What Is Drill Tip Length?
Drill tip length is the axial distance from the outer diameter edge of the drill point to the apex along the centerline of the drill. Geometrically, the drill point is a cone, and tip length is the cone height. In practical terms, this value tells you how much extra depth the pointed end adds before a full-diameter hole is established.
Many programmers, setup machinists, and toolmakers use tip length when they need tighter depth control. If your print specifies a minimum full-diameter depth, simply commanding that nominal depth is often not enough. The conical tip can leave an undercut bottom or a partial diameter zone, so understanding tip length helps you compensate correctly in CAM and at the control.
Drill Tip Length Formula and Geometry
The standard formula for drill tip length is:
Tip Length = (Drill Diameter / 2) ÷ tan(Point Angle / 2)
Where:
- Drill Diameter is the nominal diameter of the drill.
- Point Angle is the included angle at the drill tip (for example, 118° or 135°).
- tan uses the half-angle in degrees.
This comes directly from right-triangle trigonometry. Split the cone into two equal halves through the centerline, and each half gives a right triangle with opposite side equal to the radius and adjacent side equal to tip length. Rearranging gives the formula above.
Why This Formula Matters
Without tip compensation, holes may fail depth requirements, thread engagement may be reduced, and mating components can bottom out unexpectedly. Tip length is also relevant in through-holes where breakout quality matters on the exit face. In short, this small geometric number has outsized impact on dimensional reliability.
118° vs 135° Drill Point Angles
The two most common general-purpose point angles are 118° and 135°. For a given diameter, a 135° point has a shorter tip length than a 118° point because the cone is “blunter.” This can reduce required extra travel to reach full diameter, but cutting behavior also depends on material, lip relief, web thickness, coating, and machine rigidity.
- 118° point: Traditional general-purpose profile, commonly seen in standard twist drills.
- 135° point: Often preferred for harder materials and reduced wandering at entry, especially when split-point geometry is used.
When switching tools but keeping a similar process, recalculating tip length is a quick way to protect feature depth and avoid first-piece surprises.
How to Use This Drill Tip Length Calculator
- Enter the drill diameter.
- Enter the included point angle (or use 118°/135° quick buttons).
- Select units (mm or inches).
- Click Calculate Tip Length.
The result is displayed in your selected unit with optional cross-unit conversion. You also see half-angle and radius so the math is easy to verify on the fly.
Example Calculation
If drill diameter is 10 mm and point angle is 118°:
Tip Length = (10 / 2) ÷ tan(118 / 2) = 5 ÷ tan(59°) ≈ 3.004 mm
So the drill point extends about 3.004 mm axially from full diameter edge to apex.
Quick Reference Chart (Approximate)
| Diameter | Tip Length @ 118° | Tip Length @ 135° |
|---|---|---|
| 3 mm | 0.901 mm | 0.621 mm |
| 6 mm | 1.802 mm | 1.243 mm |
| 8 mm | 2.403 mm | 1.657 mm |
| 10 mm | 3.004 mm | 2.071 mm |
| 12 mm | 3.605 mm | 2.485 mm |
| 1/4 in | 0.0757 in | 0.0522 in |
| 3/8 in | 0.1136 in | 0.0783 in |
| 1/2 in | 0.1514 in | 0.1044 in |
Values are computed from ideal geometry. Real tools may vary slightly due to grinding tolerances, split points, web thinning, wear, and re-sharpening condition.
Where Drill Tip Length Is Used in Real Work
1) Blind-Hole Depth Programming
When the drawing calls out a minimum cylindrical depth, you typically add tip length to your programmed Z endpoint. This ensures the specified full diameter exists across the required depth, not just a conical partial section.
2) Thread Preparation
For tapped holes, insufficient drilled depth can reduce thread count or cause the tap to push into the cone zone early. Tip-length-aware drilling supports consistent thread engagement and lowers risk of broken taps in blind features.
3) Breakthrough Control in Through-Holes
In thin walls or plate work, knowing cone geometry helps control burr formation and exit behavior. It also improves prediction of when full diameter breaks through, which is useful for peck strategy and feed transition planning.
4) CAM Standardization and Setup Sheets
Many teams place the formula directly in templates so programmers and operators can apply the same depth logic every time. This reduces variation between shifts and makes first-off inspection more predictable.
Common Mistakes and How to Avoid Them
- Using half-angle as the full angle: Enter included point angle (e.g., 118°), not 59°.
- Ignoring units: Keep diameter and output in the same base unit, then convert once.
- Assuming all drills are 118°: Verify actual tool geometry from manufacturer data.
- Forgetting worn or reground tools: Reground points can change effective geometry.
- Not separating full diameter from tip depth: Drawings often care about cylindrical depth, not apex depth.
Best Practices for Reliable Depth Results
Use consistent tool libraries with verified point angle data. Include tip compensation rules in your CNC programming standards. For critical parts, validate depth with sectioning or bore measurement methods that confirm true full-diameter depth. When possible, assign separate values in setup documentation for “programmed depth” and “required cylindrical depth” so everyone on the line reads the same intent.
In high-volume work, small improvements in hole-depth consistency can significantly reduce rework. Tip length calculation is a simple control point that often pays back immediately in process stability.
FAQ: Drill Tip Length Calculator
Is drill tip length the same as flute length?
No. Flute length is the cutting channel length along the body of the drill. Tip length is only the conical end height.
Can I use this for spot drills and center drills?
Yes, if you know the effective point angle and diameter at the reference location. The same cone geometry applies.
Why is my measured value slightly different from the calculator?
Manufacturing tolerances, split-point geometry, wear, and regrinding can change the exact shape from ideal math.
What angle should I choose if I am not sure?
Use the tool’s published point angle from your tool list or manufacturer catalog. Do not assume.
Does coolant or feed rate affect tip length?
No. Tip length is geometric. Coolant and feeds affect cutting performance and finish, not the theoretical cone height.
Conclusion
A drill tip length calculator is a fast, practical way to improve depth accuracy in drilling operations. By entering diameter and point angle, you can instantly determine the cone height and apply correct depth compensation for blind holes, tapping prep, and quality-critical features. Keep this page as a shop reference whenever you change tool diameters or point geometries.