# Thread Pitch Calculator

URL: https://speedycalculator.com/calculators/construction/thread-pitch/
Last updated: 2026-10-25

> The thread pitch calculator finds the pitch of a screw thread from the number of threads counted over a measured length, in millimetres and threads per inch (TPI), and converts between the two.

## Inputs

- Measured length (mm, in)
- Number of threads counted

## Results

- Thread pitch
- Threads per inch (TPI)

## Formula

```
Pitch P = length ÷ number of threads
TPI = threads ÷ length in inches = 25.4 ÷ P (mm)
```

## Explanation

If you do not have a thread gauge, count the thread crests over a known length with a ruler or caliper. Metric threads are specified by pitch in millimetres; unified (inch) threads by threads per inch. Counting over a longer length gives a more accurate result.

### How to use the Thread Pitch Calculator

- **Measured length**
- **Number of threads counted**
- Every result field is editable: type into **Thread pitch** and **Number of threads counted** plus every other field update to match.

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the measured length and the number of complete threads in it. Type a pitch into the result to find how many threads fit in the length.

### Tips for an accurate estimate

- Keep units consistent – the calculator handles conversions, but check every field's unit before reading a result.
- Use values from standards, data sheets or test pieces whenever you have them; typical values are only a starting point.
- Apply appropriate safety factors and have structural, electrical and pressure work checked by a qualified professional.
- Record the inputs you used so the calculation can be reviewed later.

### Common mistakes to avoid

- Confusing diameter and radius, or nominal and actual sizes.
- Using allowable stresses and ultimate strengths interchangeably.
- Treating rule-of-thumb results as a substitute for code tables or an engineered design.

### Inputs explained

FieldWhat to enterMeasured lengthUnits: mm, inNumber of threads countedA number

### What each result means

- **Thread pitch** = [Measured length]÷[Number of threads counted]
- **Threads per inch (TPI)** = 0.0254÷[Thread pitch]

### Example values

How the main result changes when **Number of threads counted** changes and everything else stays at the example values above:

Number of threads countedThread pitch (mm)537.52101.512.51.2151200.75

## Worked example

Inputs — Measured length: 15 mm; Number of threads counted: 10.

Results — **Thread pitch = 1.5 mm**; Threads per inch (TPI) = 16.93.

## FAQ

**How do I convert TPI to pitch?**
Pitch (mm) = 25.4 ÷ TPI. 20 TPI = 1.27 mm.

**Is ¼-20 the same as M6 × 1?**
No – ¼ in is 6.35 mm and 20 TPI is 1.27 mm pitch; they are not interchangeable.

**How accurate is counting threads?**
Counting 10 or more threads over a measured length usually identifies the standard pitch exactly.

**What formula does the Thread Pitch Calculator use?**
Pitch P = length ÷ number of threads.