ISO metric threads have a 60° profile and are designated by diameter and pitch, such as 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
| Size | Pitch (mm) | Tap drill (mm) | Stress area (mm²) |
|---|---|---|---|
| M3 | 0.5 | 2.5 | 5.0 |
| M4 | 0.7 | 3.3 | 8.8 |
| M5 | 0.8 | 4.2 | 14.2 |
| M6 | 1 | 5 | 20.1 |
| M8 | 1.25 | 6.75 | 36.6 |
| M10 | 1.5 | 8.5 | 58.0 |
| M12 | 1.75 | 10.25 | 84.3 |
| M16 | 2 | 14 | 156.7 |
| M20 | 2.5 | 17.5 | 244.8 |
| M24 | 3 | 21 | 352.5 |
| M30 | 3.5 | 26.5 | 560.6 |
| M36 | 4 | 32 | 816.7 |
Inputs explained
| Field | What to enter |
|---|---|
| Nominal (major) diameter | Units: mm, in, cm |
| Pitch | Units: 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
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
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.
Frequently asked questions
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.