What is a #23 drill in decimal and mm?

0.1540 in, or 3.912 mm; nearest fractional drill: 5/32" (0.1563 in, +0.0022 in); nearest metric drill: 3.9 mm (0.1535 in, -0.0005 in).

What RPM for a #23 drill in steel?

In low-carbon steel (1018) an HSS #23 drill (0.1540 in) runs about 2,230 RPM at 90 SFM; a carbide drill about 7,440 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a #23 drill?

About 0.0038 in/rev in mild steel, 0.0036 in/rev in aluminum and 0.0025 in/rev in 304 stainless. At 2,230 RPM that is 8.47 IPM in steel (IPM = RPM × IPR).

What RPM for a #23 drill in aluminum?

6,200 RPM with HSS (250 SFM) or up to 14,880 RPM with carbide (600 SFM), feeding about 0.0036 in/rev.

What size is a #23 drill?

0.1540 in / 3.912 mm. The nearest other drills are 3.9 mm (0.1535 in), #24 (0.1520 in), 5/32" (0.1563 in).

#23 drill size

A #23 number (wire-gauge) drill is 0.1540 in (3.912 mm).

Decimal inch: 0.1540
Millimeters: 3.912
Nearest 1/64: 5/32" (-0.0023)
Type: number (wire-gauge) drill

Nearest equivalents in other systems

Drills closest to #23
System	Drill	Inch	mm	Difference
Fractional	5/32"	0.1563	3.969	+0.0022 in
Metric	3.9 mm	0.1535	3.900	-0.0005 in

Speeds and feeds: in mild steel an HSS drill starts at about 2,230 RPM and 0.0038 in/rev (8.47 IPM); in 6061 aluminum about 6,200 RPM.

#23 drill speeds and feeds by material

Jobber-length twist drill, D = 0.1540 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

#23 drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	6,200	600	14,880	0.0036	22.3	53.6
Brass / free-machining	150	3,720	400	9,920	0.0031	11.5	30.8
Low-carbon steel (1018)	90	2,230	300	7,440	0.0038	8.47	28.3
Alloy steel (4140, annealed)	70	1,740	250	6,200	0.0038	6.61	23.6
Stainless 304	40	990	150	3,720	0.0025	2.48	9.30
Gray cast iron	80	1,980	250	6,200	0.0024	4.75	14.9
Titanium 6Al-4V	25	620	100	2,480	0.0019	1.18	4.71
Plastics (acetal)	300	7,440	500	12,400	0.0048	35.7	59.5

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 2,230 RPM × 0.097 mm/rev = 215 mm/min.

Worked example: #23 drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.1540 ≈ 2,230 RPM.
Feed for a 0.154 in drill in mild steel ≈ 0.0038 in/rev.
IPM = 2,230 × 0.0038 = 8.47 IPM.

Peck cycle by hole depth

#23 drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 0.462 in (11.7 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 0.770 in (19.6 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 1.232 in (31.3 mm)	G83 full retract	0.5-1 × D, shrinking with depth	Retract to clear chips; reduce feed ~10-20% past 5×D.

Taps that use a #23 drill

No standard UNC, UNF or metric tap in our tables calls for a #23 drill. Use it for clearance, pilot or reamer prep holes.

Nearest drills

3.9 mm: 0.1535 in / 3.900 mm (-0.0005 in)
#24: 0.1520 in / 3.861 mm (-0.0020 in)
5/32": 0.1563 in / 3.969 mm (+0.0022 in)
#22: 0.1570 in / 3.988 mm (+0.0030 in)

Drill speed calculator, prefilled for #23 Drill finder: sizes near #23 Number drill chart Decimal equivalent chart

Common questions

What is a #23 drill in decimal and mm?: 0.1540 in, or 3.912 mm; nearest fractional drill: 5/32" (0.1563 in, +0.0022 in); nearest metric drill: 3.9 mm (0.1535 in, -0.0005 in).
What RPM for a #23 drill in steel?: In low-carbon steel (1018) an HSS #23 drill (0.1540 in) runs about 2,230 RPM at 90 SFM; a carbide drill about 7,440 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a #23 drill?: About 0.0038 in/rev in mild steel, 0.0036 in/rev in aluminum and 0.0025 in/rev in 304 stainless. At 2,230 RPM that is 8.47 IPM in steel (IPM = RPM × IPR).
What RPM for a #23 drill in aluminum?: 6,200 RPM with HSS (250 SFM) or up to 14,880 RPM with carbide (600 SFM), feeding about 0.0036 in/rev.
What size is a #23 drill?: 0.1540 in / 3.912 mm. The nearest other drills are 3.9 mm (0.1535 in), #24 (0.1520 in), 5/32" (0.1563 in).

Nearby drill sizes

Sources

Machinery's Handbook, 31st ed., Speeds and Feeds for Drilling, Reaming and Threading (Tables 17-23) — HSS and carbide drilling SFM (rounded).
RedLine Tools (Productivity Inc.) catalog p. 340, Cobalt & HSS Drills Speeds & Feeds — feed per rev by drill diameter and material (middle of the catalog range).
ASME B94.11M twist drills: number (#1-#80) and letter (A-Z) drill sizes; drill size reference.

Material feed multipliers (aluminum 1.3×, brass 1.1×, 4140 0.85×, stainless and titanium 0.7× the mild-steel feed) are JobLine estimates. Peck guidance is JobLine shop practice. Use your drill maker's data first.

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