Drill Point Calculator

Instantly find the length of your drill bit’s tip for precision drilling.

What is a Drill Point Calculator?

A drill point calculator is a specialized tool used in engineering and machining to determine the length of the conical tip of a drill bit. This calculation is crucial for achieving precise hole depths, especially in operations where the hole does not go all the way through the material (a “blind hole”) or when calculating the total travel needed for a CNC machine. The length of the drill point must be added to the desired full-diameter depth to ensure the hole is drilled correctly. This tool is indispensable for CNC programmers, machinists, mechanical engineers, and even serious DIY enthusiasts who require high accuracy in their work.

Drill Point Calculator Formula and Explanation

The calculation for the drill point length is based on simple trigonometry. The drill’s tip forms a cone, and by taking a cross-section, we can form a right-angled triangle. The formula is:

L = (D / 2) / tan(A / 2)

This formula allows us to calculate the height of the cone (the drill point length) using its base (the drill diameter) and its angle. Understanding this is key to many milling formulas.

Variables used in the drill point calculation.

Variable	Meaning	Unit (Auto-Inferred)	Typical Range
L	Drill Point Length	mm or inches	Dependent on D and A
D	Drill Diameter	mm or inches	0.1 – 100+
A	Drill Point Angle	Degrees (°)	90° – 140°

Practical Examples

Example 1: Standard General-Purpose Drilling

A machinist needs to drill a hole with a standard 10mm drill bit that has a common 118° point angle.

• Inputs: Drill Diameter (D) = 10 mm, Point Angle (A) = 118°
• Calculation: L = (10 / 2) / tan(118 / 2) = 5 / tan(59°) ≈ 3.00 mm
• Result: The drill point adds 3.00 mm to the total drill depth.

Example 2: Drilling Hard Material

An engineer is drilling into stainless steel with a 0.5-inch drill bit, which requires a flatter 135° point angle for better performance in hard metals.

• Inputs: Drill Diameter (D) = 0.5 in, Point Angle (A) = 135°
• Calculation: L = (0.5 / 2) / tan(135 / 2) = 0.25 / tan(67.5°) ≈ 0.104 in
• Result: The point length is approximately 0.104 inches. This information is vital for programming the correct depth in a CNC G-code program.

How to Use This Drill Point Calculator

1. Enter Drill Diameter: Input the diameter of your drill bit in the first field.
2. Enter Point Angle: Input the included angle of the drill bit’s tip. The most common is 118°, but 135° is also frequently used, especially for harder materials.
3. Select Units: Choose whether your measurements are in millimeters (mm) or inches (in). The calculation will automatically adjust.
4. Interpret Results: The primary result shows the calculated length of the drill point. This is the extra depth you need to drill to achieve a hole with the full diameter at the specified depth. The chart below provides a visual comparison for standard angles.

Key Factors That Affect Drill Point Geometry

• Material Hardness: Harder materials like stainless steel or high-carbon steel require a larger (flatter) point angle (e.g., 135°-140°) to reduce cutting pressure and increase the strength of the cutting edge. Softer materials like aluminum or wood use a smaller (sharper) angle (e.g., 90°-118°).
• Chip Formation: The point angle influences how chips are formed and evacuated from the hole. A larger angle can help with chip flow in certain materials. This is a critical factor in determining the correct speeds and feeds.
• Self-Centering Capability: A 135° angle, especially with a “split point” geometry, is better at starting a hole without a center punch, as it has less tendency to “walk” across the surface. A 118° angle is more prone to walking.
• Cutting Edge Strength: A larger, flatter angle provides a stronger cutting edge, which is more resistant to chipping and wear when drilling hard or abrasive materials.
• Required Hole Accuracy: For high-precision work, knowing the exact point length is non-negotiable for achieving the correct depth and for operations like countersinking.
• Drill Bit Coating: Coatings like Titanium Nitride (TiN) or Titanium Carbonitride (TiCN) increase surface hardness and lubricity, which can influence the optimal point geometry for a given application.

Frequently Asked Questions (FAQ)

1. What is the most common drill point angle?

The most common drill point angle is 118 degrees, which is standard for general-purpose drilling in soft to medium-hard materials like wood, plastic, and mild steel.

2. Why would I use a 135-degree drill bit?

A 135-degree angle is used for drilling harder, tougher materials like stainless steel, high-carbon steel, and cast iron. The flatter angle provides a stronger cutting edge and helps prevent the bit from “walking” when starting a hole.

3. Does this calculator work for both inches and mm?

Yes. You can select your desired unit from the dropdown menu, and the calculator provides the result in the same unit system. The underlying mathematical formula is independent of the unit.

4. How do I measure a drill’s point angle?

You can measure the angle using a protractor or a specialized drill gauge. For a quick visual check, a 118° angle is noticeably sharper than a 135° angle.

5. What is a “split point” drill bit?

A split point bit has a modified tip that includes an extra “split” at the center. This design helps the bit self-center and requires less force to begin drilling, effectively eliminating the need for a center punch.

6. Why is the drill point length important for blind holes?

For a blind hole (one that doesn’t go through the material), the final depth is critical. If a drawing specifies a 20mm deep hole of a certain diameter, you must drill 20mm PLUS the drill point length to ensure the full diameter section is 20mm deep.

7. Can I use this for a tap drill?

Yes. When drilling a hole before tapping threads, achieving the correct depth is important for ensuring the proper thread engagement. Our tap drill size chart can help you find the right diameter, and this calculator helps find the total depth.

8. Is a longer or shorter drill point better?

Neither is universally “better”; they are for different purposes. A shorter point (larger angle, e.g., 135°) is stronger and better for hard metals. A longer point (smaller angle, e.g., 118°) is more aggressive and works well in softer materials.