Inches to mm Converter
Mechanical precision conversion for parts and tooling.
How to convert Inches to Millimeters?
In the world of mechanical engineering and manufacturing, the transition between imperial (inches) and metric (mm) units is a daily task. Since the international yard and pound agreement of 1959, the inch has been defined as exactly 25.4 millimeters.
1 Inch (in) = 25.4 Millimeters (mm)
1 Millimeter (mm) = 0.0393701 Inches (in)
Fractional Inch to Metric Table
In mechanical shops, tools like wrenches and drill bits are often sized in fractions. Here are the most common industrial equivalents:
| Fractional Inch | Decimal Inch | Metric (mm) |
|---|---|---|
| 1/16" | 0.0625" | 1.5875 mm |
| 1/8" | 0.1250" | 3.1750 mm |
| 1/4" | 0.2500" | 6.3500 mm |
| 1/2" | 0.5000" | 12.7000 mm |
| 3/4" | 0.7500" | 19.0500 mm |
| 1" | 1.0000" | 25.4000 mm |
Why Precision Matters in Machining
Understanding the difference between decimal systems is vital for high-tolerance work:
- CNC Programming: When translating a drawing from imperial to metric, rounding errors can lead to parts that don't fit (interference) or are too loose (slop).
- Tooling Selection: Using a 13mm wrench on a 1/2" bolt (12.7mm) might work, but it can strip the head over time. Always use the exact tool for the measurement.
- Global Supply Chain: Aerospace and automotive sectors often use a mix of both systems depending on the component's origin, requiring engineers to be fluent in both.
FAQ: Mechanical Measurements
Is 25mm the same as 1 inch?
No. While 25mm is close, a true inch is 25.4mm. That 0.4mm difference is massive in precision engineering and can cause mechanical failure if ignored.
What is a 'thou' in engineering?
A 'thou' (short for a thousandth of an inch) is 0.001 inches, which equals 0.0254 mm. It is the standard unit of tolerance in many US machine shops.