mm to Inches: Formula, Chart and Common Sizes

One inch is defined as exactly 25.4 millimetres, so every conversion here is exact rather than approximate.

The formula inches = millimetres ÷ 25.4 millimetres = inches × 25.4

Chart 1 mm = 0.0394 in. 5 mm = 0.197 in. 10 mm = 0.394 in. 25 mm = 0.984 in. 50 mm = 1.969 in. 100 mm = 3.937 in. 300 mm = 11.811 in.

Fractional inches Hardware still uses fractions. 1/16 in = 1.588 mm. 1/8 in = 3.175 mm. 1/4 in = 6.35 mm. 1/2 in = 12.7 mm. 3/4 in = 19.05 mm.

Where it matters Timber sold as a "2×4" is nominally 2×4 inches but actually 38 × 89 mm after planing. Screen sizes are diagonal inches: a 15.6-inch laptop panel measures 396 mm corner to corner. A4 paper is 210 × 297 mm, which is 8.27 × 11.69 inches — never quite the same as US Letter at 216 × 279 mm.