Drill Point Length Table — 118°, 120°, 135° & 140°
Calculated drill-point allowances by diameter and included angle, with cone-depth factors and a clear distinction between tip and full-diameter depth.
Updated September 6, 2026
Use this calculated table when a hole drawing gives full-diameter depth but your setup measures travel to the drill tip. Each entry is the axial length of an ideal conical point, h = D/[2 tan(θ/2)]. Add it to the cylindrical depth to obtain the corresponding ideal tip depth. Diameter and allowance must use the same unit. The first table uses millimetres; the dimensionless factor table works in either inches or millimetres.
The entries are computed from the stated geometry, not copied from a manufacturer’s dimensional drawing and not measured values for a particular drill. A split point or reground tool may not end in the ideal profile. Treat the table as a geometry reference, check the actual tool, and keep tapping lead, machine offsets, pecking, and breakthrough allowances separate. The angle headings describe included point angle; using that full angle inside the tangent would give the wrong result.
Ideal point allowance by drill diameter
| Drill Ø (mm) | 118° h (mm) | 120° h (mm) | 135° h (mm) | 140° h (mm) |
|---|---|---|---|---|
| 1 | 0.3004 | 0.2887 | 0.2071 | 0.1820 |
| 2 | 0.6009 | 0.5774 | 0.4142 | 0.3640 |
| 3 | 0.9013 | 0.8660 | 0.6213 | 0.5460 |
| 4 | 1.2017 | 1.1547 | 0.8284 | 0.7279 |
| 5 | 1.5022 | 1.4434 | 1.0355 | 0.9099 |
| 6 | 1.8026 | 1.7321 | 1.2426 | 1.0919 |
| 8 | 2.4034 | 2.3094 | 1.6569 | 1.4559 |
| 10 | 3.0043 | 2.8868 | 2.0711 | 1.8199 |
| 12 | 3.6052 | 3.4641 | 2.4853 | 2.1838 |
| 16 | 4.8069 | 4.6188 | 3.3137 | 2.9118 |
| 20 | 6.0086 | 5.7735 | 4.1421 | 3.6397 |
| 25 | 7.5108 | 7.2169 | 5.1777 | 4.5496 |
Rounded to four decimals for lookup. The calculator retains full precision; these are cone allowances, not recommended machine settings.
Multiply any diameter by the point factor
| Included angle | h / D | h for Ø10 mm |
|---|---|---|
| 90° | 0.500000 | 5.0000 |
| 118° | 0.300430 | 3.0043 |
| 120° | 0.288675 | 2.8868 |
| 135° | 0.207107 | 2.0711 |
| 140° | 0.181985 | 1.8199 |
Multiply D by h/D in the same length unit. Presets are geometry examples, not material or tool-selection advice.
Sources & Further Reading
- Independent right-triangle derivation: tan(θ/2) = (D/2)/h. All numeric cells are computed from that identity.
- Harvey Performance Company, Spot Drilling: The First Step to Precision Drilling (updated 2023), point-angle convention — https://www.harveyperformance.com/in-the-loupe/choosing-spot-drill/
Frequently Asked Questions
Is the 0.3-times-diameter drill-point rule exact?
It is a convenient approximation for an ideal 118-degree point. The more precise factor is about 0.300430. Other point angles use different factors, so a blanket 0.3D rule can misstate the bottom geometry.
Can the factor table be used with inch drills?
Yes. The ratio h/D is dimensionless. Multiply an inch diameter by the listed factor to get inches of ideal point length. The diameter-by-angle table above is explicitly in millimetres.
Do these allowances include extra clearance beyond the workpiece?
No. They are only the geometric length between the drill’s full-diameter shoulder and its ideal tip. Any additional clearance depends on the operation, tool, fixture, and machining instructions.
Try the Calculators
Drill Point Length Table — 118°, 120°, 135° & 140° — reuven.tools/reference/drill-point-lengths — verified against: Independent right-triangle derivation: tan(θ/2) = (D/2)/h. All numeric cells are computed from that identity.; Harvey Performance Company, Spot Drilling: The First Step to Precision Drilling (updated 2023), point-angle convention — https://www.harveyperformance.com/in-the-loupe/choosing-spot-drill/