How to use this converter
Select your input format — fractions (like 3/8"), decimal inches (like 0.375"), or millimeters — then type your measurement. The converter shows results in all three formats instantly as you type.
For fractional inputs, you can type simple fractions like "3/8" or mixed numbers like "5 1/2". Use the quick-select buttons for common tape measure fractions you see marked on a standard tape.
This tool is especially useful when working with building materials, hardware specifications, or any project where you need to convert between imperial and metric measurements.
Reading a tape measure
A standard tape measure divides each inch into 16 equal parts. The longest marks after the inch marks represent 1/2 inch. The next longest represent 1/4 inch, then 1/8 inch, and finally the shortest marks represent 1/16 inch.
The trick to reading a tape measure is counting the smallest marks from the nearest inch line. If you count 5 of the smallest (1/16") marks past the 3-inch line, your measurement is 3 5/16". This converter eliminates the guesswork by giving you the decimal and metric equivalents instantly.
Common tape measure conversions
| Fraction | Decimal (in) | Millimeters |
|---|---|---|
| 1/16" | 0.0625" | 1.588 mm |
| 1/8" | 0.125" | 3.175 mm |
| 3/16" | 0.1875" | 4.763 mm |
| 1/4" | 0.25" | 6.35 mm |
| 5/16" | 0.3125" | 7.938 mm |
| 3/8" | 0.375" | 9.525 mm |
| 7/16" | 0.4375" | 11.113 mm |
| 1/2" | 0.5" | 12.7 mm |
| 9/16" | 0.5625" | 14.288 mm |
| 5/8" | 0.625" | 15.875 mm |
| 11/16" | 0.6875" | 17.463 mm |
| 3/4" | 0.75" | 19.05 mm |
| 13/16" | 0.8125" | 20.638 mm |
| 7/8" | 0.875" | 22.225 mm |
| 15/16" | 0.9375" | 23.813 mm |
| 1" | 1.0" | 25.4 mm |
Frequently asked questions
What is 3/8 on a tape measure in decimal?
3/8 of an inch equals 0.375 inches, or 9.525 millimeters. On a tape measure, the 3/8" mark is the third-longest line between inch marks.
How do I convert inches to millimeters?
Multiply the inch value by 25.4. For example, 1/2 inch = 0.5 × 25.4 = 12.7 mm. This converter does this calculation automatically for any measurement you enter.
What are the marks on a tape measure?
The longest marks are full inches. Between them, marks decrease in size for 1/2, 1/4, 1/8, and 1/16 inch increments. The smallest marks on a standard tape measure represent 1/16 of an inch (about 1.6 mm).
How accurate is this converter?
This converter is mathematically precise. It uses the exact conversion factor of 1 inch = 25.4 millimeters, which is the internationally defined standard.