Inches to mm Converter: Inches to Millimeters
Convert decimal and fractional inches to exact millimeters instantly.
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How to Use the Inches to mm Converter: Inches to Millimeters
- 1Type fractional or decimal blueprint inches into the measurement box.
- 2Specify desired tolerance decimals for CNC machining or CAD import.
- 3Inspect the calculated metric millimeter dimensions.
- 4Copy the millimeter value directly into your CAM toolpath generator.
Formula & How It Works
Inches to Millimeters Formula
Multiply inches by 25.4.
Worked Examples
CNC Endmill Diameter
Input: 0.25 in (1/4 in)
Explanation: 0.25 * 25.4 = 6.35 mm.
Aluminum Plate Stock
Input: 0.75 in (3/4 in)
Explanation: 0.75 * 25.4 = 19.05 mm.
3D Printer Bed Standoff
Input: 1.5 in
Explanation: 1.5 * 25.4 = 38.10 mm.
Frequently Asked Questions
Is 1 inch legally defined as exactly 25.4 millimeters?▼
Yes, the 1959 International Yard and Pound Agreement legally standardized 1 inch as precisely 25.4 mm.
How do you convert 3/8 inch into millimeters for drilling?▼
3/8 is 0.375 decimal inches; 0.375 * 25.4 = 9.525 millimeters.
What is the metric size of a 1/4-20 hardware bolt?▼
A 1/4-inch bolt shank diameter measures exactly 6.35 mm.
Why does aerospace manufacturing prefer millimeters over inches?▼
Metric units eliminate complex fractional denominators, simplifying statistical process control and ISO tolerances.
Does Toolzy preserve CAD drafting precision?▼
Yes, calculations utilize high-precision decimal floating point without rounding loss.
Quick Reference & Conversion Table
| Fractional Inch | Decimal Inch | Exact Millimeters (mm) |
|---|---|---|
| 1/16 in | 0.0625 in | 1.5875 mm |
| 1/8 in | 0.1250 in | 3.1750 mm |
| 1/4 in | 0.2500 in | 6.3500 mm |
| 1/2 in | 0.5000 in | 12.7000 mm |
| 1 in | 1.0000 in | 25.4000 mm |
⚠️ Common Pitfalls to Avoid
- •Using 25 instead of 25.4 mm, introducing an unacceptable 1.6% mechanical tolerance error on precision machined parts.
- •Misinterpreting fractional drill bit callouts when programming metric G-code.
💡 Practical Real-World Uses
- •Programming metric CNC vertical machining centers from imperial aerospace blueprints.
- •Calibrating 3D printer slicing profiles for American hardware fasteners.
- •Selecting metric drill bits when tapping American Unified National Coarse (UNC) bolt threads.
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