TPF |
| 16.1 TPI | 193.2 TPF |
| 18 TPI | 216 TPF |
| 20 TPI | 240 TPF |
| 25 TPI | 300 TPF |
Where it's used
Turns per Inch are used for cotton-system spinning (ring, rotor) and twist multiplier, while turns per foot appear in cords, ropes and tyre cords. Both measure yarn twist (turns per unit length), so the conversion is a fixed factor.
Turn per Inch to other yarn twist units
| Conversion | 1 TPI equals |
|---|---|
| turn per inch to turn per foot | 12 TPF |
| turn per inch to turn per metre | 39.37007874 TPM |
| turn per inch to turn per centimetre | 0.3937007874 TPcm |
Frequently asked questions
How many turns per foot are in 1 turn per inch?
1 TPI = 12 TPF.
How do I convert turns per inch to turns per foot?
Multiply the value in TPI by 12. For example, 15 TPI × 12 = 180 TPF.
Is the TPI to TPF conversion exact?
Yes. Both units are defined exactly, and 1 TPI is exactly 12 TPF.
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".
- 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, "foot".
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 Foot (TPI to TPF). Retrieved October 25, 2026, from https://scientificconverters.com/yarn-twist/turns-per-inch-to-turns-per-foot/
IEEE
Scientific Converters, "Convert Turns per Inch to Turns per Foot (TPI to TPF)," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/yarn-twist/turns-per-inch-to-turns-per-foot/