What is a 1" drill in decimal and mm?

1.0000 in, or 25.400 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.5870 in); nearest metric drill: 25.5 mm (1.0039 in, +0.0039 in).

What RPM for a 1" drill in steel?

In low-carbon steel (1018) an HSS 1" drill (1.0000 in) runs about 340 RPM at 90 SFM; a carbide drill about 1,150 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 1" drill?

About 0.0125 in/rev in mild steel, 0.0130 in/rev in aluminum and 0.0105 in/rev in 304 stainless. At 340 RPM that is 4.25 IPM in steel (IPM = RPM × IPR).

What RPM for a 1" drill in aluminum?

950 RPM with HSS (250 SFM) or up to 2,290 RPM with carbide (600 SFM), feeding about 0.0130 in/rev.

1" drill size

A 1" fractional drill is 1.0000 in (25.400 mm). It is the cut tap, 75% thread drill for 1-1/8-8.

Decimal inch: 1.0000
Millimeters: 25.400
Nearest 1/64: 1" (+0.0000)
Type: fractional drill

Nearest equivalents in other systems

Drills closest to 1"
System	Drill	Inch	mm	Difference
Number / letter	Letter Z	0.4130	10.490	-0.5870 in
Metric	25.5 mm	1.0039	25.500	+0.0039 in

Speeds and feeds: in mild steel an HSS drill starts at about 340 RPM and 0.0125 in/rev (4.25 IPM); in 6061 aluminum about 950 RPM.

1" drill speeds and feeds by material

Jobber-length twist drill, D = 1.0000 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

1" drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	950	600	2,290	0.0130	12.3	29.8
Brass / free-machining	150	570	400	1,530	0.0100	5.70	15.3
Low-carbon steel (1018)	90	340	300	1,150	0.0125	4.25	14.4
Alloy steel (4140, annealed)	70	270	250	950	0.0130	3.51	12.3
Stainless 304	40	150	150	570	0.0105	1.58	5.99
Gray cast iron	80	310	250	950	0.0110	3.41	10.4
Titanium 6Al-4V	25	100	100	380	0.0060	0.60	2.28
Plastics (acetal)	300	1,150	500	1,910	0.0080	9.20	15.3

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 340 RPM × 0.318 mm/rev = 108 mm/min.

Worked example: 1" drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 1.0000 ≈ 340 RPM.
Feed for a 1.000 in drill in mild steel ≈ 0.0125 in/rev.
IPM = 340 × 0.0125 = 4.25 IPM.

Peck cycle by hole depth

1" drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 3.000 in (76.2 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 5.000 in (127 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 8.000 in (203.2 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 1" drill

1-1/8-8 — cut tap, 75% thread

Nearest drills

25.5 mm: 1.0039 in / 25.500 mm (+0.0039 in)
25.25 mm: 0.9941 in / 25.250 mm (-0.0059 in)
25.75 mm: 1.0138 in / 25.750 mm (+0.0138 in)
63/64": 0.9844 in / 25.003 mm (-0.0156 in)

Drill speed calculator, prefilled for 1"Drill finder: sizes near 1"Fractional drill chart Decimal equivalent chart

Common questions

What is a 1" drill in decimal and mm?: 1.0000 in, or 25.400 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.5870 in); nearest metric drill: 25.5 mm (1.0039 in, +0.0039 in).
What RPM for a 1" drill in steel?: In low-carbon steel (1018) an HSS 1" drill (1.0000 in) runs about 340 RPM at 90 SFM; a carbide drill about 1,150 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 1" drill?: About 0.0125 in/rev in mild steel, 0.0130 in/rev in aluminum and 0.0105 in/rev in 304 stainless. At 340 RPM that is 4.25 IPM in steel (IPM = RPM × IPR).
What RPM for a 1" drill in aluminum?: 950 RPM with HSS (250 SFM) or up to 2,290 RPM with carbide (600 SFM), feeding about 0.0130 in/rev.
What tap uses a 1" drill?: 1-1/8-8 (cut tap, 75% thread).

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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