Calculators
Countersink Calculator
Calculate the cutter depth to open a countersink to a target diameter at 82° (inch flat head) or 90° (metric) — so a flat-head screw sits flush.
Last verified: 2026-07-09
A countersink is a cone that lets a flat-head screw sit flush. Set the countersink diameter to the screw's head diameter and pick the included angle (82° for inch flat-head screws, 90° for metric) to get the cutter plunge depth.
Units
Cutter Z depth
0.138in
Depth = (countersink Ø − through-hole Ø) ÷ (2 · tan(angle ÷ 2)). Set the countersink diameter to the flat-head screw's head diameter so the head sits flush. 82° is standard for inch flat-head screws, 90° for metric.
Frequently asked
- What angle for a flat-head screw?
- 82° included for inch (ANSI) flat-head screws and 90° for metric (ISO) flat-head screws. Match the countersink angle to the screw or the head won't seat flush.
- How do I know the countersink diameter?
- Use the flat-head screw's head diameter (plus a hair for flush/below-flush). Setting the countersink diameter to the head diameter puts the head level with the surface.
Sources
- Cone geometry: depth = (sink Ø − hole Ø) ÷ (2 · tan(angle ÷ 2))