inch ↔ mm Converter

Convert between inches and millimeters instantly.

A precise, user-friendly unit converter built specifically for engineers, machinists, makers, and students who work across metric and imperial systems. Easily convert between inches and millimeters with up to 6 decimal places of precision. Supports fractional input like 1/8, 1 1/4, and displays exact simplified fractional equivalents (e.g., 1 3/8") when applicable. Developed by a mechanical engineer using ChatGPT as a collaborative coding assistant — combining real-world engineering needs with fast, intelligent development.