Countersink Depth Calculator

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Walk-through

How to Use This Calculator

4 steps

1

Enter the screw head diameter

Measure or look up the widest point of the flat or oval screw head and enter it, in inches, in the Screw head diameter field.

2

Choose the included angle

Select 82° (US standard flat head), 90° (metric/European standard), 100° (structural/self-tapping), or 120° (rivets/heavy duty) to match your fastener.

3

Add a below-flush offset (optional)

The reported depth is from the surface to the theoretical cone apex. Actual conical-wall depth above a pilot bore is (head diameter − bore diameter)/(2 × tan(angle/2)); the bore and actual screw geometry must be known. At D=0.5 in, bore=0.25 in and 90°, apex depth is 0.25 in and wall depth is 0.125 in.

4

Read the countersink depth

The result updates instantly, showing the depth to drill or machine and the diameter the countersink reaches at that depth.

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Reference

Formula & Methodology

2 formulas

Countersink depth

Depth = (Head diameter ÷ 2) ÷ tan(Included angle ÷ 2) + Offset

The reported depth is from the surface to the theoretical cone apex. Actual conical-wall depth above a pilot bore is (head diameter − bore diameter)/(2 × tan(angle/2)); the bore and actual screw geometry must be known. At D=0.5 in, bore=0.25 in and 90°, apex depth is 0.25 in and wall depth is 0.125 in.

Diameter at depth

Diameter at depth = Head diameter + 2 × Offset × tan(Included angle ÷ 2)

When an offset is added, the countersink must be cut wider than the screw head diameter to keep the same cone angle down to the extra depth. This is the diameter of the cut at the bottom of that extra depth.

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Glossary

Key Terms Explained

6 terms

Countersink The reported depth is from the surface to the theoretical cone apex. Actual conical-wall depth above a pilot bore is (head diameter − bore diameter)/(2 × tan(angle/2)); the bore and actual screw geometry must be known. At D=0.5 in, bore=0.25 in and 90°, apex depth is 0.25 in and wall depth is 0.125 in.

Included angle The full angle at the apex of the countersink cone, matching the angle of the screw head. Common values are 82° (US standard), 90° (metric), 100°, and 120°.

Flush The screw head sits exactly level with the surrounding surface once seated — no offset (offset = 0).

Head diameter The reported depth is from the surface to the theoretical cone apex. Actual conical-wall depth above a pilot bore is (head diameter − bore diameter)/(2 × tan(angle/2)); the bore and actual screw geometry must be known. At D=0.5 in, bore=0.25 in and 90°, apex depth is 0.25 in and wall depth is 0.125 in.

CSK depth Shop shorthand for countersink depth — the distance from the work surface down to where the countersink reaches the screw head's diameter.

Screw head The top of the fastener that the countersink accommodates. Flat and oval heads are conical and countersink-compatible; pan, round, and truss heads are not — they sit on top of the surface instead.

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Scenarios

Real-World Examples

3 worked examples

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DIY furniture builder

1/2 in flat-head screw, 82° countersink, flush

Head diameter 0.5 in Included angle 82° Offset 0 in (flush)

The reported depth is from the surface to the theoretical cone apex. Actual conical-wall depth above a pilot bore is (head diameter − bore diameter)/(2 × tan(angle/2)); the bore and actual screw geometry must be known. At D=0.5 in, bore=0.25 in and 90°, apex depth is 0.25 in and wall depth is 0.125 in.

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Machinist comparing standard angles

Same 1/2 in head, but at 90° instead of 82°

Head diameter 0.5 in Included angle 90° Offset 0 in (flush)

At 90°, half the angle is exactly 45°, where tangent equals 1 — so depth simplifies to exactly half the head diameter divided by 2, or 0.25 in. Because 90° is a wider angle than 82°, the same head diameter needs a noticeably shallower countersink: 0.25 in versus 0.288 in.

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Cabinetmaker sinking a screw for filling

#8 screw, 82° countersink, recessed 1/16 in below flush

Head diameter 0.309 in (#8 screw) Included angle 82° Offset 0.0625 in below flush

The reported depth is from the surface to the theoretical cone apex. Actual conical-wall depth above a pilot bore is (head diameter − bore diameter)/(2 × tan(angle/2)); the bore and actual screw geometry must be known. At D=0.5 in, bore=0.25 in and 90°, apex depth is 0.25 in and wall depth is 0.125 in.

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Reference

Cite This Calculator

APA & MLA

Use either format to cite this calculator in a paper, report, or resource list.

APA

MLA

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Deep Dive

Understanding the Countersink Depth Calculator

3 chapters · 3 min read

The reported depth is from the surface to the theoretical cone apex. Actual conical-wall depth above a pilot bore is (head diameter − bore diameter)/(2 × tan(angle/2)); the bore and actual screw geometry must be known. At D=0.5 in, bore=0.25 in and 90°, apex depth is 0.25 in and wall depth is 0.125 in.

How the calculation works

The reported depth is from the surface to the theoretical cone apex. Actual conical-wall depth above a pilot bore is (head diameter − bore diameter)/(2 × tan(angle/2)); the bore and actual screw geometry must be known. At D=0.5 in, bore=0.25 in and 90°, apex depth is 0.25 in and wall depth is 0.125 in.

Choosing the right included angle

82° is the long-standing US standard for flat-head machine screws (ANSI/ASME B18.6.2) and flat-head wood screws (ANSI/ASME B18.6.1), so it's the default angle for most American hardware. 90° shows up on metric and European fasteners (ISO/DIN standards) and on some structural and aerospace applications. 100° and 120° are less common but appear on certain self-tapping screws, structural fasteners, and rivets. Using the wrong angle for a given screw leaves the head either proud of the surface (countersink too shallow or too narrow an angle) or sunk unevenly with a visible gap around the head (countersink too wide an angle).

When to add a below-flush offset

The reported depth is from the surface to the theoretical cone apex. Actual conical-wall depth above a pilot bore is (head diameter − bore diameter)/(2 × tan(angle/2)); the bore and actual screw geometry must be known. At D=0.5 in, bore=0.25 in and 90°, apex depth is 0.25 in and wall depth is 0.125 in.

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Questions

Frequently Asked Questions

6 questions

What is the countersink depth formula?+

The reported depth is from the surface to the theoretical cone apex. Actual conical-wall depth above a pilot bore is (head diameter − bore diameter)/(2 × tan(angle/2)); the bore and actual screw geometry must be known. At D=0.5 in, bore=0.25 in and 90°, apex depth is 0.25 in and wall depth is 0.125 in.

82° vs 90° countersink — which should I use?+

82° is the US standard included angle for flat-head machine screws and wood screws. 90° is common on metric and European fasteners, and on some structural and aerospace applications. Always match the angle to your screw's actual head angle — a mismatched angle leaves the head proud or unevenly sunk.

What does "flush" mean here?+

The reported depth is from the surface to the theoretical cone apex. Actual conical-wall depth above a pilot bore is (head diameter − bore diameter)/(2 × tan(angle/2)); the bore and actual screw geometry must be known. At D=0.5 in, bore=0.25 in and 90°, apex depth is 0.25 in and wall depth is 0.125 in.

How do I sink a screw below flush?+

The reported depth is from the surface to the theoretical cone apex. Actual conical-wall depth above a pilot bore is (head diameter − bore diameter)/(2 × tan(angle/2)); the bore and actual screw geometry must be known. At D=0.5 in, bore=0.25 in and 90°, apex depth is 0.25 in and wall depth is 0.125 in.

What are common screw head diameters?+

For flat-head machine screws: #4 ≈ 0.211 in, #6 ≈ 0.26 in, #8 ≈ 0.309 in, #10 ≈ 0.359 in, #12 ≈ 0.41 in, and 1/4 in ≈ 0.492 in. The By Screw Size tab lists these with the depth pre-computed at your chosen angle, and lets you apply one with a click.

What units does this calculator use?+

Inches by default — but the formula is a pure ratio with no unit conversion baked in, so entering millimeters for the head diameter and offset returns the depth in millimeters too. Just stay consistent with one unit at a time.

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Calculator topicCountersink Depth

Countersink Depth Calculator

How to Use This Calculator

Enter the screw head diameter

Choose the included angle

Add a below-flush offset (optional)

Read the countersink depth

Formula & Methodology

Key Terms Explained

Real-World Examples

Cite This Calculator

Understanding the Countersink Depth Calculator

How the calculation works

Choosing the right included angle

When to add a below-flush offset

Frequently Asked Questions

Get a branded PDF of your results

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Guides & articles

Glossary terms