Two calculators in one: countersink depth for flat-head screws, and counterbore diameter/depth for socket-head cap screws. Enter dimensions in whichever consistent unit you prefer (mm or inches) — results use the same unit.
Countersink (Flat Head Screws)
Depth is measured from the surface to where the cone reaches the full head diameter (flush fit). If you want the screw head slightly below the surface, add the extra sink amount directly to this depth.
Counterbore (Socket Head Cap Screws)
Clearance is added to both the diameter and depth so the cap screw head drops in freely without binding. Increase clearance for rough holes or coated fasteners.
Quick Reference: SHCS Head Dimensions (ISO 4762, approx.)
| Size | Head Dia. | Head Height |
|---|---|---|
| M3 | 5.5 | 3.0 |
| M4 | 7.0 | 4.0 |
| M5 | 8.5 | 5.0 |
| M6 | 10.0 | 6.0 |
| M8 | 13.0 | 8.0 |
| M10 | 16.0 | 10.0 |
| M12 | 18.0 | 12.0 |
Values in mm, approximate per ISO 4762 — always check the actual fastener spec sheet for critical fits.
How It Works
A countersink cone widens at a fixed included angle, so the depth needed to reach the full head diameter follows from simple trigonometry: depth = (head diameter − hole diameter) ÷ (2 × tan(angle / 2)). A counterbore is a flat-bottomed cylindrical pocket, so its diameter and depth are just the head dimensions plus clearance — no trig involved.
FAQ
What angle should I use for a countersink? 82° is standard for UTS flat-head screws (ANSI), while 90° is the most common metric/ISO standard. Always match the angle to the screw you are using — a mismatched angle will leave the screw head not fully seated, or will undercut and the head will sit below flush at an angle.
How much counterbore clearance should I use? 0.3–0.5 mm (0.012–0.020 in) on diameter and depth is typical for a free-fitting socket head cap screw in a machined hole.
Related Guides
Thread Calculator · Drill Point Depth Calculator · Hole Pattern Calculator