Interactive selector
Find the Correct Tap Drill Size
Choose a thread and target engagement. The tool matches the calculated hole to the nearest enabled standard drill.
Without JavaScript, use the 75% reference table immediately below. The interactive result is a general-purpose starting point for 60° cutting taps, not a finished-thread acceptance limit.
75% starting point
Tap Drill Size Reference Table
Common cutting-tap recommendations calculated at 75% target engagement and matched to the nearest listed drill.
Search by thread designation, pitch, TPI, or drill size. Filter by system or series. Select a row in the calculator above for adjustable results.
More table filters and actions
No supported thread or drill matches these filters. Clear filters or choose another thread series.
Scroll horizontally to view additional columns and vertically to view additional rows. Column headers remain visible while scrolling.
| Thread | Calculated recommendation | Standard drill match | Copy | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Pitch / TPI | Target | Recommended drill | ||||||||
| #0-80 UNC | UNC | 0.0600 in | 80 TPI | 75% | 0.0478 in | 1.2 mm | 0.0472 | 1.20 | 78.6% | |
| #1-64 UNC | UNC | 0.0730 in | 64 TPI | 75% | 0.0578 in | 1.5 mm | 0.0591 | 1.50 | 68.7% | |
| #2-56 UNC | UNC | 0.0860 in | 56 TPI | 75% | 0.0686 in | #50 | 0.0700 | 1.78 | 69.0% | |
| #3-48 UNC | UNC | 0.0990 in | 48 TPI | 75% | 0.0787 in | 2 mm | 0.0787 | 2.00 | 74.9% | |
| #4-40 UNC | UNC | 0.1120 in | 40 TPI | 75% | 0.0876 in | 2.2 mm | 0.0866 | 2.20 | 78.2% | |
| #5-40 UNC | UNC | 0.1250 in | 40 TPI | 75% | 0.1006 in | #38 | 0.1015 | 2.58 | 72.4% | |
| #6-32 UNC | UNC | 0.1380 in | 32 TPI | 75% | 0.1076 in | #36 | 0.1065 | 2.71 | 77.6% | |
| #8-32 UNC | UNC | 0.1640 in | 32 TPI | 75% | 0.1336 in | 3.4 mm | 0.1339 | 3.40 | 74.3% | |
| #10-24 UNC | UNC | 0.1900 in | 24 TPI | 75% | 0.1494 in | #25 | 0.1495 | 3.80 | 74.8% | |
| #12-24 UNC | UNC | 0.2160 in | 24 TPI | 75% | 0.1754 in | #16 | 0.1770 | 4.50 | 72.1% | |
| 1/4-20 UNC | UNC | 0.2500 in | 20 TPI | 75% | 0.2013 in | #7 | 0.2010 | 5.11 | 75.4% | |
| 5/16-18 UNC | UNC | 0.3125 in | 18 TPI | 75% | 0.2584 in | F | 0.2570 | 6.53 | 76.9% | |
| 3/8-16 UNC | UNC | 0.3750 in | 16 TPI | 75% | 0.3141 in | 8 mm | 0.3150 | 8.00 | 74.0% | |
| 7/16-14 UNC | UNC | 0.4375 in | 14 TPI | 75% | 0.3679 in | U | 0.3680 | 9.35 | 74.9% | |
| 1/2-13 UNC | UNC | 0.5000 in | 13 TPI | 75% | 0.4251 in | 10.8 mm | 0.4252 | 10.80 | 74.9% | |
| 9/16-12 UNC | UNC | 0.5625 in | 12 TPI | 75% | 0.4813 in | 12.2 mm | 0.4803 | 12.20 | 75.9% | |
| 5/8-11 UNC | UNC | 0.6250 in | 11 TPI | 75% | 0.5364 in | 13.6 mm | 0.5354 | 13.60 | 75.8% | |
| 3/4-10 UNC | UNC | 0.7500 in | 10 TPI | 75% | 0.6526 in | 16.6 mm | 0.6535 | 16.60 | 74.3% | |
| 7/8-9 UNC | UNC | 0.8750 in | 9 TPI | 75% | 0.7668 in | 19.5 mm | 0.7677 | 19.50 | 74.3% | |
| 1-8 UNC | UNC | 1.0000 in | 8 TPI | 75% | 0.8782 in | 7/8 in | 0.8750 | 22.22 | 77.0% | |
| #0-80 UNF | UNF | 0.0600 in | 80 TPI | 75% | 0.0478 in | 1.2 mm | 0.0472 | 1.20 | 78.6% | |
| #1-72 UNF | UNF | 0.0730 in | 72 TPI | 75% | 0.0595 in | #53 | 0.0595 | 1.51 | 74.8% | |
| #2-64 UNF | UNF | 0.0860 in | 64 TPI | 75% | 0.0708 in | 1.8 mm | 0.0709 | 1.80 | 74.6% | |
| #3-56 UNF | UNF | 0.0990 in | 56 TPI | 75% | 0.0816 in | #45 | 0.0820 | 2.08 | 73.3% | |
| #4-48 UNF | UNF | 0.1120 in | 48 TPI | 75% | 0.0917 in | 2.3 mm | 0.0906 | 2.30 | 79.3% | |
| #5-44 UNF | UNF | 0.1250 in | 44 TPI | 75% | 0.1029 in | 2.6 mm | 0.1024 | 2.60 | 76.7% | |
| #6-40 UNF | UNF | 0.1380 in | 40 TPI | 75% | 0.1136 in | 2.9 mm | 0.1142 | 2.90 | 73.4% | |
| #8-36 UNF | UNF | 0.1640 in | 36 TPI | 75% | 0.1369 in | 3.5 mm | 0.1378 | 3.50 | 72.6% | |
| #10-32 UNF | UNF | 0.1900 in | 32 TPI | 75% | 0.1596 in | #21 | 0.1590 | 4.04 | 76.4% | |
| #12-28 UNF | UNF | 0.2160 in | 28 TPI | 75% | 0.1812 in | 4.6 mm | 0.1811 | 4.60 | 75.2% | |
| 1/4-28 UNF | UNF | 0.2500 in | 28 TPI | 75% | 0.2152 in | 5.5 mm | 0.2165 | 5.50 | 72.1% | |
| 5/16-24 UNF | UNF | 0.3125 in | 24 TPI | 75% | 0.2719 in | I | 0.2720 | 6.91 | 74.8% | |
| 3/8-24 UNF | UNF | 0.3750 in | 24 TPI | 75% | 0.3344 in | 8.5 mm | 0.3346 | 8.50 | 74.6% | |
| 7/16-20 UNF | UNF | 0.4375 in | 20 TPI | 75% | 0.3888 in | 9.9 mm | 0.3898 | 9.90 | 73.5% | |
| 1/2-20 UNF | UNF | 0.5000 in | 20 TPI | 75% | 0.4513 in | 11.5 mm | 0.4528 | 11.50 | 72.7% | |
| 9/16-18 UNF | UNF | 0.5625 in | 18 TPI | 75% | 0.5084 in | 12.9 mm | 0.5079 | 12.90 | 75.7% | |
| 5/8-18 UNF | UNF | 0.6250 in | 18 TPI | 75% | 0.5709 in | 14.5 mm | 0.5709 | 14.50 | 75.0% | |
| 3/4-16 UNF | UNF | 0.7500 in | 16 TPI | 75% | 0.6891 in | 17.5 mm | 0.6890 | 17.50 | 75.2% | |
| 7/8-14 UNF | UNF | 0.8750 in | 14 TPI | 75% | 0.8054 in | 13/16 in | 0.8125 | 20.64 | 67.4% | |
| 1-12 UNF | UNF | 1.0000 in | 12 TPI | 75% | 0.9188 in | 59/64 in | 0.9219 | 23.42 | 72.2% | |
| M1.6 × 0.35 | Metric coarse | 1.6 mm | 0.35 mm | 75% | 0.0496 in | 1.3 mm | 0.0512 | 1.30 | 66.0% | |
| M2 × 0.4 | Metric coarse | 2 mm | 0.4 mm | 75% | 0.0634 in | #52 | 0.0635 | 1.61 | 74.5% | |
| M2.5 × 0.45 | Metric coarse | 2.5 mm | 0.45 mm | 75% | 0.0812 in | #46 | 0.0810 | 2.06 | 75.7% | |
| M3 × 0.5 | Metric coarse | 3 mm | 0.5 mm | 75% | 0.0989 in | 2.5 mm | 0.0984 | 2.50 | 77.0% | |
| M3.5 × 0.6 | Metric coarse | 3.5 mm | 0.6 mm | 75% | 0.1148 in | 2.9 mm | 0.1142 | 2.90 | 77.0% | |
| M4 × 0.7 | Metric coarse | 4 mm | 0.7 mm | 75% | 0.1306 in | 3.3 mm | 0.1299 | 3.30 | 77.0% | |
| M5 × 0.8 | Metric coarse | 5 mm | 0.8 mm | 75% | 0.1662 in | #19 | 0.1660 | 4.22 | 75.4% | |
| M6 × 1 | Metric coarse | 6 mm | 1 mm | 75% | 0.1979 in | 5 mm | 0.1969 | 5.00 | 77.0% | |
| M8 × 1.25 | Metric coarse | 8 mm | 1.25 mm | 75% | 0.2670 in | 6.8 mm | 0.2677 | 6.80 | 73.9% | |
| M10 × 1.5 | Metric coarse | 10 mm | 1.5 mm | 75% | 0.3362 in | 8.5 mm | 0.3346 | 8.50 | 77.0% | |
| M12 × 1.75 | Metric coarse | 12 mm | 1.75 mm | 75% | 0.4053 in | 10.3 mm | 0.4055 | 10.30 | 74.8% | |
| M14 × 2 | Metric coarse | 14 mm | 2 mm | 75% | 0.4745 in | 12.1 mm | 0.4764 | 12.10 | 73.1% | |
| M16 × 2 | Metric coarse | 16 mm | 2 mm | 75% | 0.5532 in | 14.1 mm | 0.5551 | 14.10 | 73.1% | |
| M18 × 2.5 | Metric coarse | 18 mm | 2.5 mm | 75% | 0.6128 in | 15.6 mm | 0.6142 | 15.60 | 73.9% | |
| M20 × 2.5 | Metric coarse | 20 mm | 2.5 mm | 75% | 0.6915 in | 17.6 mm | 0.6929 | 17.60 | 73.9% | |
| M22 × 2.5 | Metric coarse | 22 mm | 2.5 mm | 75% | 0.7703 in | 19.6 mm | 0.7717 | 19.60 | 73.9% | |
| M24 × 3 | Metric coarse | 24 mm | 3 mm | 75% | 0.8298 in | 53/64 in | 0.8281 | 21.03 | 76.1% | |
| M27 × 3 | Metric coarse | 27 mm | 3 mm | 75% | 0.9479 in | 61/64 in | 0.9531 | 24.21 | 71.6% | |
| M30 × 3.5 | Metric coarse | 30 mm | 3.5 mm | 75% | 1.0469 in | 1 in | 1.0000 | 25.40 | 101.2% | |
| M36 × 4 | Metric coarse | 36 mm | 4 mm | 75% | 1.2639 in | 1 in | 1.0000 | 25.40 | 204.0% | |
| M4 × 0.5 | Metric fine | 4 mm | 0.5 mm | 75% | 0.1383 in | 3.5 mm | 0.1378 | 3.50 | 77.0% | |
| M5 × 0.5 | Metric fine | 5 mm | 0.5 mm | 75% | 0.1777 in | 4.5 mm | 0.1772 | 4.50 | 77.0% | |
| M6 × 0.75 | Metric fine | 6 mm | 0.75 mm | 75% | 0.2075 in | 5.3 mm | 0.2087 | 5.30 | 71.9% | |
| M8 × 1 | Metric fine | 8 mm | 1 mm | 75% | 0.2766 in | J | 0.2770 | 7.04 | 74.2% | |
| M10 × 1 | Metric fine | 10 mm | 1 mm | 75% | 0.3553 in | 9 mm | 0.3543 | 9.00 | 77.0% | |
| M10 × 1.25 | Metric fine | 10 mm | 1.25 mm | 75% | 0.3458 in | 8.8 mm | 0.3465 | 8.80 | 73.9% | |
| M12 × 1.25 | Metric fine | 12 mm | 1.25 mm | 75% | 0.4245 in | 10.8 mm | 0.4252 | 10.80 | 73.9% | |
| M12 × 1.5 | Metric fine | 12 mm | 1.5 mm | 75% | 0.4149 in | 10.5 mm | 0.4134 | 10.50 | 77.0% | |
| M14 × 1.5 | Metric fine | 14 mm | 1.5 mm | 75% | 0.4936 in | 12.5 mm | 0.4921 | 12.50 | 77.0% | |
| M16 × 1.5 | Metric fine | 16 mm | 1.5 mm | 75% | 0.5724 in | 14.5 mm | 0.5709 | 14.50 | 77.0% | |
| M18 × 1.5 | Metric fine | 18 mm | 1.5 mm | 75% | 0.6511 in | 16.5 mm | 0.6496 | 16.50 | 77.0% | |
| M20 × 1.5 | Metric fine | 20 mm | 1.5 mm | 75% | 0.7299 in | 18.5 mm | 0.7283 | 18.50 | 77.0% | |
| M24 × 2 | Metric fine | 24 mm | 2 mm | 75% | 0.8682 in | 7/8 in | 0.8750 | 22.22 | 68.3% | |
| M30 × 2 | Metric fine | 30 mm | 2 mm | 75% | 1.1044 in | 1 in | 1.0000 | 25.40 | 177.1% | |
| M36 × 3 | Metric fine | 36 mm | 3 mm | 75% | 1.3023 in | 1 in | 1.0000 | 25.40 | 272.0% | |
These are calculated starting points, not finished internal-thread tolerance limits. A nominal 75% target may map to a standard drill that produces a slightly different actual engagement.
How Tap Drill Size Is Calculated
For common 60° Unified and ISO metric threads, a practical tap-drill estimate starts with the nominal major diameter, thread pitch, and a target percentage of thread engagement. The result is then matched to an available standard drill.
E is entered as a whole-number percentage, such as 75.
P is pitch in millimeters.
- Ideal hole
- The unrounded calculated diameter for the selected engagement.
- Recommended drill
- The enabled standard drill with the smallest absolute diameter difference; a larger drill wins an exact tie.
- Actual engagement
- The engagement recalculated from the selected drill’s canonical diameter.
Worked Tap Drill Examples
1/4-20 UNC at 75%
Assumptions: 0.2500 in nominal diameter, 20 TPI, general-purpose cutting tap.
Dhole = 0.2500 − (0.01299 × 75 ÷ 20) = 0.2013 in.
The nearest standard drill in the full inventory is a #7 drill at 0.2010 in, producing approximately 75.5% engagement.
Sanity check: the selected drill is slightly smaller than the ideal hole, so actual engagement is slightly higher than 75%.
M8 × 1.25 at 75%
Assumptions: 8 mm nominal diameter, 1.25 mm pitch, general-purpose cutting tap.
Dhole = 8 − (0.01299 × 75 × 1.25) = 6.782 mm.
The nearest common metric drill is 6.8 mm, producing approximately 73.9% engagement.
Sanity check: the selected drill is slightly larger than the ideal hole, so actual engagement is slightly lower than 75%.
Choosing the Right Tap Drill in Practice
75% is a starting point
- Higher engagement generally increases tapping torque and does not always add proportional thread strength.
- A slightly larger hole can improve tool life and chip evacuation in difficult materials.
- Use the adjacent-drill output to see the tradeoff before changing sizes.
Cutting taps vs forming taps
- Cutting taps remove material and are the intended use of this page.
- Forming or roll taps displace material and normally require a larger, tightly controlled pre-hole.
- Use the specific forming-tap manufacturer’s chart rather than this calculator.
Check the process
- Account for drill tolerance, runout, material springback, blind-hole depth, coolant, machine rigidity, and tap geometry.
- Confirm the thread class and finished minor diameter with the applicable standard and inspection method.
- For safety-critical work, qualify the process with controlled trials.
Common tap drill mistakes
- Using a clearance-hole chart instead of a tap-drill chart.
- Mixing UNC and UNF pitches for the same nominal diameter.
- Entering pitch as TPI or assuming every metric thread uses coarse pitch.
- Rounding the ideal diameter before finding the nearest drill.
- Using cutting-tap data for a forming tap.
- Treating approximate engagement as a finished-thread acceptance measurement.
Standards, Method, and Data Rights
Common UNC, UNF, ISO metric coarse, and selected metric fine 60° cutting-tap applications.
The page uses independently calculated hole diameters and an internally maintained drill inventory. Standards are used only to verify thread forms, naming, and designation scope; the tap-drill results are independently calculated and protected standards tables are not reproduced.
- ASME B1.1-2024 — Unified Inch Screw ThreadsCurrent Unified thread-form, series, and designation scope. Copyrighted standard; cited for scope and verification, not reproduced.
- ISO 68-1:2023 — Metric Screw Thread Basic and Design ProfilesCurrent ISO metric 60° basic and design profile basis. Copyrighted standard; this page publishes independently calculated results.
- ISO 261:1998 and ISO 262:2023General metric thread plan and selected commercial diameter-pitch combinations. Protected tables are not reproduced or downloadable.
- Turn2Engineering Drill Bit Size ChartCanonical numbered, lettered, fractional, metric, and decimal drill-size reference used for nearest-size matching.
Dataset and Source-Check Details
- Dataset label
- tap-drill-data-1.0.0
- Calculated fields
- Ideal hole diameter, nearest drill, diameter difference, approximate engagement
- Default condition
- 75% target engagement
- Supported engagement
- 50%–85%
- Download status
- Full standards-derived CSV disabled pending rights review
- Publisher
- Turn2Engineering
Tap Drill Chart FAQs
At the default 75% cutting-tap estimate, the calculated hole is about 0.2013 in and the nearest standard match is a #7 drill at 0.2010 in.
Charts may assume different engagement percentages, drill inventories, rounding rules, materials, tap styles, or cutting versus forming processes.
No. It is a common general-purpose starting point, while higher engagement can sharply increase tapping torque without providing proportional strength improvement.
No. Forming taps need manufacturer-specific pre-hole sizes that are generally larger and more tightly controlled than cutting-tap holes.
No. A tap drill leaves material for internal threads, while a clearance hole lets the fastener body pass through.
Use the Result as a Machining Starting Point
Select the exact thread and engagement needed, confirm the recommended standard drill, then review the actual engagement and adjacent sizes. Before production, verify the tap manufacturer’s guidance, material behavior, thread tolerance, and inspection requirements.
- Browse all engineering charts and tables
Continue to related interactive references on Turn2Engineering.