Quick answer
For a #8 wood screw, use a 1/8 inch straight bit in hardwood or a 7/64 inch straight bit in softwood. With tapered bits, use 11/64 inch for hardwood or 5/32 inch for softwood.
Hardwood straight bit
1/8 in
Softwood straight bit
7/64 in
Hardwood tapered bit
11/64 in
Softwood tapered bit
5/32 in
Most common #8 screw pilot hole
The quick answer most DIYers need is 1/8 inch for hardwood and 7/64 inch for softwood when using a regular straight drill bit.
Countersink size
A 3/8 inch countersink is a common match for a flat-head #8 wood screw.
Useful tools for this job
A #8 countersink bit is a strong exact-match buy if the user is installing hinges, cabinet hardware, brackets, or trim.
Frequently asked questions
What if the #8 screw is hard to drive?
Stop and enlarge the pilot hole slightly. Forcing a screw can split the wood, strip the head, or snap the screw.