What is a 3/8" drill in decimal and mm?

0.3750 in, or 9.525 mm; nearest number / letter drill: Letter V (0.3770 in, +0.0020 in); nearest metric drill: 9.5 mm (0.3740 in, -0.0010 in).

What RPM for a 3/8" drill in steel?

In low-carbon steel (1018) an HSS 3/8" drill (0.3750 in) runs about 920 RPM at 90 SFM; a carbide drill about 3,060 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 3/8" drill?

About 0.0095 in/rev in mild steel, 0.0085 in/rev in aluminum and 0.0063 in/rev in 304 stainless. At 920 RPM that is 8.74 IPM in steel (IPM = RPM × IPR).

What RPM for a 3/8" drill in aluminum?

2,550 RPM with HSS (250 SFM) or up to 6,110 RPM with carbide (600 SFM), feeding about 0.0085 in/rev.

What size is a 3/8" drill?

0.3750 in / 9.525 mm. The nearest other drills are 9.5 mm (0.3740 in), Letter V (0.3770 in), 9.6 mm (0.3780 in).

3/8" drill size

A 3/8" fractional drill is 0.3750 in (9.525 mm).

Decimal inch: 0.3750
Millimeters: 9.525
Nearest 1/64: 3/8" (+0.0000)
Type: fractional drill

Nearest equivalents in other systems

Drills closest to 3/8"
System	Drill	Inch	mm	Difference
Number / letter	Letter V	0.3770	9.576	+0.0020 in
Metric	9.5 mm	0.3740	9.500	-0.0010 in

Speeds and feeds: in mild steel an HSS drill starts at about 920 RPM and 0.0095 in/rev (8.74 IPM); in 6061 aluminum about 2,550 RPM.

3/8" drill speeds and feeds by material

Jobber-length twist drill, D = 0.3750 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

3/8" drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	2,550	600	6,110	0.0085	21.7	51.9
Brass / free-machining	150	1,530	400	4,070	0.0063	9.64	25.6
Low-carbon steel (1018)	90	920	300	3,060	0.0095	8.74	29.1
Alloy steel (4140, annealed)	70	710	250	2,550	0.0105	7.46	26.8
Stainless 304	40	410	150	1,530	0.0063	2.58	9.64
Gray cast iron	80	810	250	2,550	0.0065	5.27	16.6
Titanium 6Al-4V	25	250	100	1,020	0.0043	1.08	4.39
Plastics (acetal)	300	3,060	500	5,090	0.0050	15.3	25.4

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 920 RPM × 0.241 mm/rev = 222 mm/min.

Worked example: 3/8" drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.3750 ≈ 920 RPM.
Feed for a 0.375 in drill in mild steel ≈ 0.0095 in/rev.
IPM = 920 × 0.0095 = 8.74 IPM.

Peck cycle by hole depth

3/8" drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 1.125 in (28.6 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 1.875 in (47.6 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 3.000 in (76.2 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 3/8" drill

No standard UNC, UNF or metric tap in our tables calls for a 3/8" drill. Use it for clearance, pilot or reamer prep holes.

Nearest drills

9.5 mm: 0.3740 in / 9.500 mm (-0.0010 in)
Letter V: 0.3770 in / 9.576 mm (+0.0020 in)
9.6 mm: 0.3780 in / 9.600 mm (+0.0029 in)
9.4 mm: 0.3701 in / 9.400 mm (-0.0049 in)

Drill speed calculator, prefilled for 3/8"Drill finder: sizes near 3/8"Fractional drill chart Decimal equivalent chart

Common questions

What is a 3/8" drill in decimal and mm?: 0.3750 in, or 9.525 mm; nearest number / letter drill: Letter V (0.3770 in, +0.0020 in); nearest metric drill: 9.5 mm (0.3740 in, -0.0010 in).
What RPM for a 3/8" drill in steel?: In low-carbon steel (1018) an HSS 3/8" drill (0.3750 in) runs about 920 RPM at 90 SFM; a carbide drill about 3,060 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 3/8" drill?: About 0.0095 in/rev in mild steel, 0.0085 in/rev in aluminum and 0.0063 in/rev in 304 stainless. At 920 RPM that is 8.74 IPM in steel (IPM = RPM × IPR).
What RPM for a 3/8" drill in aluminum?: 2,550 RPM with HSS (250 SFM) or up to 6,110 RPM with carbide (600 SFM), feeding about 0.0085 in/rev.
What size is a 3/8" drill?: 0.3750 in / 9.525 mm. The nearest other drills are 9.5 mm (0.3740 in), Letter V (0.3770 in), 9.6 mm (0.3780 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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