8 mm Drill Bit Size
An 8 mm drill bit is 0.3150 inches. The nearest common fractional drill bit is 5/16 inch, which measures 0.3125 inches or 7.94 mm.
Quick Answer
Decimal
0.3150 in
Metric
8.00 mm
Closest
5/16 inch
8 mm Drill Bit Equivalent Chart
| Size | Decimal Inches | Metric | Note |
|---|---|---|---|
| 8 mm | 0.3150 in | 8.00 mm | Exact size |
| 5/16 inch | 0.3125 in | 7.94 mm | Closest common fractional size |
| O | 0.3160 in | 8.03 mm | Nearby letter drill size |
| 21/64 inch | 0.3281 in | 8.33 mm | Oversize clearance alternative |
Common Uses
Larger anchors, metric bolt clearance, and medium construction holes.
Exact vs Nearest Size
Choose the exact bit for threads, tight hardware fits, dowels, and precision layouts. Use the nearest common equivalent only for rough pilot holes, clearance holes, or material removal where a slight difference is acceptable.
8 mm Drill Bit FAQ
What are the inch and metric dimensions for 8 mm?
8 mm drill bit measures 0.3150 in and 8.00 mm.
What is the closest common equivalent to 8 mm?
5/16 inch is the closest common equivalent listed here. It measures 0.3125 in or 7.94 mm.
Can I substitute another bit for 8 mm?
Use the exact bit size for tap drilling, precision holes, dowels, and manufacturer-specified hardware. A nearby fractional, metric, numbered, or letter drill bit is usually fine only for clearance holes or rough pilot holes.