Countersink Calculator
Find the depth a countersink needs to reach so a flat head screw seats flush with the surface.
Matching angle to your screw standard
82° is the standard included angle for US flat head machine and wood screws (ASME B18.6). Some metric and aerospace flat head fasteners use 90° or 100° instead — check the fastener spec rather than assuming 82° if the screw isn't a standard US flat head.
Diameter is the screw head, not the clearance hole
The countersink's top diameter needs to match the screw's head diameter so the full underside of the head bears against the cone — the smaller clearance hole for the screw's shank is drilled separately, straight through the bottom of the countersink.
Cut shallow first, then check
Countersinking a hair too deep leaves the screw sitting below the surface with no way to fix it short of a bigger screw or a filler; too shallow just needs another light pass. Sneak up on the final depth with a test screw rather than committing to the full calculated depth on the first pass, especially on a finished or visible surface.