Calculate drill tip length, tip angle, or drill diameter from any two inputs, and find required drill travel for a target hole depth.

Full included angle. Standard jobber drills are 118°, hard-metal drills 135°, spot drills usually 90°.

Full-diameter hole depth
Blank omits travel. Depth is measured from the entry surface to where the full diameter ends.

Drill Tip Length Formula

The following examples use an ideal symmetric conical drill point. The axial point length runs from the tip to the full diameter; real chisel edges, split points and special grinds may differ from this model.

DTL = D / 2 / Tan(A / 2)
  • Where DTL is the Drill Tip Length (in)
  • D is the drill diameter (in) 
  • A is the full included point angle in degrees, strictly between 0° and 180°. 

To calculate a drill tip length, divide the diameter by 2, then divide again by the tangent of half the included point angle, using degree mode. Diameter and tip length use the same units. Ideal tip travel for a specified full-diameter hole depth is that depth plus the point length; verify the actual tool geometry, stock clearance and machine limits separately.

How to Calculate Drill Tip Length?

The following example problems outline how to calculate Drill Tip Length.

Example Problem #1:

  1. First, determine the drill diameter (in).
    • The drill diameter (in) is given as 5.
  2. Next, determine the tip angle (degrees).
    • The tip angle (degrees) is provided as 30.
  3. Finally, calculate the Drill Tip Length using the equation above: 

DTL = D/2/Tan(A/2)

The values provided above are inserted into the equation below and computed.

DTL = 5/2/tan(15deg) = 9.33 (in)

Example Problem #2: 

For this problem, the variables required are provided below:

drill diameter (in) = 6

tip angle (degrees) = 45

Test your knowledge using the equation and check your answer with the calculator.

DTL = D/2/Tan(A/2) = ?