Convert metric thread pitch in millimeters to threads per inch (TPI), or convert TPI to metric pitch. Compare common thread standards and find close pitch equivalents.
| Metric pitch | TPI equivalent | Threads / inch |
|---|---|---|
| 0.40 mm | 63.500 TPI | 63.50 |
| 0.45 mm | 56.444 TPI | 56.44 |
| 0.50 mm | 50.800 TPI | 50.80 |
| 0.60 mm | 42.333 TPI | 42.33 |
| 0.70 mm | 36.286 TPI | 36.29 |
| 0.75 mm | 33.867 TPI | 33.87 |
| 0.80 mm | 31.750 TPI | 31.75 |
| 1.00 mm | 25.400 TPI | 25.40 |
| 1.25 mm | 20.320 TPI | 20.32 |
| 1.50 mm | 16.933 TPI | 16.93 |
| 1.75 mm | 14.514 TPI | 14.51 |
| 2.00 mm | 12.700 TPI | 12.70 |
| 2.50 mm | 10.160 TPI | 10.16 |
| 3.00 mm | 8.467 TPI | 8.47 |
| 3.50 mm | 7.257 TPI | 7.26 |
| 4.00 mm | 6.350 TPI | 6.35 |
| 4.50 mm | 5.644 TPI | 5.64 |
| 5.00 mm | 5.080 TPI | 5.08 |
| Thread | Standard | TPI | Pitch mm |
|---|---|---|---|
| 1/4-20 | UNC | 20 | 1.2700 |
| 1/4-28 | UNF | 28 | 0.9071 |
| 5/16-18 | UNC | 18 | 1.4111 |
| 5/16-24 | UNF | 24 | 1.0583 |
| 3/8-16 | UNC | 16 | 1.5875 |
| 3/8-24 | UNF | 24 | 1.0583 |
| 7/16-14 | UNC | 14 | 1.8143 |
| 7/16-20 | UNF | 20 | 1.2700 |
| 1/2-13 | UNC | 13 | 1.9538 |
| 1/2-20 | UNF | 20 | 1.2700 |
| 9/16-12 | UNC | 12 | 2.1167 |
| 9/16-18 | UNF | 18 | 1.4111 |
| 5/8-11 | UNC | 11 | 2.3091 |
| 5/8-18 | UNF | 18 | 1.4111 |
| 3/4-10 | UNC | 10 | 2.5400 |
| 3/4-16 | UNF | 16 | 1.5875 |
| 7/8-9 | UNC | 9 | 2.8222 |
| 7/8-14 | UNF | 14 | 1.8143 |
| 1-8 | UNC | 8 | 3.1750 |
| 1-12 | UNF | 12 | 2.1167 |
How do I convert mm pitch to TPI? Divide 25.4 by the pitch in millimeters. For example, 1.5 mm gives 16.933 TPI.
How do I convert TPI to metric pitch? Divide 25.4 by the TPI value. For example, 20 TPI equals 1.27 mm pitch.
What does TPI stand for? TPI means threads per inch and describes the number of thread pitches across one inch.
What is a metric thread pitch? It is the axial distance between corresponding points on neighboring threads, expressed in millimeters.
Is 1.25 mm the same as 20 TPI? No. 1.25 mm equals 20.32 TPI. It is close in spacing to 20 TPI but is not identical.
Can I use a metric bolt with an imperial nut if the pitch is close? No. Close pitch alone is not sufficient. The diameter, profile, angle, tolerance and standard must match for proper mechanical compatibility.
Does higher TPI mean a finer thread? For the same nominal diameter, a higher TPI means smaller distance between threads and therefore a finer thread.
Does this identify the complete thread standard? No. Pitch conversion identifies spacing only. Complete identification also requires diameter and the applicable thread standard and tolerance.