What is a 7/8" drill in decimal and mm?

0.8750 in, or 22.225 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.4620 in); nearest metric drill: 22.25 mm (0.8760 in, +0.0010 in).

What RPM for a 7/8" drill in steel?

In low-carbon steel (1018) an HSS 7/8" drill (0.8750 in) runs about 390 RPM at 90 SFM; a carbide drill about 1,310 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 7/8" drill?

About 0.0120 in/rev in mild steel, 0.0120 in/rev in aluminum and 0.0100 in/rev in 304 stainless. At 390 RPM that is 4.68 IPM in steel (IPM = RPM × IPR).

What RPM for a 7/8" drill in aluminum?

1,090 RPM with HSS (250 SFM) or up to 2,620 RPM with carbide (600 SFM), feeding about 0.0120 in/rev.

7/8" drill size

A 7/8" fractional drill is 0.8750 in (22.225 mm). It is the cut tap, 75% thread drill for 1"-8.

Decimal inch: 0.8750
Millimeters: 22.225
Nearest 1/64: 7/8" (+0.0000)
Type: fractional drill

Nearest equivalents in other systems

Drills closest to 7/8"
System	Drill	Inch	mm	Difference
Number / letter	Letter Z	0.4130	10.490	-0.4620 in
Metric	22.25 mm	0.8760	22.250	+0.0010 in

Speeds and feeds: in mild steel an HSS drill starts at about 390 RPM and 0.0120 in/rev (4.68 IPM); in 6061 aluminum about 1,090 RPM.

7/8" drill speeds and feeds by material

Jobber-length twist drill, D = 0.8750 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

7/8" drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	1,090	600	2,620	0.0120	13.1	31.4
Brass / free-machining	150	650	400	1,750	0.0095	6.18	16.6
Low-carbon steel (1018)	90	390	300	1,310	0.0120	4.68	15.7
Alloy steel (4140, annealed)	70	310	250	1,090	0.0125	3.88	13.6
Stainless 304	40	170	150	650	0.0100	1.70	6.50
Gray cast iron	80	350	250	1,090	0.0105	3.68	11.4
Titanium 6Al-4V	25	110	100	440	0.0058	0.64	2.55
Plastics (acetal)	300	1,310	500	2,180	0.0075	9.82	16.4

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 390 RPM × 0.305 mm/rev = 119 mm/min.

Worked example: 7/8" drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.8750 ≈ 390 RPM.
Feed for a 0.875 in drill in mild steel ≈ 0.0120 in/rev.
IPM = 390 × 0.0120 = 4.68 IPM.

Peck cycle by hole depth

7/8" drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 2.625 in (66.7 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 4.375 in (111.1 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 7.000 in (177.8 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 7/8" drill

1"-8 — cut tap, 75% thread · tap speeds and feeds

Nearest drills

22.25 mm: 0.8760 in / 22.250 mm (+0.0010 in)
22.0 mm: 0.8661 in / 22.000 mm (-0.0089 in)
22.5 mm: 0.8858 in / 22.500 mm (+0.0108 in)
55/64": 0.8594 in / 21.828 mm (-0.0156 in)

Drill speed calculator, prefilled for 7/8"Drill finder: sizes near 7/8"Fractional drill chart Decimal equivalent chart

Common questions

What is a 7/8" drill in decimal and mm?: 0.8750 in, or 22.225 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.4620 in); nearest metric drill: 22.25 mm (0.8760 in, +0.0010 in).
What RPM for a 7/8" drill in steel?: In low-carbon steel (1018) an HSS 7/8" drill (0.8750 in) runs about 390 RPM at 90 SFM; a carbide drill about 1,310 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 7/8" drill?: About 0.0120 in/rev in mild steel, 0.0120 in/rev in aluminum and 0.0100 in/rev in 304 stainless. At 390 RPM that is 4.68 IPM in steel (IPM = RPM × IPR).
What RPM for a 7/8" drill in aluminum?: 1,090 RPM with HSS (250 SFM) or up to 2,620 RPM with carbide (600 SFM), feeding about 0.0120 in/rev.
What tap uses a 7/8" drill?: 1"-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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