Countersink Depth Calculator

in
in
#8 screw shank ≈ 0.164 in.
°
Standard flat-head: 82°; metric: 90°.
Construction

Calculate the countersink hole depth needed for a flat-head screw based on head angle and diameter.

Formula

Depth = (head diam − shank diam) / 2 / tan(half angle)
  • Standard US flat-head screws: 82° included angle.
  • Metric flat-head screws: 90° included angle.
  • Depth is measured from top surface to bottom of countersink.

#8 screw (head 0.375 in, shank 0.164 in), 82°

Inputs
  • Screw Head Diameter: 0.375 in
  • Shank Diameter: 0.164 in
  • Head Angle: 82 °

(0.375−0.164)/2 / tan(41°) ≈ 0.121 in depth.

Frequently asked questions

What countersink angle do I use?
For US standard wood screws, use 82°. For metric, use 90°.