How to Convert Inches to Millimeters
Converting inches to millimeters multiplies by 25.4 exactly — this is an internationally defined relationship (1 inch = 25.4 mm since 1959). One of the most precise and widely used conversions in engineering and manufacturing.
1.00 Inches = 25.4000 Millimeters
Multiply by 25.4 to get your result.
Step-by-Step
- Start with your value: 1.00 inches
- Multiply by 25.4
- Result: 25.4000 millimeters
Formula: Millimeters = Inches × 25.4
💡 Memory Tip: 1 inch = exactly 25.4 mm. This is one of the few exact, defined conversions. Multiply by 25.4.
Inches to Millimeters Quick Reference
| Inches | Millimeters | Reference |
|---|---|---|
| 1 | 25.4 | 1 inch exactly |
| 0.5 | 12.7 | Half inch |
| 12 | 304.8 | 1 foot |
| 6 | 152.4 | 6 inches |
| 36 | 914.4 | 1 yard |
What does 1 inches look like in real life?
Real-world objects and measurements that are approximately 1 inch (25.40 millimeters) — useful for visualizing the size of 1 inch without a ruler:
- a paper clip length (~1 in)
- a US quarter diameter (0.96 in)
Understanding Inches and Millimeters
What is an Inch?
The inch is a unit of length in the imperial and US customary systems, defined as exactly 25.4 millimeters since the international yard and pound agreement of July 1, 1959.
Learn more about inches on Wikipedia →
What is a Millimeter?
The millimeter is a unit of length in the metric system, equal to one thousandth of a meter (0.001 m). It is the standard unit for precision measurements in engineering, manufacturing, and medicine.
Learn more about millimeters on Wikipedia →
Common Uses of Inches
TV and monitor screen sizes (diagonal), Smartphone and tablet screen sizes, Body height (in the US), Paper dimensions (US Letter, US Legal).
Key Conversion Facts
- 1 inch = exactly 2.54 cm (defined 1959)
- 12 inches = 1 foot
- 36 inches = 1 yard
- 5,280 feet = 1 mile
- Used in the US for body height, screen sizes, paper dimensions, and rainfall
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Frequently Asked Questions
1 inches equals 25.4000 millimeters.
Millimeters = Inches × 25.4
For 1 inches: 1 gives 25.4000 millimeters.
1 inches = 2.5400 cm.
1 inches = 25.4000 millimeters. This is a standard measurement used in many practical applications including construction, science, and everyday life.
In 1959, English-speaking nations (US, UK, Canada, Australia) redefined the yard as exactly 0.9144 meters, making 1 inch = 0.0254 m = 25.4 mm. This international yard eliminated small discrepancies between national standards.
