5/8 inch equals 15.875 millimeters. This conversion is precise because one inch equals exactly 25.4 millimeters in the metric system.
Converting fractional inches to millimeters requires multiplying the decimal equivalent of the fraction by 25.4. For 5/8 inch:
5 ÷ 8 = 0.625
0.625 × 25.4 = 15.875mmThis method works for any fractional inch measurement. The U.S. National Institute of Standards and Technology provides official conversion guidelines.
| Fractional Inch | Decimal Equivalent | Millimeter Equivalent |
|---|---|---|
| 1/8 | 0.125 | 3.175 |
| 3/16 | 0.1875 | 4.7625 |
| 1/4 | 0.25 | 6.35 |
| 5/16 | 0.3125 | 7.9375 |
| 3/8 | 0.375 | 9.525 |
| 7/16 | 0.4375 | 11.1125 |
| 1/2 | 0.5 | 12.7 |
| 9/16 | 0.5625 | 14.2875 |
| 5/8 | 0.625 | 15.875 |
| 11/16 | 0.6875 | 17.4625 |
| 3/4 | 0.75 | 19.05 |
| 13/16 | 0.8125 | 20.6375 |
| 7/8 | 0.875 | 22.225 |
| 15/16 | 0.9375 | 23.8125 |
This measurement appears frequently in construction, woodworking, and mechanical applications. For example:
I once built a bookshelf using 5/8 inch plywood for the shelves. The precise conversion to millimeters helped ensure the European-made hardware I ordered would fit perfectly.
People often confuse 5/8 inch with 1/2 inch (12.7mm) or 3/4 inch (19.05mm). Always verify measurements before cutting materials.
Another mistake is rounding 5/8 inch to 16mm. While close, this inaccuracy can cause problems in precision work. Always use the exact 15.875mm measurement for critical applications.
Fractional inches remain common in U.S. construction and manufacturing, while decimal measurements are standard in scientific contexts. Some industries use both systems.
For example, a machinist might specify a part dimension as 0.625 inches in their CAD software, but document it as 5/8 inch on the blueprint for compatibility with traditional measuring tools.
When converting between systems, always check which format your specific application requires. Some measuring tools, like digital calipers, can display both fractional and decimal measurements.