👤 By whycalculator Team 📅 Last Updated March, 2026
1/8 Inch to mm
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Working with fractional inches like 1/8, 3/8, 1/2 or 5/8 can be frustrating—especially when you need precise metric conversions. This 1/8 inches to mm calculator makes it simple by letting you enter any fractional inch value and instantly convert it to millimeters. Whether you’re measuring for construction, crafts, or science projects, this tool ensures accuracy without manual math.
Just type the numerator and denominator, and get your mm result in seconds.
What is 1/8 Inch?
The 1/8 inch is a common fractional measurement used primarily in the imperial system, which is still widely used in the United States, Canada, and a few other countries.
- It means one part out of eight equal parts of an inch.
Mathematically:
1/8 inch = 0.125 inch
Where is 1/8 Inch Used?
1/8 inch measurements are frequently used in:
- Woodworking – to cut plywood pieces precisely.
- Metalworking – for drilling or shaping metal parts.
- Home construction – for measuring wall gaps.
- Sewing and quilting – especially for seam allowances.
- Plumbing and piping – small adjustments in pipe length or fittings.
Conversion Formula
To convert inches to millimeters (mm), use the standard formula:
mm = inches × 25.4
So for 1/8 inch:
mm = 1/8 × 25.4 = 0.125 × 25.4 = 3.175 mm
Answer:
1/8 inch = 3.175 mm
More Examples
Example 1: Convert 3/8 inch to mm
3/8 = 0.375 inch
0.375 × 25.4 = 9.525 mm
Example 2: Convert 5/8 inch to mm
5/8 = 0.625 inch
0.625 × 25.4 = 15.875 mm
| Inches | Fraction | Millimeters (mm) |
|---|---|---|
| 0.125 | 1/8″ | 3.175 mm |
| 0.250 | 2/8″ (1/4″) | 6.350 mm |
| 0.375 | 3/8″ | 9.525 mm |
| 0.500 | 4/8″ (1/2″) | 12.700 mm |
| 0.625 | 5/8″ | 15.875 mm |
| 0.750 | 6/8″ (3/4″) | 19.050 mm |
| 0.875 | 7/8″ | 22.225 mm |
| 1.000 | 8/8″ (1″) | 25.400 mm |
| 1.125 | 9/8″ (1 1/8″) | 28.575 mm |
| 1.250 | 10/8″ (1 1/4″) | 31.750 mm |
| 1.375 | 11/8″ (1 3/8″) | 34.925 mm |
| 1.500 | 12/8″ (1 1/2″) | 38.100 mm |
| 1.625 | 13/8″ (1 5/8″) | 41.275 mm |
| 1.750 | 14/8″ (1 3/4″) | 44.450 mm |
| 1.875 | 15/8″ (1 7/8″) | 47.625 mm |
Why Convert 1/8 Inch to Mm?
Many industries, especially outside the US, use the metric system (mm, cm, meters) for standardization and precision.
Converting 1/8 inch to mm is important when:
- Working with international suppliers or clients.
- Using metric-only tools or machines.
- Needing a digital/technical readout in mm.
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