What is a #28 drill in decimal and mm?

0.1405 in, or 3.569 mm; nearest fractional drill: 9/64" (0.1406 in, +0.0001 in); nearest metric drill: 3.6 mm (0.1417 in, +0.0012 in).

What RPM for a #28 drill in steel?

In low-carbon steel (1018) an HSS #28 drill (0.1405 in) runs about 2,450 RPM at 90 SFM; a carbide drill about 8,160 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a #28 drill?

About 0.0034 in/rev in mild steel, 0.0032 in/rev in aluminum and 0.0023 in/rev in 304 stainless. At 2,450 RPM that is 8.33 IPM in steel (IPM = RPM × IPR).

What RPM for a #28 drill in aluminum?

6,800 RPM with HSS (250 SFM) or up to 16,310 RPM with carbide (600 SFM), feeding about 0.0032 in/rev.

What size is a #28 drill?

0.1405 in / 3.569 mm. The nearest other drills are 9/64" (0.1406 in), 3.6 mm (0.1417 in), 3.5 mm (0.1378 in).

#28 drill size

A #28 number (wire-gauge) drill is 0.1405 in (3.569 mm).

Decimal inch: 0.1405
Millimeters: 3.569
Nearest 1/64: 9/64" (-0.0001)
Type: number (wire-gauge) drill

Nearest equivalents in other systems

Drills closest to #28
System	Drill	Inch	mm	Difference
Fractional	9/64"	0.1406	3.572	+0.0001 in
Metric	3.6 mm	0.1417	3.600	+0.0012 in

Speeds and feeds: in mild steel an HSS drill starts at about 2,450 RPM and 0.0034 in/rev (8.33 IPM); in 6061 aluminum about 6,800 RPM.

#28 drill speeds and feeds by material

Jobber-length twist drill, D = 0.1405 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

#28 drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	6,800	600	16,310	0.0032	21.8	52.2
Brass / free-machining	150	4,080	400	10,870	0.0028	11.4	30.4
Low-carbon steel (1018)	90	2,450	300	8,160	0.0034	8.33	27.7
Alloy steel (4140, annealed)	70	1,900	250	6,800	0.0034	6.46	23.1
Stainless 304	40	1,090	150	4,080	0.0023	2.51	9.38
Gray cast iron	80	2,170	250	6,800	0.0021	4.56	14.3
Titanium 6Al-4V	25	680	100	2,720	0.0017	1.16	4.62
Plastics (acetal)	300	8,160	500	13,590	0.0049	40.0	66.6

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 2,450 RPM × 0.086 mm/rev = 212 mm/min.

Worked example: #28 drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.1405 ≈ 2,450 RPM.
Feed for a 0.141 in drill in mild steel ≈ 0.0034 in/rev.
IPM = 2,450 × 0.0034 = 8.33 IPM.

Peck cycle by hole depth

#28 drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 0.422 in (10.7 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 0.703 in (17.8 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 1.124 in (28.6 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 #28 drill

No standard UNC, UNF or metric tap in our tables calls for a #28 drill. Use it for clearance, pilot or reamer prep holes.

Nearest drills

9/64": 0.1406 in / 3.572 mm (+0.0001 in)
3.6 mm: 0.1417 in / 3.600 mm (+0.0012 in)
3.5 mm: 0.1378 in / 3.500 mm (-0.0027 in)
#27: 0.1440 in / 3.658 mm (+0.0035 in)

Drill speed calculator, prefilled for #28 Drill finder: sizes near #28 Number drill chart Decimal equivalent chart

Common questions

What is a #28 drill in decimal and mm?: 0.1405 in, or 3.569 mm; nearest fractional drill: 9/64" (0.1406 in, +0.0001 in); nearest metric drill: 3.6 mm (0.1417 in, +0.0012 in).
What RPM for a #28 drill in steel?: In low-carbon steel (1018) an HSS #28 drill (0.1405 in) runs about 2,450 RPM at 90 SFM; a carbide drill about 8,160 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a #28 drill?: About 0.0034 in/rev in mild steel, 0.0032 in/rev in aluminum and 0.0023 in/rev in 304 stainless. At 2,450 RPM that is 8.33 IPM in steel (IPM = RPM × IPR).
What RPM for a #28 drill in aluminum?: 6,800 RPM with HSS (250 SFM) or up to 16,310 RPM with carbide (600 SFM), feeding about 0.0032 in/rev.
What size is a #28 drill?: 0.1405 in / 3.569 mm. The nearest other drills are 9/64" (0.1406 in), 3.6 mm (0.1417 in), 3.5 mm (0.1378 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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