ENGINEERING CALCULATOR · FORMULAS INCLUDED
Countersink Depth Calculator
Find the axial depth of a conical countersink from pilot diameter, major diameter and included angle, or solve for diameter from depth. Supports mm and inches.
Input parameters
Calculated results
Inputs changed. Calculate again to refresh the result.
| Axial depth h | 3 mm |
|---|---|
| Major diameter D | 12.6 mm |
| Pilot diameter d | 6.6 mm |
| Radial chamfer width (D−d)/2 | 3 mm |
| Included angle | 90 ° |
h runs from the workpiece surface to the intersection of cone and pilot hole. It is not the total travel of the cutter tip from the surface.
Countersink depth formula
h = (D − d) / [2 tan(θ/2)] · D = d + 2h tan(θ/2)
D is the major diameter at the surface, d the pilot diameter and θ the included angle. All lengths must use the same unit. At 90°, h = (D − d)/2: radial chamfer width equals axial depth.
The equation follows from the right triangle in the section view. It assumes a straight cone and cylindrical pilot hole; cutter radii, runout, burrs and screw-head tolerances are excluded.
Example: 12.6 mm major diameter, 6.6 mm pilot
At a 90° included angle, h = (12.6 − 6.6)/2 = 3.000 mm. At 82°, the same diameters require about 3.451 mm. This demonstrates geometry; it is not a universal machining specification for a particular screw.
Angles, depth and drawing notes
Which angle: 82°, 90° or 100°?
Match the fastener and drawing. 82° is common for inch flat-head screws, 90° for metric, and 100° for some aerospace fasteners. Do not select the angle from units alone.
Is this the CNC tool-tip plunge depth?
No. h is the axial length of the conical section above the existing hole. Tool-tip position also depends on cutter tip diameter, tool-length offset and the touch-off reference.
Counterbore or countersink?
A counterbore is a flat-bottom recess for a cylindrical head. A countersink is conical for a matching flat-head screw. Use the counterbore chart and drawing for cylindrical recesses; this angle formula does not apply.