FREE ENGINEERING CALCULATOR · BILINGUAL
Drill Point Length & Depth Calculator: 118°, 135°, 140°
Calculate drill-point length from diameter and included point angle. Convert between full-diameter hole depth and total tip depth, in millimeters or inches, with a custom point angle.
Enter parameters
Or load an example:
Calculated results
Parameters changed. Select Calculate to update the results.
| Point length L | 3.0043031 mm |
|---|---|
| Full-diameter depth H | 20 mm |
| Total tip depth T | 23.0043031 mm |
| Point length / diameter | 0.30043031 |
Ideal conical point entering a flat surface normally. Depths are positive downward from the top surface. Results exclude machine offsets, tool compensation and extra breakthrough allowance.
Calculation formulas
L = D / [2 tan(θ/2)] · T = H + L · H = T − L
Why add the drill-point length?
The hole narrows through its conical bottom. If the drawing specifies full-diameter depth H, the tip must reach H + L to produce that cylindrical length. The point cross-section gives tan(θ/2) = (D/2)/L.
Example: 12 mm drill, 135°, 25 mm full depth
The point length is about 2.485281 mm and total tip depth about 27.485281 mm. The common quick factor 0.207 is rounded; this calculator uses trigonometry, so it differs slightly from rounded tables.
How do I use this for through and blind holes?
For a blind hole, enter the required cylindrical depth. For theoretical full-diameter breakthrough through a flat plate, use plate thickness as H. Actual machining may require additional allowance. This calculator adds no allowance automatically and does not generate G-code.
Which tools need a different model?
Flat-bottom drills, step drills, asymmetric points and special grinds need their actual tool geometry. Angled entries, cross holes and thin-wall exits are also outside this model. Use the related countersink calculator for a conical recess over an existing pilot hole.
Quick reference
Ideal conical points for a 10 mm diameter drill.
| Included angle | L / D | L (mm) |
|---|---|---|
| 90° | 0.5 | 5 |
| 118° | 0.30043031 | 3.0043031 |
| 120° | 0.288675135 | 2.88675135 |
| 130° | 0.233153829 | 2.33153829 |
| 135° | 0.207106781 | 2.07106781 |
| 140° | 0.181985117 | 1.81985117 |
| 150° | 0.133974596 | 1.33974596 |