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Drill bit size chart

Type any size as a fraction, decimal, millimeters, or a number or letter drill. You get it in every system, the nearest drill in each series and the drills on either side, drawn to scale. The full charts follow.

By WorkbenchPilot · Updated October 12, 2026 · Decimal equivalents from Starrett
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Fractions like 5/16 or 1-1/4, decimals like 0.25, millimeters like 6.5, or a number or letter drill like 7 or F.

HOLES, ACTUAL PROPORTIONSDRAWN TO SCALE
Size.3125 in
As a fraction
Nearest fraction drill
Nearest number drill
Nearest letter drill
Nearest metric (0.1 mm)
Tap drill for
The answer

Drill bits come in four series. Fraction drills go up in 1/64 in steps. Number drills run from #80 (0.0135 in) up to #1 (0.228 in), getting bigger as the number gets smaller. Letter drills pick up from A (0.234 in) to Z (0.413 in). Metric drills are sized in millimeters. Number and letter drills fill the gaps between fractions, which is why so many tap drills are numbers or letters.

.201 in#7 (1/4-20 tap)
.250 inE = 1/4 in
.257 inF (5/16-18 tap)
6.35 mm1/4 in

How the four series fit together

  • Fractions are the sizes in an ordinary drill set: 1/16, 5/64, 3/32 and so on up to 1/2 in, then larger. Each step is 1/64 in (0.0156 in, about 0.4 mm).
  • Number drills go the other way: #80 is the smallest and #1 the largest. Between #60 and #1 they are spaced only a few thousandths of an inch apart, close enough to hit the exact size a tap or a screw needs.
  • Letter drills continue above #1: A is 0.234 in and Z is 0.413 in. E is exactly 1/4 in.
  • Metric drills are sized in millimeters. An inch is exactly 25.4 mm, so a 1/4 in drill is 6.35 mm and the closest metric drill is 6.4 mm.

Number drill sizes

Number drillInchesMillimetersNearest fraction
#80.01350.341/64 in
#79.01450.371/64 in
#78.01600.411/64 in
#77.01800.461/64 in
#76.02000.511/64 in
#75.02100.531/64 in
#74.02250.571/64 in
#73.02400.611/32 in
#72.02500.641/32 in
#71.02600.661/32 in
#70.02800.711/32 in
#69.02920.741/32 in
#68.03100.791/32 in
#67.03200.811/32 in
#66.03300.841/32 in
#65.03500.891/32 in
#64.03600.911/32 in
#63.03700.941/32 in
#62.03800.971/32 in
#61.03900.991/32 in
#60.04001.023/64 in
#59.04101.043/64 in
#58.04201.073/64 in
#57.04301.093/64 in
#56.04651.183/64 in
#55.05201.323/64 in
#54.05501.401/16 in
#53.05951.511/16 in
#52.06351.611/16 in
#51.06701.701/16 in
#50.07001.781/16 in
#49.07301.855/64 in
#48.07601.935/64 in
#47.07851.995/64 in
#46.08102.065/64 in
#45.08202.085/64 in
#44.08602.183/32 in
#43.08902.263/32 in
#42.09352.373/32 in
#41.09602.443/32 in
#40.09802.493/32 in
#39.09952.533/32 in
#38.10152.583/32 in
#37.10402.647/64 in
#36.10652.717/64 in
#35.11002.797/64 in
#34.11102.827/64 in
#33.11302.877/64 in
#32.11602.957/64 in
#31.12003.051/8 in
#30.12853.261/8 in
#29.13603.459/64 in
#28.14053.579/64 in
#27.14403.669/64 in
#26.14703.739/64 in
#25.14953.805/32 in
#24.15203.865/32 in
#23.15403.915/32 in
#22.15703.995/32 in
#21.15904.045/32 in
#20.16104.095/32 in
#19.16604.2211/64 in
#18.16954.3111/64 in
#17.17304.3911/64 in
#16.17704.5011/64 in
#15.18004.573/16 in
#14.18204.623/16 in
#13.18504.703/16 in
#12.18904.803/16 in
#11.19104.853/16 in
#10.19354.913/16 in
#9.19604.9813/64 in
#8.19905.0513/64 in
#7.20105.1113/64 in
#6.20405.1813/64 in
#5.20555.2213/64 in
#4.20905.3113/64 in
#3.21305.417/32 in
#2.22105.617/32 in
#1.22805.7915/64 in

Decimal equivalents from Starrett’s chart; millimeters converted at 25.4 mm to the inch. Shaded rows are common tap drills (#7 for 1/4-20, #21 for 10-32, #25 for 10-24, #29 for 8-32, #36 for 6-32, #43 for 4-40).

Letter drill sizes

Letter drillInchesMillimetersNearest fraction
A.23405.9415/64 in
B.23806.0515/64 in
C.24206.1515/64 in
D.24606.251/4 in
E.25006.351/4 in
F.25706.531/4 in
G.26106.6317/64 in
H.26606.7617/64 in
I.27206.9117/64 in
J.27707.049/32 in
K.28107.149/32 in
L.29007.3719/64 in
M.29507.4919/64 in
N.30207.6719/64 in
O.31608.035/16 in
P.32308.2021/64 in
Q.33208.4321/64 in
R.33908.6111/32 in
S.34808.8411/32 in
T.35809.0923/64 in
U.36809.353/8 in
V.37709.583/8 in
W.38609.8025/64 in
X.397010.0825/64 in
Y.404010.2613/32 in
Z.413010.4913/32 in

From Starrett. Shaded: F (5/16-18 tap and the close-fit hole for a 1/4 in bolt), I (5/16-24), Q (3/8-24), U (7/16-14).

Fraction drill sizes, 1/64 to 1 in

FractionInchesMillimeters
1/64 in.01560.40
1/32 in.03120.79
3/64 in.04691.19
1/16 in.06251.59
5/64 in.07811.98
3/32 in.09382.38
7/64 in.10942.78
1/8 in.12503.17
9/64 in.14063.57
5/32 in.15623.97
11/64 in.17194.37
3/16 in.18754.76
13/64 in.20315.16
7/32 in.21885.56
15/64 in.23445.95
1/4 in.25006.35
17/64 in.26566.75
9/32 in.28127.14
19/64 in.29697.54
5/16 in.31257.94
21/64 in.32818.33
11/32 in.34388.73
23/64 in.35949.13
3/8 in.37509.52
25/64 in.39069.92
13/32 in.406210.32
27/64 in.421910.72
7/16 in.437511.11
29/64 in.453111.51
15/32 in.468811.91
31/64 in.484412.30
1/2 in.500012.70
33/64 in.515613.10
17/32 in.531213.49
35/64 in.546913.89
9/16 in.562514.29
37/64 in.578114.68
19/32 in.593815.08
39/64 in.609415.48
5/8 in.625015.88
41/64 in.640616.27
21/32 in.656216.67
43/64 in.671917.07
11/16 in.687517.46
45/64 in.703117.86
23/32 in.718818.26
47/64 in.734418.65
3/4 in.750019.05
49/64 in.765619.45
25/32 in.781219.84
51/64 in.796920.24
13/16 in.812520.64
53/64 in.828121.03
27/32 in.843821.43
55/64 in.859421.83
7/8 in.875022.22
57/64 in.890622.62
29/32 in.906223.02
59/64 in.921923.42
15/16 in.937523.81
61/64 in.953124.21
31/32 in.968824.61
63/64 in.984425.00
1 in1.000025.40

Metric drills

Metric drills come in 0.1 mm steps in most of the range used for screws and taps, and the converter above gives the nearest one. Some useful matches: a 5 mm drill is 0.1969 in, between a #9 (0.196 in) and a #8 (0.199 in); a 6 mm drill is 0.2362 in, between an A (0.234 in) and a B (0.238 in); a 10 mm drill is 0.3937 in, just under an X (0.397 in).

For metric taps, the tap drill size chart lists the drill for each thread, M1.6 to M12.

Questions people ask

What size is a #7 drill bit?

0.201 in, or 5.11 mm. It is the standard tap drill for a 1/4-20 thread.

Is a 1/4 in drill bit the same as a letter E?

Yes. Letter E is 0.250 in, exactly 1/4 in.

What size is a letter F drill?

0.257 in, or 6.53 mm: the tap drill for 5/16-18 and the close-fit clearance hole for a 1/4 in bolt.

What is 7/32 in a decimal?

0.2188 in (0.21875 exactly), or 5.56 mm.

What drill bit is closest to 5 mm?

A #9 (0.196 in, 4.98 mm). 5 mm is 0.1969 in.

What size is a #29 drill?

0.136 in, or 3.45 mm: the tap drill for 8-32 and 8-36 threads.

Sources

Checked October 12, 2026.