mm
Indicative value for a cutting tap.YG-1 ↗Machining calculator · Metric threads
Metric tap drill size calculator
Choose an ISO metric thread to obtain the theoretical D − P diameter and a common drill size before cutting-tap operations.
Created v1.0
By Thibaut Grzelak, Mechanical Analysis Engineer
01
Calculation inputs
Covered processCutting tapForming taps require a different pilot-hole diameter.
02
Diagram
d₀ ≈ D − P
Value guide
D and P define the thread. d₀ is a starting approximation before selecting the common drill size.
03
Results
mm
d₀ ≈ D − PCheck material, tolerance, depth and the tap manufacturer’s data sheet.
View calculation detailsFormula, worked example and interpretationOpen ↓
Geometric approximation
d₀ ≈ D − P
M10 × 1.5: 10 − 1.5 = 8.5 mm
What the result means
The formula gives a starting value. The displayed drill comes from a common-practice table and may be rounded slightly.
Reference table
Metric tap drill chart M1 to M48
Filter common coarse and fine pitches, then send any row to the calculator.
Scroll the table to see more threads.
| Thread | Common drill | Theoretical D − P | Series | Action |
|---|---|---|---|---|
| M1 × 0.25 | — | 0.75 mm | Coarse | |
| M1.1 × 0.25 | — | 0.85 mm | Coarse | |
| M1.2 × 0.25 | — | 0.95 mm | Coarse | |
| M1.4 × 0.3 | — | 1.1 mm | Coarse | |
| M1.6 × 0.35 | 1.25 mmYG-1 ↗ | 1.25 mm | Coarse | |
| M1.8 × 0.35 | 1.45 mmYG-1 ↗ | 1.45 mm | Coarse | |
| M2 × 0.4 | 1.6 mmYG-1 ↗ | 1.6 mm | Coarse | |
| M2.2 × 0.45 | 1.75 mmYG-1 ↗ | 1.75 mm | Coarse | |
| M2.5 × 0.45 | 2.05 mmYG-1 ↗ | 2.05 mm | Coarse | |
| M3 × 0.5 | 2.5 mmYG-1 ↗ | 2.5 mm | Coarse | |
| M3.5 × 0.6 | 2.9 mmYG-1 ↗ | 2.9 mm | Coarse | |
| M4 × 0.7 | 3.3 mmYG-1 ↗ | 3.3 mm | Coarse | |
| M4.5 × 0.75 | 3.7 mmYG-1 ↗ | 3.75 mm | Coarse | |
| M5 × 0.8 | 4.2 mmYG-1 ↗ | 4.2 mm | Coarse | |
| M6 × 1 | 5 mmYG-1 ↗ | 5 mm | Coarse | |
| M7 × 1 | 6 mmYG-1 ↗ | 6 mm | Coarse | |
| M8 × 1.25 | 6.8 mmUK Drills ↗ | 6.75 mm | Coarse | |
| M9 × 1.25 | — | 7.75 mm | Coarse | |
| M10 × 1.5 | 8.5 mmYG-1 ↗ | 8.5 mm | Coarse | |
| M11 × 1.5 | — | 9.5 mm | Coarse | |
| M12 × 1.75 | 10.2 mmYG-1 ↗ | 10.25 mm | Coarse | |
| M14 × 2 | 12 mmYG-1 ↗ | 12 mm | Coarse | |
| M16 × 2 | 14 mmYG-1 ↗ | 14 mm | Coarse | |
| M18 × 2.5 | 15.5 mmYG-1 ↗ | 15.5 mm | Coarse | |
| M20 × 2.5 | 17.5 mmYG-1 ↗ | 17.5 mm | Coarse | |
| M22 × 2.5 | 19.5 mmYG-1 ↗ | 19.5 mm | Coarse | |
| M24 × 3 | 21 mmYG-1 ↗ | 21 mm | Coarse | |
| M27 × 3 | 24 mmYG-1 ↗ | 24 mm | Coarse | |
| M30 × 3.5 | 26.5 mmYG-1 ↗ | 26.5 mm | Coarse | |
| M33 × 3.5 | 29.5 mmYG-1 ↗ | 29.5 mm | Coarse | |
| M36 × 4 | 32 mmYG-1 ↗ | 32 mm | Coarse | |
| M39 × 4 | 35 mmYG-1 ↗ | 35 mm | Coarse | |
| M42 × 4.5 | — | 37.5 mm | Coarse | |
| M45 × 4.5 | — | 40.5 mm | Coarse | |
| M48 × 5 | — | 43 mm | Coarse | |
| M2 × 0.25 | — | 1.75 mm | Fine | |
| M2.5 × 0.35 | — | 2.15 mm | Fine | |
| M3 × 0.35 | — | 2.65 mm | Fine | |
| M3.5 × 0.35 | — | 3.15 mm | Fine | |
| M4 × 0.5 | — | 3.5 mm | Fine | |
| M4.5 × 0.5 | — | 4 mm | Fine | |
| M5 × 0.5 | — | 4.5 mm | Fine | |
| M5 × 0.75 | — | 4.25 mm | Fine | |
| M6 × 0.5 | — | 5.5 mm | Fine | |
| M6 × 0.75 | — | 5.25 mm | Fine | |
| M7 × 0.75 | — | 6.25 mm | Fine | |
| M8 × 0.5 | — | 7.5 mm | Fine | |
| M8 × 0.75 | — | 7.25 mm | Fine | |
| M8 × 1 | 7 mmYG-1 ↗ | 7 mm | Fine | |
| M9 × 0.75 | — | 8.25 mm | Fine | |
| M9 × 1 | — | 8 mm | Fine | |
| M10 × 0.75 | — | 9.25 mm | Fine | |
| M10 × 1 | — | 9 mm | Fine | |
| M10 × 1.25 | 8.8 mmUK Drills ↗ | 8.75 mm | Fine | |
| M11 × 1 | — | 10 mm | Fine | |
| M12 × 1 | — | 11 mm | Fine | |
| M12 × 1.25 | 10.8 mmYG-1 ↗ | 10.75 mm | Fine | |
| M12 × 1.5 | 10.5 mmUK Drills ↗ | 10.5 mm | Fine | |
| M14 × 1 | — | 13 mm | Fine | |
| M14 × 1.25 | — | 12.75 mm | Fine | |
| M14 × 1.5 | 12.5 mmYG-1 ↗ | 12.5 mm | Fine | |
| M16 × 1 | — | 15 mm | Fine | |
| M16 × 1.5 | 14.5 mmYG-1 ↗ | 14.5 mm | Fine | |
| M18 × 1 | — | 17 mm | Fine | |
| M18 × 1.5 | 16.5 mmYG-1 ↗ | 16.5 mm | Fine | |
| M18 × 2 | — | 16 mm | Fine | |
| M20 × 1 | — | 19 mm | Fine | |
| M20 × 1.5 | 18.5 mmYG-1 ↗ | 18.5 mm | Fine | |
| M20 × 2 | — | 18 mm | Fine | |
| M22 × 1 | — | 21 mm | Fine | |
| M22 × 1.5 | 20.5 mmYG-1 ↗ | 20.5 mm | Fine | |
| M22 × 2 | — | 20 mm | Fine | |
| M24 × 1.5 | — | 22.5 mm | Fine | |
| M24 × 2 | 22 mmYG-1 ↗ | 22 mm | Fine | |
| M27 × 1.5 | — | 25.5 mm | Fine | |
| M27 × 2 | 25 mmYG-1 ↗ | 25 mm | Fine | |
| M30 × 1.5 | — | 28.5 mm | Fine | |
| M30 × 2 | 28 mmYG-1 ↗ | 28 mm | Fine | |
| M30 × 3 | — | 27 mm | Fine | |
| M33 × 1.5 | — | 31.5 mm | Fine | |
| M33 × 2 | 31 mmYG-1 ↗ | 31 mm | Fine | |
| M33 × 3 | — | 30 mm | Fine | |
| M36 × 1.5 | — | 34.5 mm | Fine | |
| M36 × 2 | — | 34 mm | Fine | |
| M36 × 3 | 33 mmYG-1 ↗ | 33 mm | Fine | |
| M39 × 1.5 | — | 37.5 mm | Fine | |
| M39 × 2 | — | 37 mm | Fine | |
| M39 × 3 | 36 mmYG-1 ↗ | 36 mm | Fine | |
| M42 × 1.5 | — | 40.5 mm | Fine | |
| M42 × 2 | — | 40 mm | Fine | |
| M42 × 3 | — | 39 mm | Fine | |
| M42 × 4 | — | 38 mm | Fine | |
| M45 × 1.5 | — | 43.5 mm | Fine | |
| M45 × 2 | — | 43 mm | Fine | |
| M45 × 3 | — | 42 mm | Fine | |
| M45 × 4 | — | 41 mm | Fine | |
| M48 × 1.5 | — | 46.5 mm | Fine | |
| M48 × 2 | — | 46 mm | Fine | |
| M48 × 3 | — | 45 mm | Fine | |
| M48 × 4 | — | 44 mm | Fine |
No thread matches this filter.
— Drill size not verified: consult the manufacturer.
Method
How to select the pilot hole
- Identify the thread’s nominal diameter and pitch.
- Use D − P as a quick check, not as a normative dimension.
- Select the common drill, then check the tap data sheet and work material.
Limits
When the value must be adjusted
The actual diameter depends on tolerance class, work material, target thread percentage, depth and tap type. A forming tap requires a larger hole than a cutting tap.
Technical traceability
Standards and references used
Diameter/pitch designations follow ISO metric threads. Drill sizes are common manufacturer values, separate from standardized basic thread dimensions.
M8 × 1.25: D − P gives 6.75 mm; UK Drills lists 6.8 mm and YG-1 6.7 mm. Follow the data sheet for your tap.