Countersink Depth
Calculate the exact countersink depth for flat-head screws and bolts. Enter diameter and angle to get the precise conical hole depth for countersinking applications.
About This Calculator
The Countersink Depth Calculator computes the precise depth of a conical countersink hole based on its diameter (the width at the surface) and the included angle of the countersink. This tool is essential for machinists, woodworkers, metalworkers, engineers, and DIY enthusiasts who need to ensure flat-head screws and bolts sit flush with or below the material surface.
The calculation uses the formula: depth = (diameter / 2) / tan(angle / 2). Since the countersink forms a conical shape, basic trigonometry determines the depth from the two known parameters. Simply select your unit (mm or inches), enter the diameter of the hole at the surface, and the countersink angle in degrees. The calculator instantly returns the depth, plus a breakdown showing the half-angle and a comparison chart.
Standard countersink angles vary by region and application: 82° is the most common angle for imperial flat-head screws (used across the US), while 90° is standard for metric flat-head screws (common in India, the UK, and Europe). Other angles such as 60° (for some machine screws), 100° (for thin sheet metal), and 120° (for wood screws) are also supported. The Depth vs Angle chart helps visualize how changing the angle affects the required depth for the same diameter.
Using the correct countersink depth prevents common issues like screw head protrusion (which can snag or cause injury), stripped screw heads from overtightening, poor alignment, and weakening of the surrounding material. Always verify the screw head diameter and recommended angle from the screw manufacturer for best results.
Frequently Asked Questions
What is countersink depth?
Countersink depth is the depth of a conical hole cut into a material so the head of a countersunk screw or bolt sits flush with or below the surface of the surrounding material. It is measured from the material surface to the bottom of the countersink hole.
How do you calculate countersink depth?
Countersink depth is calculated using the formula: depth = (diameter / 2) / tan(angle / 2), where diameter is the width of the countersink hole at the surface, and angle is the included angle of the conical countersink (typically 82° for imperial or 90° for metric flat-head screws).
What is the standard countersink angle for flat-head screws?
The most common countersink angles are 82° for imperial flat-head screws (used in the US) and 90° for metric flat-head screws (common in India, UK, and Europe). Other angles such as 60°, 100°, and 120° are used for specific applications like sheet metal or wood screws.
What is the difference between countersink and counterbore?
A countersink is a conical hole that allows the head of a flat-head screw to sit flush with the material surface. A counterbore is a cylindrical flat-bottomed hole that provides clearance for socket-head cap screws or bolts, where the fastener head sits inside a cylindrical recess rather than a conical one.
Why is accurate countersink depth important?
Accurate countersink depth ensures the screw head fits flush with the surface, providing a secure fit and preventing the screw from loosening. If too shallow, the head protrudes and can catch or cause damage. If too deep, the screw may not grip properly and the material can be weakened.
Can I use this calculator for both metric and imperial units?
Yes, the countersink depth calculator supports both millimeters (mm) for metric and inches for imperial measurements. Simply select your preferred unit before entering the diameter, and the depth result will be displayed in the same unit.
What is the optimal countersink depth for a screw?
The optimal countersink depth depends on the screw size and type. Generally, the depth should be enough to allow the screw head to sit flush with or slightly below the material surface. Use this calculator with the screw head diameter and the standard countersink angle (82° or 90°) to determine the correct depth.
How does the depth change with different countersink angles?
For a given diameter, a smaller countersink angle produces a deeper conical hole, while a larger angle produces a shallower one. For example, with a 10 mm diameter: a 60° angle gives a depth of 8.66 mm, an 82° angle gives 5.76 mm, and a 120° angle gives 2.89 mm. Use the Depth vs Angle chart to visualize this relationship.