Thread Calculator

Thread Calculator works out the full geometry of a standard 60° screw thread — Unified inch or ISO metric — from just the major diameter and the pitch. Enter a size and read the pitch, major and minor diameters, the thread height, the tap drill for the percentage of thread you want, the recommended engagement length and the class-of-fit limits straight away. It works completely offline and nothing you enter ever leaves your phone.

HOW IT WORKS
The app uses the 60° thread form shared by ASME B1.1 (Unified) and ISO 68-1 / ISO 965 (metric):

1. The sharp V of the thread has a height H = (square root of 3, divided by 2) times the pitch P, about 0.866 times P.

2. The tip and valley of that V are flattened — the crest by H/8 and the root by H/4 — leaving five eighths of H as the working flank.

3. The pitch diameter is d2 = d minus 0.6495 times P, the basic minor diameter is d minus 1.0825 times P, and the external design minor and thread heights follow from the same triangle.

4. The tap drill for a tapped hole is the internal minor diameter for the percentage of thread you choose: hole = major minus (percent / 100) times 1.299 times P. Seventy-five percent is the usual target, close to the familiar "diameter minus pitch" rule.

For M12 x 1.75 the pitch diameter is 10.863 mm, the 75 percent tap drill is 10.3 mm and the tensile stress area is 84.3 square millimetres — matching the standard tables.

WHAT YOU CAN DO
- Switch between metric (mm and pitch) and Unified inch (inch and threads per inch)
- Read the pitch, major and minor diameters, thread height H and the fundamental truncations
- Get the tap drill for any thread percentage from 50 to 100, with the nearest number, letter, fractional or metric drill
- See the recommended thread engagement length in steel, cast iron or aluminium
- Check the 6g / 6H (2A / 2B) allowances and pitch-diameter max and min
- Open Details for a full step-by-step breakdown and a reference chart of common threads
- Learn the 60° form, the three diameters and tap drilling in plain language

BUILT FOR CLARITY
A clean, machined-metal design puts the pitch diameter first, with the supporting dimensions right beside it. Light and dark themes, a tiny download, no clutter and no account required.

AN ESTIMATE, NOT A GAUGING PROCEDURE
This app gives reference geometry for standard 60° threads, not an inspection or gauging procedure. Whether a manufactured thread is acceptable is decided by thread ring and plug gauges and the governing standard — ASME B1.1 or ISO 965 — not by these nominal figures. Confirm critical fasteners and thread fits against the specification, and where safety depends on it, a qualified engineer. This app is for general information and education only and is not professional engineering advice.

PRIVACY
The app collects no personal data and works fully offline. Ads are served by Google AdMob, which may use an advertising identifier as described in Google's policies.

Download Thread Calculator and keep the complete thread dimension set for any bolt or tapped hole in your pocket.