Woodworking & Carpentry · Chart + finder

Drill Bit Size Chart

This drill bit size chart and finder gives you the right bit for wood screw pilot holes, lag screws, clearance holes and tap drills in one lookup. Pick a screw or thread and get the bit as a fraction, decimal and millimeter size.

Find a drill bit

Wood you are screwing into

Oak, maple, cherry, walnut, hickory

Countersink0.3320 inClearance hole11/64"Pilot hole1/8"Top boardBase board
Holes for a #8 flat head wood screw joining two boards. Hole sizes exaggerated for clarity.
Pilot bit, #8 screw in hardwood
1/8"
Decimal
0.1250in
Metric
3.17mm
Clearance hole
11/64"
0.1719 in, top board only
Countersink to
0.3320in
Head diameter, about 21/64"
Screw major dia.
0.1640in
Thread root dia.
0.1360in
The math
Pilot = 90% x root 0.136 in = 0.122 in, nearest bit 1/8" (0.1250)
Drill the pilot the full screw depth in hardwood. A pilot that stops short is the main cause of snapped screws and split ends.

How to choose a pilot hole size

A pilot hole removes just enough wood for the screw's core so the threads can cut into solid fiber. Too small and the screw splits the board, strips its head or snaps. Too big and the threads have nothing to bite.

Size the pilot to the root diameter, not the outside of the threads. The USDA Wood Handbook recommends a lead hole of about 90 percent of the root diameter in hardwoods and about 70 percent in softwoods. That is why hardwood needs a larger pilot: oak and maple fibers do not crush out of the way, so the screw has to cut its own path.

Not sure which bit type to buy for the job? Our guide on how to choose a drill bit covers brad points, twist bits and countersinks.

Rules of thumb
Hardwood pilot = 0.90 x root dia.
Softwood pilot = 0.70 x root dia.
Clearance > major dia.
Countersink = head dia.
Example: a #8 screw has a 0.136 in root. In oak, 0.90 x 0.136 = 0.122 in, so use a 1/8 in bit (0.125). In pine, 0.70 x 0.136 = 0.095 in, so use 3/32 in.

Pilot hole size chart for wood screws

Screw dimensions come from ASME B18.6.1. Pilot sizes are the Wood Handbook percentages rounded to the nearest 1/64 inch bit. Drill the clearance hole through the top board only, and countersink to the head diameter so a flat head sits flush.

Wood screw pilot hole, clearance hole and countersink sizes
ScrewMajor dia. (in)Hardwood pilotSoftwood pilotClearance holeCountersink (in)
#20.0861/16"3/64"3/32"0.172
#30.0995/64"1/16"7/64"0.199
#40.1125/64"1/16"1/8"0.225
#50.1253/32"5/64"9/64"0.252
#60.1387/64"5/64"9/64"0.279
#70.1517/64"3/32"5/32"0.305
#80.1641/8"3/32"11/64"0.332
#90.1771/8"7/64"3/16"0.358
#100.1909/64"7/64"13/64"0.385
#120.2165/32"1/8"7/32"0.438
#140.2423/16"9/64"1/4"0.507
Lag screw pilot and shank hole sizes
Lag screwShank holeSoftwood pilotHardwood pilot
1/4"1/4"5/32"11/64"
5/16"5/16"3/16"7/32"
3/8"3/8"1/4"9/32"
7/16"7/16"9/32"11/32"
1/2"1/2"5/16"13/32"

Clearance vs pilot vs countersink holes

Most wood screw joints need two or three different holes, and mixing them up is the most common reason a joint will not close.

  • Pilot hole: drilled into the board that holds the threads. It is smaller than the screw.
  • Clearance hole: drilled through the top board, slightly larger than the screw's major diameter. The screw slides through, so the head pulls the top board tight instead of the threads jacking the boards apart.
  • Countersink: a cone (82 degrees for inch screws) cut to the head diameter so a flat head sits flush. A combination countersink bit drills all three in one pass.

Driving lots of screws? Drill with a drill and drive with an impact driver. Our impact driver vs drill comparison explains why the two-tool setup is faster.

Tap drill chart: SAE and metric

Tap drills leave about 75 percent of full thread depth, which is the standard for mild steel, aluminum and brass. More thread adds almost no strength and makes taps break. Close fit clearance holes locate parts accurately; free fit holes give you room to line up several bolts.

Inch UNC and UNF tap drill chart
ThreadTap drillDecimalThread %CloseFree
#4-40 UNC#430.089071%#32#30
#4-48 UNF#420.093568%#32#30
#6-32 UNC#360.106578%#27#25
#6-40 UNF#330.113077%#27#25
#8-32 UNC#290.136069%#18#16
#8-36 UNF#290.136078%#18#16
#10-24 UNC#250.149575%#9#7
#10-32 UNF#210.159076%#9#7
#12-24 UNC#160.177072%#2#1
#12-28 UNF#140.182073%#2#1
1/4-20 UNC#70.201075%FH
1/4-28 UNF#30.213080%FH
5/16-18 UNCF0.257077%PQ
5/16-24 UNFI0.272075%PQ
3/8-16 UNC5/16"0.312577%WX
3/8-24 UNFQ0.332079%WX
7/16-14 UNCU0.368075%29/64"15/32"
7/16-20 UNF25/64"0.390672%29/64"15/32"
1/2-13 UNC27/64"0.421978%33/64"17/32"
1/2-20 UNF29/64"0.453172%33/64"17/32"
9/16-12 UNC31/64"0.484472%37/64"19/32"
9/16-18 UNF33/64"0.515665%37/64"19/32"
5/8-11 UNC17/32"0.531379%41/64"21/32"
5/8-18 UNF37/64"0.578165%41/64"21/32"
3/4-10 UNC21/32"0.656372%49/64"25/32"
3/4-16 UNF11/16"0.687577%49/64"25/32"
Metric coarse tap drill chart
ThreadTap drillNearest inchCloseFree
M3 x 0.52.5 mm#403.2 mm3.4 mm
M4 x 0.73.3 mm#304.3 mm4.5 mm
M5 x 0.84.2 mm#195.3 mm5.5 mm
M6 x 15 mm#96.4 mm6.6 mm
M8 x 1.256.8 mmH8.4 mm9 mm
M10 x 1.58.5 mmQ10.5 mm11 mm
M12 x 1.7510.2 mmY13 mm13.5 mm
M14 x 212 mm15/32"15 mm15.5 mm
M16 x 214 mm35/64"17 mm17.5 mm
M18 x 2.515.5 mm39/64"19 mm20 mm
M20 x 2.517.5 mm11/16"21 mm22 mm

Tapping in wood or plastic?

Threaded inserts, not tapped holes, are the right call in wood. Follow the insert maker's hole size, which is usually close to the insert's root diameter.

Drill bit size chart: fraction, number and letter sizes

This conversion chart lists every fractional bit from 1/64 to 1/2 inch, number drills #1 to #60 and letter drills A to Z, sorted small to large with decimal inch and millimeter sizes. Number and letter decimals are the ASME B94.11M values printed in Machinery's Handbook.

How to read it: find the decimal size you need, then use whichever bit lands on or just above it. Numbers get smaller as the bit gets bigger, and #1 (0.228 in) hands off to letter A (0.234 in).

Drill bit size chart, part 1
SizeTypeDecimal (in)mm
1/64"Fraction0.01560.40
1/32"Fraction0.03130.79
#60Number0.04001.02
#59Number0.04101.04
#58Number0.04201.07
#57Number0.04301.09
#56Number0.04651.18
3/64"Fraction0.04691.19
#55Number0.05201.32
#54Number0.05501.40
#53Number0.05951.51
1/16"Fraction0.06251.59
#52Number0.06351.61
#51Number0.06701.70
#50Number0.07001.78
#49Number0.07301.85
#48Number0.07601.93
5/64"Fraction0.07811.98
#47Number0.07851.99
#46Number0.08102.06
#45Number0.08202.08
#44Number0.08602.18
#43Number0.08902.26
#42Number0.09352.37
3/32"Fraction0.09382.38
#41Number0.09602.44
#40Number0.09802.49
#39Number0.09952.53
#38Number0.10152.58
#37Number0.10402.64
#36Number0.10652.71
7/64"Fraction0.10942.78
#35Number0.11002.79
#34Number0.11102.82
#33Number0.11302.87
#32Number0.11602.95
#31Number0.12003.05
1/8"Fraction0.12503.17
#30Number0.12853.26
#29Number0.13603.45
#28Number0.14053.57
9/64"Fraction0.14063.57
#27Number0.14403.66
#26Number0.14703.73
#25Number0.14953.80
#24Number0.15203.86
#23Number0.15403.91
5/32"Fraction0.15633.97
#22Number0.15703.99
#21Number0.15904.04
#20Number0.16104.09
#19Number0.16604.22
#18Number0.16954.31
11/64"Fraction0.17194.37
#17Number0.17304.39
#16Number0.17704.50
#15Number0.18004.57
#14Number0.18204.62
#13Number0.18504.70
Drill bit size chart, part 2
SizeTypeDecimal (in)mm
3/16"Fraction0.18754.76
#12Number0.18904.80
#11Number0.19104.85
#10Number0.19354.91
#9Number0.19604.98
#8Number0.19905.05
#7Number0.20105.11
13/64"Fraction0.20315.16
#6Number0.20405.18
#5Number0.20555.22
#4Number0.20905.31
#3Number0.21305.41
7/32"Fraction0.21885.56
#2Number0.22105.61
#1Number0.22805.79
ALetter0.23405.94
15/64"Fraction0.23445.95
BLetter0.23806.05
CLetter0.24206.15
DLetter0.24606.25
1/4"Fraction0.25006.35
ELetter0.25006.35
FLetter0.25706.53
GLetter0.26106.63
17/64"Fraction0.26566.75
HLetter0.26606.76
ILetter0.27206.91
JLetter0.27707.04
KLetter0.28107.14
9/32"Fraction0.28137.14
LLetter0.29007.37
MLetter0.29507.49
19/64"Fraction0.29697.54
NLetter0.30207.67
5/16"Fraction0.31257.94
OLetter0.31608.03
PLetter0.32308.20
21/64"Fraction0.32818.33
QLetter0.33208.43
RLetter0.33908.61
11/32"Fraction0.34388.73
SLetter0.34808.84
TLetter0.35809.09
23/64"Fraction0.35949.13
ULetter0.36809.35
3/8"Fraction0.37509.52
VLetter0.37709.58
WLetter0.38609.80
25/64"Fraction0.39069.92
XLetter0.397010.1
YLetter0.404010.3
13/32"Fraction0.406310.3
ZLetter0.413010.5
27/64"Fraction0.421910.7
7/16"Fraction0.437511.1
29/64"Fraction0.453111.5
15/32"Fraction0.468811.9
31/64"Fraction0.484412.3
1/2"Fraction0.500012.7

Tips for cleaner, more accurate holes

  • Flag your depth. Wrap painter's tape around the bit at the screw length and stop when the flag touches the surface. A stop collar is better for repeat work.
  • Drill slow in metal. About 1,200 RPM for a 1/4 inch bit in mild steel, and slower as bits get bigger. Smoke and blue chips mean you are going too fast.
  • Use cutting oil in steel and when tapping. It keeps the edge cool and the chips moving. Aluminum likes WD-40 or kerosene.
  • Wax the screw in oak and other dense woods. It cuts driving torque noticeably.
  • Keep the bit square. For tapped holes and dowels, a drill press beats a handheld drill every time. For site work, a good cordless drill with a clutch and a low speed range is all you need.

Bookmark this drill bit size chart for your next project, and if you are buying lumber for it, run your stock through the board foot calculator before you head to the yard.

Frequently asked questions

What size drill bit do I use for a #8 wood screw?

Use a 1/8 inch pilot bit in hardwood and a 3/32 inch pilot bit in softwood. If the top board needs a clearance hole so the screw can pull the joint tight, drill it with an 11/64 inch bit.

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

Use a #7 drill (0.201 in), which leaves about 75 percent thread. If you only own fractional bits, a 13/64 inch bit (0.203 in) is the closest substitute and still leaves about 72 percent thread.

What size pilot hole for a 3/8 inch lag screw?

Drill a 1/4 inch pilot in softwood framing lumber and a 9/32 inch pilot in dense hardwood. Drill a 3/8 inch shank hole through the part you are attaching and as deep as the smooth shank.

Why does hardwood need a bigger pilot hole than softwood?

Dense hardwood fibers do not compress out of the way the way pine does. A pilot close to the thread root diameter (about 90 percent) lets the threads cut in without splitting the board or snapping the screw, while softwood holds better with a smaller pilot (about 70 percent of the root).

What is the difference between number, letter and fractional drill bits?

They are three sizing systems that fill in each other’s gaps. Number drills run from #80 (tiny) to #1 (0.228 in), letter drills run from A (0.234 in) to Z (0.413 in), and fractional bits step in 1/64 inch increments. Machinists use number and letter drills for tap and clearance holes where a fractional size would be too loose or too tight.

What size drill bit for an M6 tap?

Use a 5 mm drill for an M6 x 1.0 coarse thread. The closest inch bit is a #9 (0.196 in). For a bolt clearance hole, use 6.4 mm for a close fit or 6.6 mm for a normal fit.

Gear for this job

Our research-backed picks
Tool reviewBest Cordless DrillsA clutch and a true low speed range matter more than peak torque for pilot holes.Read the guideTool reviewBest Drill PressesSquare, repeatable holes for tapping, doweling and hardware.Read the guideComparisonImpact Driver vs DrillWhich tool drills the hole and which one drives the screw.Read the guide

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