conversions
Inches to Millimeters
Last updated: May 31, 2026
Written by Blake Boege
An inches to millimeters converter is a linear measurement utility that translates lengths between the imperial system (inches) and the metric system (millimeters). It applies the standard conversion factor where one inch is defined as exactly 25.4 millimeters. It is widely used in engineering, machining, woodworking, and international product manufacturing.
Convert inches to millimeters instantly. Read the conversion answers, the mathematical formula, and browse the reference lookup table.
Quick Answer
Convert inches to millimeters instantly. 1 inch is equal to exactly 25.4 millimeters.
Inches to Millimeters
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Answer
25.4 mm
1 in = 25.4 mm
Inches to Millimeters Reference Table
| Inches (in) | Millimeters (mm) | Description |
|---|---|---|
| 1 in | 25.40 mm | Exactly one inch (postage stamp width) |
| 5 in | 127.00 mm | Standard index card length |
| 10 in | 254.00 mm | Average iPad screen height |
| 25 in | 635.00 mm | Average electric guitar neck length |
| 50 in | 1,270.00 mm | Width of a 55-inch flat screen TV |
| 100 in | 2,540.00 mm | Height of a standard residential doorway |
Examples
1 in
25.4 mm
How it works
To convert inches (in) to millimeters (mm), perform the following calculation:
Formula
mm = in × 25.4
Method
Multiply inches by 25.4 to get millimeters.
Understanding Inches to Millimeters Conversions
Converting measurements between metric and imperial scales, or relative speed and capacity benchmarks, is essential in sciences, logistics, cooking, and daily travel. Using standard multipliers guarantees precision and alignment across different measurement systems.
How to convert inches to millimeters
To perform the conversion manually, use the formula mm = in × 25.4. For example, to convert 10 inches into millimeters, multiply 10 by 25.4, yielding 254 mm.
How to convert millimeters to inches
To reverse the conversion, use the formula in = mm ÷ 25.4. For instance, if you have 100 millimeters, divide 100 by 25.4 (or multiply by its reciprocal 0.03937008), which equals 3.9370 in.
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Frequently asked questions
Multiply the inch value by 25.4. For example, 2 inches = 2 × 25.4 = 50.8 mm.
There are exactly 25.4 millimeters in 1 inch.
In 1959, the international yard and pound agreement standardized the inch as exactly 25.4 millimeters, establishing a clean bridge between metric and imperial systems.
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