Countersink Depth Calculator
ConstructionCalculate the drilling depth needed for a countersink to seat a flat-head screw flush. Enter screw head diameter and countersink angle for exact depth.
Countersink Depth
0.288
Countersink Rim Diameter
0.5
What is a Countersink Depth?
A Countersink Depth Calculator finds the exact drilling depth needed for a countersink to seat a flat-head screw or bolt flush with the surrounding surface, based on the screw head diameter and the countersink tool's included angle. This is a simple but essential piece of trigonometry for woodworking, metalworking, and fastening projects where a flush finish matters.
Since flat-head screws have a cone-shaped underside, the countersink recess must match that cone precisely — drilled to the correct depth so the widest part of the screw head sits exactly level with the surface.
How to use this Countersink Depth calculator
- Enter the Screw Head Diameter in inches — measure this with calipers for best accuracy.
- Select the Countersink Angle matching your screw type: 82° (standard US), 90° (standard metric), or 100°.
- Review the Countersink Depth result.
- Set your drill press or countersink bit's depth stop to this depth.
- Test on scrap material before drilling your final workpiece to confirm a flush fit.
Formula & Methodology
The calculator uses right-triangle trigonometry based on the cone geometry of the countersink: Countersink Depth = (Screw Head Diameter ÷ 2) ÷ tan(Countersink Angle ÷ 2) Worked example: For a 0.5-inch screw head diameter with an 82-degree countersink angle: Half-Angle = 82° ÷ 2 = 41° Countersink Depth = (0.5 ÷ 2) ÷ tan(41°) = 0.25 ÷ 0.8693 ≈ 0.2876 in This means a screw with a 0.5-inch head diameter, using a standard 82-degree countersink, needs a countersink drilled to about 0.288 inches deep for the head to sit perfectly flush with the surface.
Frequently Asked Questions
A countersink is a cone-shaped recess drilled or cut into a material so that a flat-head (countersunk) screw or bolt sits flush with, or below, the surface once installed. Getting the depth right matters because too shallow leaves the screw head proud above the surface, while too deep leaves an unsightly gap or weakens the material around the hole.
Countersink depth is calculated using the screw head diameter and the countersink tool's included angle: depth = (head diameter ÷ 2) ÷ tan(half the included angle). This calculator applies that formula automatically once you enter your screw head diameter and select the countersink angle.
82 degrees is the standard included angle for countersunk screws and fasteners in the US and much of the imperial fastener world, while 90 degrees is more common in metric and European fastener standards. Using the wrong angle tool for your screw type will result in a countersink that doesn't match the screw head's cone shape, leaving either a visible gap or a screw that sits proud.
Check the screw packaging or manufacturer specification, since flat-head (countersunk) screws are manufactured to a specific head angle — most standard US wood and machine screws use an 82-degree head, while many metric and some specialty screws use 90 or 100 degrees.
Drilling too deep causes the screw head to sit below the surface, leaving a visible recessed gap around the screw and potentially weakening the surrounding material, especially in thinner stock — it can also reduce the screw's holding strength if the countersink removes too much material around the shank.
If the countersink isn't deep enough, the screw head will sit proud above the surface rather than flush, which can create a snag hazard, prevent a mating part from seating flush, or simply look unfinished — you'll need to redrill deeper or use a shallower-head screw.
No, this calculator focuses specifically on the countersink cone depth based on the screw head diameter and angle — you'll still need to drill an appropriately sized pilot or clearance hole for the screw shank separately, sized to the screw's shank diameter and the material you're fastening.
Yes, the same geometry applies to any countersunk fastener, including flat-head bolts and machine screws, as long as you know the head diameter and the included angle of the countersink cone — enter the bolt head's diameter just as you would a screw head.
82 degrees is the most common countersink angle for woodworking with standard imperial wood screws in the US, making it the default angle for most countersink bits sold for general carpentry and furniture work.
Measure the screw head diameter as precisely as you can with calipers for the most accurate depth result, since even small errors in head diameter translate directly into depth errors — for critical flush-fit applications, a difference of a few thousandths of an inch can be noticeable.
Yes, it's good practice to test your countersink bit and depth stop setting on a scrap piece of the same material before drilling your final workpiece, since real-world results can vary slightly depending on bit sharpness, material hardness, and drill speed.
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