Inches to millimeters is the critical conversion for anyone working across imperial and metric precision tooling. CNC machinists, 3D printer operators, mechanical engineers, and anyone specifying hardware tolerances need millimeter accuracy. Unlike centimeters, millimeters avoid decimal points for most practical measurements, making them the default unit on engineering drawings worldwide.
How to Calculate Inches to Millimeters (Step by Step)
Step One: Multiply inches by 25.4
The exact conversion factor is 25.4 millimeters per inch, defined internationally since 1959.
Millimeters = Inches x 25.4
Step Two: Worked example with default value (6 inches)
Millimeters = 6 x 25.4 = 152.400 mm
Six inches converts to exactly 152.4 millimeters with no rounding needed.
Step Three: Verify with centimeters (optional cross-check)
Since 1 cm = 10 mm, you can divide your mm result by 10 to confirm against a cm conversion.
Centimeters = 6 x 2.54 = 15.240 cm
Check: 152.4 mm / 10 = 15.24 cm (confirmed)
What Your Results Mean
The Millimeters result is your primary output, formatted to three decimal places for precision work. The Centimeters result is provided for reference when you need the same measurement for less precision-critical applications.
Precision considerations
In machining, tolerances are often +/-0.05 mm or tighter. When converting imperial drawings to metric for CNC work, always carry at least three decimal places. A 0.250-inch shaft is 6.350 mm, not “about 6.4 mm,” and that 0.05 mm difference matters for press fits and bearing journals.
Common inches-to-mm reference conversions
- 1/32 inch to mm = 0.79375 mm
- 1/16 inch to mm = 1.5875 mm
- 3/32 inch to mm = 2.38125 mm
- 1/8 inch to mm = 3.175 mm
- 5/32 inch to mm = 3.96875 mm
- 3/16 inch to mm = 4.7625 mm
- 7/32 inch to mm = 5.55625 mm
- 1/4 inch to mm = 6.35 mm
- 9/32 inch to mm = 7.14375 mm
- 5/16 inch to mm = 7.9375 mm
- 11/32 inch to mm = 8.73125 mm
- 3/8 inch to mm = 9.525 mm
- 13/32 inch to mm = 10.31875 mm
- 7/16 inch to mm = 11.1125 mm
- 15/32 inch to mm = 11.90625 mm
- 1/2 inch to mm = 12.7 mm
- 9/16 inch to mm = 14.2875 mm
- 5/8 inch to mm = 15.875 mm
- 11/16 inch to mm = 17.4625 mm
- 3/4 inch to mm = 19.05 mm
- 13/16 inch to mm = 20.6375 mm
- 7/8 inch to mm = 22.225 mm
- 15/16 inch to mm = 23.8125 mm
- 1 inch to mm = 25.4 mm
- 2 inches to mm = 50.8 mm
- 3 inches to mm = 76.2 mm
- 4 inches to mm = 101.6 mm
- 5 inches to mm = 127 mm
- 6 inches to mm = 152.4 mm
- 7 inches to mm = 177.8 mm
- 8 inches to mm = 203.2 mm
- 9 inches to mm = 228.6 mm
- 10 inches to mm = 254 mm
- 11 inches to mm = 279.4 mm
- 12 inches to mm = 304.8 mm
- 18 inches to mm = 457.2 mm
- 24 inches to mm = 609.6 mm
- 36 inches to mm = 914.4 mm
- 48 inches to mm = 1219.2 mm
- 60 inches to mm = 1524 mm
- 72 inches to mm = 1828.8 mm
- 84 inches to mm = 2133.6 mm
- 96 inches to mm = 2438.4 mm
For working with fractional inch measurements (like 5/16” or 7/32”), convert to decimal first with the inches fraction to decimal calculator, then run the result through this converter. If you’re converting larger measurements where meters are more appropriate, try the inches to meters converter. For the reverse direction, the mm to inches calculator converts metric measurements back to imperial.