1 Inch (in) to Millimetre (mm)
1 in = 25.4 mm
1 Inch equals 25.4 Millimetre — that is, 1 in = 25.4 mm. You get there by multiplying the value in Inch by 25.4, the conversion factor between these two Length units. The table below covers the other most-searched values, and the converter accepts any number.
Formula
mm = in × 25.4in to mm conversion table
Frequently asked questions
How many mm are in 1 in?+
1 Inch equals 25.4 Millimetre, so 1 in = 25.4 mm.
What is the formula to convert in to mm?+
Multiply the number of Inch by 25.4. In other words: mm = in × 25.4.
How much is 1 in in mm?+
1 Inch = 25.4 Millimetre (1 in = 25.4 mm).
Is this conversion exact?+
Yes. The factor used is the unit’s official definition; results are rounded to 10 significant digits for readability.