Calculate drill point length, drill diameter, or point angle from any two values using inch, mm, cm, m, or ft units and formulas.
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Drill Point Length Formula
The drill point length is based on the geometry of the drill tip. The calculator uses the drill diameter and included point angle to solve for the missing value.
- L = drill point length
- D = drill diameter
- A = drill point angle, in degrees
- tan = tangent function
- atan = inverse tangent function
If you enter drill diameter and point angle, the calculator solves for point length. If you enter point length and point angle, it solves for drill diameter. If you enter drill diameter and point length, it solves for point angle.
Length values are converted to inches internally for the calculation, then converted back to the unit you selected for the answer. The point angle is entered in degrees.
Common Drill Point Angles and Length Factors
The point length factor shows how long the drill tip is as a multiple of the drill diameter.
| Point angle | Point length factor | Point length formula | Typical use |
|---|---|---|---|
| 90° | 0.5000 × D | L = 0.5000D | Sharper point, longer tip |
| 118° | 0.3004 × D | L = 0.3004D | Common general-purpose twist drill angle |
| 120° | 0.2887 × D | L = 0.2887D | Close to standard general-purpose geometry |
| 135° | 0.2071 × D | L = 0.2071D | Common split-point angle for harder materials |
| 140° | 0.1820 × D | L = 0.1820D | Flatter point, shorter tip |
Drill Point Length Examples
Example 1: Find point length from diameter and angle
You have a 0.500 in drill with a 118° point angle.
The drill point length is 0.1502 in.
Example 2: Find point length for a metric drill
You have a 10 mm drill with a 135° point angle.
The drill point length is 2.0711 mm.
FAQ
What is drill point length?
Drill point length is the distance from the drill tip to the point where the drill reaches its full diameter. It is the height of the conical point at the end of the drill.
Why does point angle change the point length?
A smaller point angle creates a sharper, longer tip. A larger point angle creates a flatter, shorter tip. For the same drill diameter, a 118° point has a longer point length than a 135° point.
Should point length be included when drilling a blind hole?
Yes, if the hole depth must include the full diameter section. The drill tip reaches deeper than the point where the hole first becomes full diameter. For a blind hole, add the point length when you need to account for the extra depth made by the drill tip.
