# Thread Calculator

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

> The thread calculator gives the basic dimensions of ISO metric screw threads – major, pitch and minor diameters, thread depth, tap drill size and tensile stress area – for any diameter and pitch.

## Inputs

- Nominal (major) diameter (mm, in, cm)
- Pitch (mm, in)

## Results

- Fundamental triangle height H
- Pitch diameter
- Minor diameter (external)
- Minor diameter (internal)
- Thread depth (external)
- Tap drill
- Tensile stress area

## Formula

```
H = 0.866025 P; d₂ = d − 0.649519 P
d₃ = d − 1.226869 P (external minor); D₁ = d − 1.082532 P (internal minor)
Thread depth h₃ = 0.613343 P; tap drill ≈ d − P
Stress area Aₛ = π/4 × (d − 0.938194 P)²
```

## Explanation

ISO metric threads have a 60° profile and are designated by diameter and pitch – M10 × 1.5. Coarse pitches are the default; fine pitches are used for adjustment and thin walls. The tensile stress area is used to calculate bolt strength, and the tap drill size gives about 75% thread engagement.

### How to use the Thread Calculator

- **Nominal (major) diameter**
- **Pitch**

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

### How it works

Enter the nominal diameter and the pitch (see the coarse pitch table below).

### ISO coarse pitches

SizePitch (mm)Tap drill (mm)Stress area (mm²)M30.52.55.0M40.73.38.8M50.84.214.2M61520.1M81.256.7536.6M101.58.558.0M121.7510.2584.3M16214156.7M202.517.5244.8M24321352.5M303.526.5560.6M36432816.7

### 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 enterNominal (major) diameterUnits: mm, in, cmPitchUnits: mm, in

### What each result means

- **Fundamental triangle height H** = 0.866025×[Pitch]
- **Pitch diameter** = [Nominal (major) diameter] - 0.649519×[Pitch]
- **Minor diameter (external)** = [Nominal (major) diameter] - 1.226869×[Pitch]
- **Minor diameter (internal)** = [Nominal (major) diameter] - 1.082532×[Pitch]
- **Thread depth (external)** = 0.613343×[Pitch]
- **Tap drill** = [Nominal (major) diameter] - [Pitch]
- **Tensile stress area** = pi÷4×([Nominal (major) diameter] - 0.938194×[Pitch])^2

## Worked example

Inputs — Nominal (major) diameter: 10 mm; Pitch: 1.5 mm.

Results — Fundamental triangle height H = 1.299 mm; Pitch diameter = 9.0257 mm; Minor diameter (external) = 8.1597 mm; Minor diameter (internal) = 8.3762 mm; Thread depth (external) = 0.92 mm; **Tap drill = 8.5 mm**; Tensile stress area = 57.99 mm².

## FAQ

**What is the tap drill for M10 × 1.5?**
8.5 mm (10 − 1.5).

**What is the stress area of an M12 bolt?**
84.3 mm² for M12 × 1.75.

**What pitch is M8?**
1.25 mm coarse; 1.0 mm fine.

**What formula does the Thread Calculator use?**
H = 0.866025 P; d₂ = d − 0.649519 P.


## Sources

- [ISO 724 / ISO 898-1 – Metric screw threads and stress area](https://www.iso.org/)