# Countersink Depth Calculator

URL: https://speedycalculator.com/calculators/construction/countersink-depth/
Last updated: 2026-10-25

> The countersink depth calculator finds how deep to cut a countersink to reach a given diameter for the countersink angle, measured from the surface to the tip and to the edge of the pilot hole.

## Inputs

- Countersink diameter (mm, in, cm)
- Countersink angle
- Pilot hole diameter (mm, in, cm)

## Results

- Depth to cone tip
- Depth to edge of pilot hole

## Formula

```
Depth to cone tip = (D ÷ 2) ÷ tan(angle ÷ 2)
Depth below surface to the hole edge = (D − d) ÷ (2 × tan(angle ÷ 2))
```

## Explanation

Flat-head screws sit flush only if the countersink is the right diameter. Countersinks come in standard included angles – 82° for inch flat-head screws, 90° for metric, 100° for aerospace rivets, 118° and 120° for some other uses. Machinists set depth stops rather than measuring the diameter, so converting diameter to depth is handy.

### How to use the Countersink Depth Calculator

- **Countersink diameter**
- **Countersink angle**
- **Pilot hole diameter**
- Every result field is editable: type into **Depth to cone tip** and **Countersink diameter** plus every other field update to match.

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the countersink diameter at the surface, the angle and the pilot hole diameter. Type a depth into the result to find the diameter it produces.

### Tips for an accurate estimate

- Measure angles with a digital angle finder or sliding bevel, not by eye.
- Make a test cut in scrap before cutting expensive stock.
- Small angle errors add up over many joints – check the first assembly before cutting the rest.
- Keep a written list of the dimensions and angles you set on the saw or machine.

### Common mistakes to avoid

- Reading the saw scale as the angle from the edge rather than from square.
- Rounding intermediate results too early.
- Mixing degrees and percent grade.

### Inputs explained

FieldWhat to enterCountersink diameterUnits: mm, in, cmCountersink angleChoose one: 82° (inch flat-head screws), 90° (metric screws), 100° (aircraft rivets), 110° …Pilot hole diameterUnits: mm, in, cm

### What each result means

- **Depth to cone tip** = ([Countersink diameter]÷2)÷tan(rad([Countersink angle]÷2))
- **Depth to edge of pilot hole** = max([Countersink diameter] - [Pilot hole diameter], 0)÷(2×tan(rad([Countersink angle]÷2)))

### Example values

How the main result changes when **Countersink diameter** changes and everything else stays at the example values above:

Countersink diameter (mm)Depth to cone tip (mm)6394.5126157.51892412

## Worked example

Inputs — Countersink diameter: 12 mm; Countersink angle: 90° (metric screws); Pilot hole diameter: 6.6 mm.

Results — **Depth to cone tip = 6 mm**; Depth to edge of pilot hole = 2.7 mm.

## FAQ

**What angle is a countersink?**
82° for unified (inch) flat-head screws, 90° for ISO metric flat-head screws, 100° for many aerospace rivets.

**How deep should a countersink be?**
Deep enough that the head finishes flush or slightly below the surface – use the head diameter as the countersink diameter.

**What formula does the Countersink Depth Calculator use?**
Depth to cone tip = (D ÷ 2) ÷ tan(angle ÷ 2).