Enter the hole diameter (or screw shank diameter), countersink depth, and the countersink angle into the calculator to determine the countersink (top) diameter. This calculator helps in designing and manufacturing processes where countersunk screws are used.

Countersink Diameter Calculator

Enter any 3 values to calculate the missing variable

Countersink Diameter Formula

The following formula is used to calculate the countersink (top) diameter for a conical countersink made to a depth h from a hole (or screw shank/clearance hole) diameter d at the start of the countersink.

CD = d + 2h\tan(\theta/2)

Variables:

  • CD is the countersink (top) diameter
  • d is the hole diameter (often the screw shank/clearance hole diameter at the start of the countersink)
  • h is the countersink depth
  • θ is the countersink included angle (degrees)

To calculate the countersink diameter, add twice the countersink depth multiplied by the tangent of half the countersink angle to the starting hole diameter.

What is a Countersink Diameter?

Countersink diameter is the diameter of the conical feature at the surface of a countersunk hole. It allows a flat-head (countersunk) screw to sit flush with or below the surface. The countersink diameter is larger than the hole (or screw shank/clearance hole) diameter and is determined by the countersink angle and either the countersink depth or the required screw head diameter (depending on your design/specification).

How to Calculate Countersink Diameter?

The following steps outline how to calculate the Countersink Diameter.

  1. First, determine the starting hole diameter (d).
  2. Next, determine the countersink depth (h).
  3. Next, determine the countersink included angle (θ) in degrees.
  4. Next, gather the formula from above: CD = d + 2h tan(θ / 2).
  5. Finally, calculate the Countersink Diameter (CD).
  6. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

hole / screw diameter (d) = 0.25 inches

countersink depth (h) = 0.15 inches

countersink angle (θ) = 82 degrees