5/16 inch Drill Bit Size
A 5/16 inch drill bit is 0.3125 inches or 7.94 mm. It is the closest common fractional size to an 8 mm drill bit.
Quick Answer
Decimal
0.3125 in
Metric
7.94 mm
Closest
8 mm
5/16 inch Drill Bit Equivalent Chart
| Size | Decimal Inches | Metric | Note |
|---|---|---|---|
| 5/16 inch | 0.3125 in | 7.94 mm | Exact size |
| 8 mm | 0.3150 in | 8.00 mm | Closest common metric size |
| O | 0.3160 in | 8.03 mm | Nearby letter drill size |
| 9/32 inch | 0.2813 in | 7.14 mm | Smaller fractional option |
Common Uses
Medium fasteners, larger anchors, and general 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.
5/16 inch Drill Bit FAQ
What are the inch and metric dimensions for 5/16 inch?
5/16 inch drill bit measures 0.3125 in and 7.94 mm.
What is the closest common equivalent to 5/16 inch?
8 mm is the closest common equivalent listed here. It measures 0.3150 in or 8.00 mm.
Can I substitute another bit for 5/16 inch?
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.