The conversion
One inch is exactly 25.4 millimetres. To convert millimetres to inches divide by 25.4, and to convert inches to millimetres multiply by 25.4.
Common luthier measurements
| Inches | Millimetres |
|---|---|
| 25.5" scale | 647.7 mm |
| 24.75" scale | 628.65 mm |
| 650 mm scale | 25.591" |
| 34" bass scale | 863.6 mm |
| 1 11/16" nut width | 42.86 mm |
| 1/8" | 3.175 mm |
| 1/16" | 1.5875 mm |
| 1/32" | 0.794 mm |
| 1/64" | 0.397 mm |
About the fractions
Fractions are rounded to the nearest 1/64", so they are close approximations rather than exact values. The decimal figure is the precise one.
Frequently asked questions
How many millimetres are in an inch?
Exactly 25.4 millimetres.
How do I convert a fraction of an inch to mm?
Convert the fraction to a decimal, then multiply by 25.4. For example 1/8" is 0.125 × 25.4 = 3.175 mm.