Convert Turns per Foot to Turns per Inch (TPF to TPI)
1 turn per foot (TPF) = 0.08333333333 turns per inch (TPI). 1 TPI = 12 TPF. Example: 15 TPF = 15 × 0.08333333333 = 1.25 TPI.
Also searched as turns per foot to TPI, turns per foot in TPI, turns per foot into turns per inch, TPF to TPI, TPF in turns per inch, TPF into turn per inch, turn per foot to turn per inch, TPF to turns per inch converter and how many turns per inch in a turn per foot.
1 TPF = 0.08333333333 TPI
Type in either box. Scientific notation works: 1.5e-3.
Converting a list? Use the bulk turn per foot to turn per inch converter to paste a column from Excel.
How to Convert Turn per Foot to Turn per Inch
- 1 TPF = 0.08333333333 TPI
- 1 TPI = 12 TPF
- Example: convert 15 TPF to TPI: 15 TPF = 15 × 0.08333333333 TPI = 1.25 TPI
Formula
TPI = TPF ÷ 12
Derivation from SI units:
- 1 turn per foot = 1 turn per 0.3048 m = 3.280839895 TPM (exact)
- 1 TPI = 1 turn per 0.0254 m = 39.37007874 TPM (exact)
- 1 TPF = 3.280839895013 TPM ÷ 39.37007874016 TPM per TPI = 0.08333333333333 TPI
Both units are defined exactly, so the factor is exact. Turn per Foot definition: turn per foot; Turn per Inch definition: turn per inch.
Worked examples
- A reading of 5 TPF converts to 0.4166666667 TPI.
5 TPF × 0.08333333333 = 0.4166666667 TPI - A value of 12 TPF is 1 TPI.
12 TPF × 0.08333333333 = 1 TPI
Turn per Foot to Turn per Inch conversion table
| Turns per Foot (TPF) | Turns per Inch (TPI) |
|---|---|
| 1 TPF | 0.08333333333 TPI |
| 2 TPF | 0.1666666667 TPI |
| 3 TPF | 0.25 TPI |
| 5 TPF | 0.4166666667 TPI |
| 8 TPF | 0.6666666667 TPI |
| 10 TPF | 0.8333333333 TPI |
| 12 TPF | 1 TPI |
| 20 TPF | 1.666666667 TPI |
| 30 TPF | 2.5 TPI |
| 50 TPF | 4.166666667 TPI |
Where it's used
Turns per Foot are used for cords, ropes and tyre cords, while turns per inch appear in cotton-system spinning (ring, rotor) and twist multiplier. Both measure yarn twist (turns per unit length), so the conversion is a fixed factor.
Turn per Foot to other yarn twist units
| Conversion | 1 TPF equals |
|---|---|
| turn per foot to turn per inch | 0.08333333333 TPI |
| turn per foot to turn per metre | 3.280839895 TPM |
| turn per foot to turn per centimetre | 0.03280839895 TPcm |
Frequently asked questions
How many turns per inch are in 1 turn per foot?
1 TPF = 0.08333333333 TPI.
How do I convert turns per foot to turns per inch?
Multiply the value in TPF by 0.08333333333, or divide it by 12. For example, 15 TPF × 0.08333333333 = 1.25 TPI.
Is the TPF to TPI 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, "foot".
- 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). Convert Turns per Foot to Turns per Inch (TPF to TPI). Retrieved October 25, 2026, from https://scientificconverters.com/yarn-twist/turns-per-foot-to-turns-per-inch/
IEEE
Scientific Converters, "Convert Turns per Foot to Turns per Inch (TPF to TPI)," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/yarn-twist/turns-per-foot-to-turns-per-inch/