Countersink Depth Calculator

Inputs

Included angle (A)

Common: 82° (UNC flat head), 90° (metric/ISO), 100°, 120°.

Top (rim) diameter (D_top)

Desired diameter of the countersink at the surface (the rim).

Existing hole diameter (D_hole)

Pilot/through hole diameter; 0 for cutting into solid.

Default result

Countersink depth(z)

2.5mm

Pass

Axial depth below the surface (or below the pilot-hole rim).

Also computed

Chamfer width(w)3.536mm

Width measured along the cone face (slant length).

Method notes 4 notes

Depth z = (D_top − D_hole) / (2·tan(A/2)) is measured from the surface (or from the pilot-hole rim), down to where the cone reaches the top diameter.
The cone diameter grows with depth as D = D_hole + 2·z·tan(A/2); cutting into solid sets D_hole = 0.
The machine Z-depth from the tool tip differs from this surface depth by the countersink tool’s own geometry (tip flat, point or pre-existing pilot), so set Z off the rim diameter you measure, not the tip.
Chamfer width w = (D_top − D_hole) / (2·sin(A/2)) is the contact length along the cone face — useful for flat-head screw seating.