Inches to Millimeters Converter
Convert inches to millimeters accurately. Great for technical measurements.
Common Conversions
Related Calculators
What is Inches to Millimeters Converter?
The inches to millimeters converter converts imperial inch measurements to the metric millimeter. One inch equals exactly 25.4 millimeters, a relationship that is exact and defined, not approximated. This conversion is fundamental in manufacturing, engineering, hardware, and precision work where imperial and metric specifications must be reconciled.
Millimeters are the precision standard in metric manufacturing: CNC machining tolerances, electronic component dimensions, bearing sizes, and fastener diameters are all specified in millimeters. American manufacturers and engineers frequently need to convert their inch-based designs to millimeters for international manufacturing, and vice versa. The inches-to-mm conversion is one of the most common tasks in global product design and quality control.
How to Use This Calculator
Enter the value in inches (decimal or fraction converted to decimal) and the converter instantly displays the equivalent in millimeters. Formula: mm = inches × 25.4. For fractional inches, divide the numerator by the denominator first. For example, 3/8 inch = 0.375, then 0.375 × 25.4 = 9.525 mm.
Worked Examples
CNC Machining Tolerance
A design specifies a tolerance of ±0.005 inches. Converting: 0.005 × 25.4 = ±0.127 mm. For a hole diameter of 0.750 inches: 0.750 × 25.4 = 19.05 mm. Metric CNC programs need all dimensions in millimeters, making this conversion essential for international manufacturing.
Pipe Sizes
A 1/2-inch pipe fitting: 0.5 × 25.4 = 12.7 mm nominal diameter. A 3/4-inch pipe: 0.75 × 25.4 = 19.05 mm. Note that pipe sizes are nominal, not actual outside diameters, but the conversion factor remains the same for comparing specifications across systems.
Woodworking: Dado Blade Width
Setting a dado blade stack to 3/4 inch width: 0.75 × 25.4 = 19.05 mm. When using a metric router with mm adjustment, this conversion ensures the groove matches the standard 3/4-inch plywood thickness used in US cabinetry.
Inches to Millimeters Conversion Table
| Inches | Millimeters |
|---|---|
| 0.25 in (1/4") | 6.350 mm |
| 0.5 in (1/2") | 12.700 mm |
| 1 in | 25.400 mm |
| 2 in | 50.800 mm |
| 3 in | 76.200 mm |
| 4 in | 101.600 mm |
| 5 in | 127.000 mm |
| 6 in | 152.400 mm |
| 7 in | 177.800 mm |
| 8 in | 203.200 mm |
| 9 in | 228.600 mm |
| 10 in | 254.000 mm |
| 11 in | 279.400 mm |
| 12 in | 304.800 mm |
Benefits of Using This Calculator
- Convert imperial fastener and hardware dimensions to metric for international sourcing
- Translate inch-based design specifications to mm for metric manufacturing
- Determine drill bit and tooling sizes in millimeters from fractional inch specifications
- Specify tolerances in metric documentation when working from US drawings
- Convert pipe and tube sizes between inch and mm standards
- Essential for 3D printing, CNC machining, and precision manufacturing
Practical Tips
- The key: 1 inch = 25.4 mm exactly. Multiply inches by 25.4 for the exact mm value.
- Common fractions: 1/4" = 6.35 mm, 1/2" = 12.7 mm, 3/4" = 19.05 mm, 1" = 25.4 mm.
- For precision work, avoid rounding intermediate results — use the full 25.4 mm per inch factor.
- Metric and imperial fasteners are specified differently even when close in size; never assume interchangeability.
Key Takeaways
- 11 inch = exactly 25.4 mm — this is the foundational metric-imperial length conversion.
- 2Multiply inches by 25.4 to get millimeters.
- 3Common fractions: 1/4" = 6.35 mm; 1/2" = 12.7 mm; 3/4" = 19.05 mm.
- 4This conversion is essential in manufacturing, hardware, and precision engineering.
Frequently Asked Questions
1 inch is equal to exactly 25.4 millimeters. This is an exact definition established by the international yard and pound agreement of 1959: 1 inch = 25.4 mm exactly. To convert inches to millimeters, multiply by 25.4. For example, 6 inches × 25.4 = 152.4 mm, and 12 inches (1 foot) × 25.4 = 304.8 mm.
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