Tap Drill Chart – UNC, UNF & Metric

Look up the drill size to use before tapping common UNC, UNF, metric coarse, and metric fine threads.

The complete tap drill chart is available below without JavaScript. JavaScript adds search, filtering, matched-row answers, sharing, and the optional percent-thread calculator.

Tap Drill Size Chart

Find the thread size, then use the drill shown beside it. Search by thread, tap size, or drill designation.

#10-32 UNF #21 0.1590 in · 4.04 mm

1/4-20 UNC #7 0.2010 in · 5.11 mm

1/4-28 UNF #3 0.2130 in · 5.41 mm

3/8-16 UNC 5/16 in 0.3125 in · 7.94 mm

M6 × 1 5 mm 0.1969 in · 5.00 mm

M8 × 1.25 6.8 mm 0.2677 in · 6.80 mm

Use your browser’s find feature or browse the chart below. Example: 1/4-20 UNC uses a #7 drill.

Standard cutting-tap drill starting sizes for common Unified inch and ISO metric threads.
	Tap drill
#0-80 UNC	3/64 in	0.0469	1.19
#1-64 UNC	#53	0.0595	1.51
#2-56 UNC	#50	0.0700	1.78
#3-48 UNC	#47	0.0785	1.99
#4-40 UNC	#43	0.0890	2.26
#5-40 UNC	#38	0.1015	2.58
#6-32 UNC	#36	0.1065	2.71
#8-32 UNC	#29	0.1360	3.45
#10-24 UNC	#25	0.1495	3.80
#12-24 UNC	#16	0.1770	4.50
1/4-20 UNC	#7	0.2010	5.11
5/16-18 UNC	F	0.2570	6.53
3/8-16 UNC	5/16 in	0.3125	7.94
7/16-14 UNC	U	0.3680	9.35
1/2-13 UNC	27/64 in	0.4219	10.72
9/16-12 UNC	31/64 in	0.4844	12.30
5/8-11 UNC	17/32 in	0.5312	13.49
3/4-10 UNC	21/32 in	0.6562	16.67
7/8-9 UNC	49/64 in	0.7656	19.45
1-8 UNC	7/8 in	0.8750	22.22
#0-80 UNF	3/64 in	0.0469	1.19
#1-72 UNF	#53	0.0595	1.51
#2-64 UNF	#50	0.0700	1.78
#3-56 UNF	#45	0.0820	2.08
#4-48 UNF	#42	0.0935	2.37
#5-44 UNF	#37	0.1040	2.64
#6-40 UNF	#33	0.1130	2.87
#8-36 UNF	#29	0.1360	3.45
#10-32 UNF	#21	0.1590	4.04
#12-28 UNF	#14	0.1820	4.62
1/4-28 UNF	#3	0.2130	5.41
5/16-24 UNF	I	0.2720	6.91
3/8-24 UNF	Q	0.3320	8.43
7/16-20 UNF	25/64 in	0.3906	9.92
1/2-20 UNF	29/64 in	0.4531	11.51
9/16-18 UNF	33/64 in	0.5156	13.10
5/8-18 UNF	37/64 in	0.5781	14.68
3/4-16 UNF	11/16 in	0.6875	17.46
7/8-14 UNF	13/16 in	0.8125	20.64
1-12 UNF	59/64 in	0.9219	23.42
M1.6 × 0.35	1.25 mm	0.0492	1.25
M2 × 0.4	1.6 mm	0.0630	1.60
M2.5 × 0.45	2.05 mm	0.0807	2.05
M3 × 0.5	2.5 mm	0.0984	2.50
M3.5 × 0.6	2.9 mm	0.1142	2.90
M4 × 0.7	3.3 mm	0.1299	3.30
M5 × 0.8	4.2 mm	0.1654	4.20
M6 × 1	5 mm	0.1969	5.00
M8 × 1.25	6.8 mm	0.2677	6.80
M10 × 1.5	8.5 mm	0.3346	8.50
M12 × 1.75	10.2 mm	0.4016	10.20
M14 × 2	12 mm	0.4724	12.00
M16 × 2	14 mm	0.5512	14.00
M18 × 2.5	15.5 mm	0.6102	15.50
M20 × 2.5	17.5 mm	0.6890	17.50
M22 × 2.5	19.5 mm	0.7677	19.50
M24 × 3	21 mm	0.8268	21.00
M27 × 3	24 mm	0.9449	24.00
M30 × 3.5	26.5 mm	1.0433	26.50
M36 × 4	32 mm	1.2598	32.00
M4 × 0.5	3.5 mm	0.1378	3.50
M5 × 0.5	4.5 mm	0.1772	4.50
M6 × 0.75	5.25 mm	0.2067	5.25
M8 × 1	7 mm	0.2756	7.00
M10 × 1	9 mm	0.3543	9.00
M10 × 1.25	8.8 mm	0.3465	8.80
M12 × 1.25	10.8 mm	0.4252	10.80
M12 × 1.5	10.5 mm	0.4134	10.50
M14 × 1.5	12.5 mm	0.4921	12.50
M16 × 1.5	14.5 mm	0.5709	14.50
M18 × 1.5	16.5 mm	0.6496	16.50
M20 × 1.5	18.5 mm	0.7283	18.50
M24 × 2	22 mm	0.8661	22.00
M30 × 2	28 mm	1.1024	28.00
M36 × 3	33 mm	1.2992	33.00

Cutting taps only. These are practical starting sizes. For production work, difficult materials, special tolerances, or a specific tool geometry, verify the tap manufacturer’s recommended pre-hole.

Printed scope: common UNC, UNF, metric coarse, and selected metric fine cutting-tap starting sizes.

Print, share, or reset the chart

Tap Drill Calculator for a Different Percent Thread

Most visitors only need the chart above. Use this when you intentionally want to compare the standard drill with another theoretical thread-engagement target.

Example: 1/4-20 UNC at a 75% theoretical target gives about 0.2013 in; the standard #7 chart drill is 0.2010 in.

Thread size Target thread engagement

Supported theoretical range: 50%–85%.

Calculated target hole 0.2013 in · 5.11 mm #7 is 0.0003 in smaller than the 75% theoretical target.

Standard chart drill: #7 · 0.2010 in · 5.11 mm
Chart-drill theoretical thread: 75.4%
Thread basis: 1/4-20 UNC · 20 TPI

How to Use a Tap Drill Chart

Match the full thread

Use both diameter and pitch/TPI. For example, 1/4-20 and 1/4-28 require different drills.

Use the listed tap drill

The named number, letter, fractional, or metric drill is the practical cutting-tap starting size.

Check special applications

For production, difficult material, deep holes, or critical tolerances, verify the exact tap manufacturer’s recommendation.

Show percent-thread formulas

Unified inch cutting tapsD_hole = D_major − (0.01299 × E ÷ TPI)

E is the desired percentage entered as a whole number, such as 75.

ISO metric cutting tapsD_hole = D_major − (E × P ÷ 76.98)

P is pitch in millimeters.

When the Standard Tap Drill Is Not the Final Answer

Cutting vs. forming taps

This chart is for cutting taps. Forming or roll taps displace material and normally require a larger, manufacturer-specific pre-hole.

Tap drill vs. clearance hole

A tap drill leaves material for internal threads. A clearance hole is larger so the fastener can pass through; the two charts are not interchangeable.

Production variables

Material, tap geometry, thread class, drill tolerance, runout, rigidity, coolant, and hole depth can change the preferred production pre-hole.

Sources and Reference Scope

The page keeps the standard chart values separate from the optional theoretical percent-thread calculation. The calculation follows the published cutting-tap formulas used by major tooling references; Unified and ISO references define the underlying thread systems.

MSC Industrial Supply — Types of Taps: A Practical GuidePublished cut-tap drill formulas, percent-thread calculation, and tap/drill reference.
OSG USA — Tap Drill Size & Pitch LimitsManufacturer chart library for tap-drill sizing and pitch limits.
ASME B1.1 — Unified Inch Screw ThreadsUnified inch thread-form and designation scope.
ISO 68-1 — ISO General Purpose Screw Threads — Basic ProfileISO metric 60° basic thread profile.
ISO 261 and ISO 262ISO metric diameter and pitch series.

Source check: October 4, 2026
Primary use: Common 60° cutting-tap starting sizes
Calculator: Theoretical percent-thread comparison
Excluded: Form taps, STI/helical-insert taps, special thread forms, process-specific production allowances

Tap Drill Chart Questions

What size drill do I use for a 1/4-20 tap?

Use a #7 drill, 0.2010 in (5.11 mm), as the conventional cutting-tap starting size for 1/4-20 UNC.

What size drill do I use for a 3/8-16 tap?

Use a 5/16 in drill, 0.3125 in (7.94 mm), as the conventional starting size for 3/8-16 UNC.

What is the tap drill for M6 × 1?

Use a 5.0 mm drill as the conventional starting size for an M6 × 1 cutting tap.

Why can the percent-thread calculator differ from the chart?

The chart preserves conventional drill recommendations. The calculator computes an idealized hole for the selected theoretical percentage of thread, so its target can fall between stocked drill sizes.

Can I use these sizes for a roll tap or forming tap?

No. Forming taps normally need a different, larger pre-hole. Use the forming-tap manufacturer’s recommendation for the exact tap and material.

Is a tap drill the same as a clearance drill?

No. A tap drill is smaller because it leaves material for internal threads. A clearance hole is sized so the screw or bolt can pass through.