Inches to MM Converter
Convert inches to millimetres quickly. Free online inch to mm calculator with common conversions and formula.
Formula
mm = inches × 25.4
Common Conversions
How to Convert Inches to Millimetres
1 inch = 25.4 mm exactly. Multiply inches by 25.4 to get millimetres. So 4 in × 25.4 = 101.6 mm. The exact factor of 25.4 makes this a precise conversion - useful for engineering work where dimensional accuracy matters.
Common DIY application: converting US lumber sizes to mm. A '2x4' US lumber actually measures 38 mm × 89 mm finished (the nominal '2x4' is rough-sawn dimension before planing). Similarly, screw sizes: 1/4 inch = 6.35 mm, 1/2 inch = 12.7 mm, 1 inch = 25.4 mm.
Common Inches to Millimetres Conversions
| Inches | Millimetres |
|---|---|
| 1/8 in | 3.18 mm |
| 1/4 in | 6.35 mm |
| 1/2 in | 12.7 mm |
| 3/4 in | 19.05 mm |
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 6 in | 152.4 mm |
| 12 in (1 ft) | 304.8 mm |
Frequently Asked Questions
What are common fractional inch conversions?
1/16 in = 1.59 mm, 1/8 in = 3.18 mm, 1/4 in = 6.35 mm, 1/2 in = 12.7 mm, 3/4 in = 19.05 mm, 1 in = 25.4 mm. These show up in lumber, fasteners, and pipe sizes.
Is 1 inch always 25.4 mm?
Yes, by international agreement since 1959. Before that, the US and UK had slightly different inches (the difference was tiny - about 1/100,000th). The 1959 agreement standardised exact conversion factors for all imperial-to-metric units.
Related Tools
MM to Inches Converter
Convert millimetres to inches instantly. Free online mm to inch calculator with common conversion table and formula.
Cm to Inches Converter
Instantly convert centimetres to inches with our free, lightning-fast calculator. Perfect for DIY, tailoring, and converting UK to US measurements.
Feet to Metres Converter
Convert feet to metres with our free converter. Quick reference table of common feet to metre conversions.