Standard end mill diameters in fractional inch and metric, with decimal and millimeter equivalents. Use it to match a cutter to a feature and to convert between systems.
Fractional inch
| Diameter | Decimal (in) | mm |
|---|---|---|
| 1/16 in | 0.0625 | 1.59 |
| 3/32 in | 0.0938 | 2.38 |
| 1/8 in | 0.1250 | 3.17 |
| 5/32 in | 0.1563 | 3.97 |
| 3/16 in | 0.1875 | 4.76 |
| 1/4 in | 0.2500 | 6.35 |
| 5/16 in | 0.3125 | 7.94 |
| 3/8 in | 0.3750 | 9.52 |
| 1/2 in | 0.5000 | 12.70 |
| 5/8 in | 0.6250 | 15.88 |
| 3/4 in | 0.7500 | 19.05 |
| 1 in | 1.0000 | 25.40 |
Metric
| Diameter | Inch (in) |
|---|---|
| 1 mm | 0.0394 |
| 2 mm | 0.0787 |
| 3 mm | 0.1181 |
| 4 mm | 0.1575 |
| 5 mm | 0.1969 |
| 6 mm | 0.2362 |
| 8 mm | 0.3150 |
| 10 mm | 0.3937 |
| 12 mm | 0.4724 |
FAQ
Why does end mill diameter selection matter beyond just fitting the feature size? Larger diameters are stiffer and can run more aggressive parameters, but they also can’t reach small internal corners or narrow slots, so diameter selection is a balance between rigidity and access to the smallest feature in the part.
The most common sizes; many shops stock these plus reduced-shank and undersize cutters. Convert any size with the Unit Conversion Calculator.