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Countersink Depth Calculator

The countersink depth calculator helps you determine the depth of a countersunk hole.

Clear
Countersink depth0.1438 in3.6524 mm below the surface
Countersink diameter0.5 in
Pilot hole diameter0.25 in
Included angle82°the standard for imperial flat-head screws
Depth to the full diameter0.28759 inif the countersink ran to a point
Material thickness0.25 in
Material left below the countersink0.1062 in42.5% of the thickness
Checksensiblea countersink deeper than about 70% leaves too little material

The formula

countersink depth = (Dcs − Dhole) ÷ (2 tan(angle ÷ 2))

Four hole problems, one page

A countersink’s depth follows from simple trigonometry: the cone narrows from the countersink diameter to the hole diameter, and how fast depends on the half angle. Note that 82° is the imperial standard for flat-head screws while metric uses 90° — mixing them leaves the head either proud or sunk.

True position is the one people get wrong most often. GD&T expresses it as a diameter, so the deviation is twice the radial error: being 0.003 out in x and 0.004 in y is a 0.005 radial error but a 0.010 true position deviation.

The clearance and rivet figures are conventions rather than laws, but they are the conventions drawings assume: 1.5 diameters to an edge, 3 diameters between fasteners.