What is a 8.0 mm drill in decimal and mm?

0.3150 in, or 8.000 mm; nearest fractional drill: 5/16" (0.3125 in, -0.0025 in); nearest number / letter drill: Letter O (0.3160 in, +0.0010 in).

What RPM for a 8.0 mm drill in steel?

In low-carbon steel (1018) an HSS 8.0 mm drill (0.3150 in) runs about 1,090 RPM at 90 SFM; a carbide drill about 3,640 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 8.0 mm drill?

About 0.0081 in/rev in mild steel, 0.0073 in/rev in aluminum and 0.0053 in/rev in 304 stainless. At 1,090 RPM that is 8.83 IPM in steel (IPM = RPM × IPR).

What RPM for a 8.0 mm drill in aluminum?

3,030 RPM with HSS (250 SFM) or up to 7,280 RPM with carbide (600 SFM), feeding about 0.0073 in/rev.

What size is a 8.0 mm drill?

0.3150 in / 8.000 mm. The nearest other drills are Letter O (0.3160 in), 5/16" (0.3125 in), 7.9 mm (0.3110 in).

8.0 mm drill size

A 8.0 mm metric drill is 0.3150 in (8.000 mm).

Decimal inch: 0.3150
Millimeters: 8.000
Nearest 1/64: 5/16" (+0.0025)
Type: metric drill

Nearest equivalents in other systems

Drills closest to 8.0 mm
System	Drill	Inch	mm	Difference
Fractional	5/16"	0.3125	7.938	-0.0025 in
Number / letter	Letter O	0.3160	8.026	+0.0010 in

Speeds and feeds: in mild steel an HSS drill starts at about 1,090 RPM and 0.0081 in/rev (8.83 IPM); in 6061 aluminum about 3,030 RPM.

8.0 mm drill speeds and feeds by material

Jobber-length twist drill, D = 0.3150 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

8.0 mm drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	3,030	600	7,280	0.0073	22.1	53.1
Brass / free-machining	150	1,820	400	4,850	0.0058	10.6	28.1
Low-carbon steel (1018)	90	1,090	300	3,640	0.0081	8.83	29.5
Alloy steel (4140, annealed)	70	850	250	3,030	0.0086	7.31	26.1
Stainless 304	40	490	150	1,820	0.0053	2.60	9.65
Gray cast iron	80	970	250	3,030	0.0055	5.34	16.7
Titanium 6Al-4V	25	300	100	1,210	0.0036	1.08	4.36
Plastics (acetal)	300	3,640	500	6,060	0.0045	16.4	27.3

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 1,090 RPM × 0.206 mm/rev = 224 mm/min.

Worked example: 8.0 mm drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.3150 ≈ 1,090 RPM.
Feed for a 0.315 in drill in mild steel ≈ 0.0081 in/rev.
IPM = 1,090 × 0.0081 = 8.83 IPM.

Peck cycle by hole depth

8.0 mm drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 0.945 in (24 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 1.575 in (40 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 2.520 in (64 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 8.0 mm drill

No standard UNC, UNF or metric tap in our tables calls for a 8.0 mm drill. Use it for clearance, pilot or reamer prep holes.

Nearest drills

Letter O: 0.3160 in / 8.026 mm (+0.0010 in)
5/16": 0.3125 in / 7.938 mm (-0.0025 in)
7.9 mm: 0.3110 in / 7.900 mm (-0.0039 in)
8.1 mm: 0.3189 in / 8.100 mm (+0.0039 in)

Drill speed calculator, prefilled for 8.0 mm Drill finder: sizes near 8.0 mm Metric drill chart Decimal equivalent chart

Common questions

What is a 8.0 mm drill in decimal and mm?: 0.3150 in, or 8.000 mm; nearest fractional drill: 5/16" (0.3125 in, -0.0025 in); nearest number / letter drill: Letter O (0.3160 in, +0.0010 in).
What RPM for a 8.0 mm drill in steel?: In low-carbon steel (1018) an HSS 8.0 mm drill (0.3150 in) runs about 1,090 RPM at 90 SFM; a carbide drill about 3,640 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 8.0 mm drill?: About 0.0081 in/rev in mild steel, 0.0073 in/rev in aluminum and 0.0053 in/rev in 304 stainless. At 1,090 RPM that is 8.83 IPM in steel (IPM = RPM × IPR).
What RPM for a 8.0 mm drill in aluminum?: 3,030 RPM with HSS (250 SFM) or up to 7,280 RPM with carbide (600 SFM), feeding about 0.0073 in/rev.
What size is a 8.0 mm drill?: 0.3150 in / 8.000 mm. The nearest other drills are Letter O (0.3160 in), 5/16" (0.3125 in), 7.9 mm (0.3110 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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