Calculate drill point length from drill diameter and point angle (118° by default), or find the diameter or angle, plus total drilling depth to the tip.
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Drill Point Length Formula
For an ideal conical drill point, axial point length is determined by drill diameter and included point angle. Use positive lengths and an included angle greater than 0° and less than 180°. Actual split-point and specialized tip profiles can differ.
- 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 convert to millimeters using exact conversions, then convert to the selected result unit. The included point angle is entered in degrees.
Common Drill Point Angles and Length Factors
The point length factor is the axial length of an ideal conical tip divided by drill diameter. Manufacturer examples include 118° twist drills and 135° split-point drills; angle alone does not specify suitability for a material.
| 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 | Illustrative point geometry |
| 135° | 0.2071 × D | L = 0.2071D | A split-point angle offered on some twist drills |
| 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.
