How Many Millimeters in an Inch
Instant inch to millimeter conversion
⚡Quick Answer
1 inch = 25.4 millimeters (exactly). To convert inches to mm, multiply by 25.4.
in
=25.4mm
Step-by-Step Guide
1
The Exact Conversion
1 inch = 25.4 millimeters. This is an internationally agreed exact definition since 1959.
💡This is not a rounded number—it's the exact definition.
2
Conversion Formula
To convert inches to millimeters: mm = inches × 25.4. Example: 3 inches = 3 × 25.4 = 76.2 mm.
💡For quick mental math, multiply by 25 and add a bit more.
3
Common Conversions
1/4 inch = 6.35 mm | 1/2 inch = 12.7 mm | 1 inch = 25.4 mm | 2 inches = 50.8 mm
💡These are common sizes for screws, bolts, and hardware.
4
MM to Inches
To convert mm to inches: inches = mm ÷ 25.4. Example: 50 mm = 50 ÷ 25.4 = 1.97 inches.
💡Or multiply mm by 0.03937 for the same result.
Frequently Asked Questions
Why do we need to convert between inches and mm?
The US uses inches while most of the world uses metric (mm). This matters for tools, hardware, engineering, and 3D printing.
What's the difference between mm and cm?
1 centimeter = 10 millimeters. So 1 inch = 25.4 mm = 2.54 cm.
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