Countersink Depth Calculator

How to use the countersink depth calculator

What this calculator does. This tool estimates the axial depth of an ideal conical countersink. It uses the opening diameter and the full included angle to solve a right-triangle relationship through the centerline. The result is a geometric depth, not a recommendation for a particular screw, cutter, material, tolerance, or manufacturing process. Real parts may also require allowance for an existing pilot hole, tip truncation, runout, coating, or the actual screw-head dimensions.

When to use it. Use it when laying out a countersunk screw so the head can sit flush, checking a drawing before machining, comparing cutters with different included angles, or converting a specified diameter and angle into a depth for inspection. It is also useful for quick classroom or workshop trigonometry checks.

How to calculate. The calculator opens with a ready-to-use demonstration: a 12 mm diameter and a 90° included angle, producing a 6 mm depth and an immediately available XLSX workbook. To use your own values:

1. Replace Countersink diameter with the measured or specified full opening diameter.
2. Select the matching diameter unit. Changing the unit converts the current value rather than merely relabeling it.
3. Enter the full Included angle, then choose degrees or radians.
4. Select the Depth display unit for the result and workbook.
5. Read the primary depth, supporting values, and calculation breakdown. Choose Download Excel to export the current validated state. Reset clears the demonstration and may disable export until complete valid values are entered again.

Input guide. Countersink diameter is required, accepts a plain positive decimal such as 12, and can be expressed in millimeters, centimeters, meters, or inches. Do not enter a radius or a screw's nominal thread diameter unless it truly equals the countersink opening. A larger diameter increases depth in direct proportion when the angle stays fixed. Included angle is required and must be greater than zero and less than 180 degrees, or the equivalent in radians. A realistic example is 90°. Smaller included angles produce deeper cones; angles near 180° produce shallow cones. A common mistake is entering the half-angle instead of the full included angle. Depth display unit is required as a presentation choice; it changes the displayed and exported unit while preserving the same physical depth.

Output guide. Countersink depth is the axial distance from the surface plane to the ideal cone point. Radius is half the opening diameter. Half-angle is the angle used by the tangent function. Diameter-to-depth ratio shows how many depth units fit into one diameter; it depends only on angle. Included angle repeats the normalized angle in degrees. The Calculation breakdown lists the radius, half-angle, tangent, and final division used to obtain the depth. These are exact geometric relationships subject only to displayed rounding.

Worked example. With a 12 mm diameter and 90° included angle, the radius is 12 ÷ 2 = 6 mm. The half-angle is 90° ÷ 2 = 45°, and tan(45°) = 1. Therefore depth = 6 ÷ 1 = 6.00 mm. The first-open result, table, live summary, and exported workbook all use these same values.

Learn more. The underlying calculation is right-triangle trigonometry; OpenStax explains the tangent relationship in its right-triangle trigonometry lesson. For unit discipline, NIST provides an authoritative overview of SI units of length.