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. If you mean an #8-32 machine screw tap hole, use a #29 drill bit instead.
Hardwood straight bit
1/8 in
Softwood straight bit
7/64 in
Hardwood tapered bit
11/64 in
Softwood tapered bit
5/32 in
#8-32 tap drill
#29 drill bit
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.
#8 screw versus #8-32 screw
A #8 wood screw and an #8-32 machine screw are not the same job. Use this chart for wood screw pilot holes. If you are tapping metal or plastic for an #8-32 machine screw, use the #8-32 tap drill guide.
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 useful when you are installing hinges, cabinet hardware, brackets, or trim.
Frequently asked questions
What size drill bit for a #8 screw?
For a #8 wood screw, use 1/8 inch in hardwood or 7/64 inch in softwood with a straight bit. For an #8-32 tap hole, use a #29 drill bit.
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.