Drill Point Depth Calculator

A twist drill's point adds length beyond the flat-bottom depth — get the tip length so through-holes actually break through and blind holes hit the depth you meant.

The diameter of the twist drill you're using.
The drill's tip angle — 118° is standard for most general-purpose twist drills.
Only needed for a through-hole — the thickness of the material being drilled.

The formula

Point length = (diameter ÷ 2) ÷ tan(point angle ÷ 2). This is the extra length the conical tip adds beyond where the drill's full diameter (the cylindrical margin) actually reaches — a narrower point angle produces a longer, pointier tip, while a wider angle (closer to flat) produces a shorter one.

Why through-holes need a breakthrough allowance

If you program a through-hole to stop exactly at material thickness, the drill's point hasn't fully broken through the far side yet — the cylindrical margin reaches full diameter only after the point has already traveled its full point length past that surface. Programmed depth for a clean through-hole should be material thickness plus point length (plus a small safety margin), not material thickness alone.

Why blind holes need the opposite correction

A blind hole's "depth" as usually specified means the depth of the flat-bottomed portion at full diameter, but the drill's point extends further than that before the hole even starts — the true bottom of the hole (following the cone down to the drill's centerline) sits deeper than the flat-bottom callout by roughly this same point length. Get this backwards on a blind hole with a tight depth tolerance and the fully-drilled diameter section comes up short.

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