6mm to Fraction Drill Bit Size Chart
A drawing, a foreign manual or a metric bit calls for six millimetres, and the index case in front of you is inch-only. No US fraction equals six, so the useful answer is which step sits closest above and which sits closest below.
What 6mm actually is
The step below and the step above miss six millimetres by very different amounts, so picking the wrong one is not a rounding quibble.
| What you asked for | US size | Inches | Millimetres | Gap from 6 mm |
|---|---|---|---|---|
| The size on your drawing | 6mm | 0.236220472 | 6.000 | reference |
| Nearest 1/64 step below | 15/64" | 0.234375 | 5.953 | -0.047 mm (-0.78%) |
| Nearest 1/64 step above | 1/4" | 0.25 | 6.350 | +0.350 mm (+5.83%) |
| Nearest number-letter size | B | 0.238 | 6.045 | +0.045 mm (+0.75%) |
| Next number-letter size down | A | 0.234 | 5.944 | -0.056 mm (-0.93%) |
Skip the step above when the hole has to stay near six millimetres, because it opens the hole a third of a millimetre where the step below costs only a twentieth. Six millimetres is neither a quarter inch nor three sixteenths. For a screw, a pin or a press fit, the number-letter sizes are the tighter bracket.
Find 6mm in the size finder — or read the full four-system chart, or every metric size in metric drill bit sizes.
How to read this chart
The conversion is arithmetic, not a lookup. An inch is defined as exactly twenty-five and four tenths of a millimetre, so every inch figure here is one exact division of the millimetre value by that same constant. The exact column keeps its trailing digits because they show how far a US step really sits from the size in your hand.
The gap is a signed millimetre difference, with the share of the metric size beside it. A negative gap leaves the hole undersize, a positive gap opens it oversize, and which way you go is a fit decision rather than a preference: take the step below for a clearance or slip fit, stay undersize for a pilot, let the finishing cut set the size on anything you will ream or counterbore, and on a fastener hole match the clearance the fastener needs rather than the nearest number on the lid.
A nearest-fraction cell is a shop approximation of a nominal designation, not a tolerance and not a measured value. Pick a candidate here, then gauge the hole before the fit matters.
Metric to US fraction table
Seventeen metric sizes with decimal inch, the nearest sixty-fourth of an inch step above and below, and the nearest number-letter size. This is the metric set these charts carry, not a complete standards series.
| Metric | Inch (dec) | Nearest 1/64 below | Gap mm | Nearest 1/64 above | Gap mm | Nearest number-letter | Gap mm | Find |
|---|---|---|---|---|---|---|---|---|
| 1mm | 0.0394 | 1/32" | -0.206 | 3/64" | +0.191 | #61 | -0.009 | Find → |
| 1.5mm | 0.0591 | 3/64" | -0.309 | 1/16" | +0.087 | #53 | +0.011 | Find → |
| 2mm | 0.0787 | 5/64" | -0.016 | 3/32" | +0.381 | #47 | -0.006 | Find → |
| 2.5mm | 0.0984 | 3/32" | -0.119 | 7/64" | +0.278 | #40 | -0.011 | Find → |
| 3mm | 0.1181 | 7/64" | -0.222 | 1/8" | +0.175 | #31 | +0.048 | Find → |
| 3.5mm | 0.1378 | 1/8" | -0.325 | 9/64" | +0.072 | #29 | -0.046 | Find → |
| 4mm | 0.1575 | 5/32" | -0.031 | 11/64" | +0.366 | #22 | -0.012 | Find → |
| 4.5mm | 0.1772 | 11/64" | -0.134 | 3/16" | +0.263 | #16 | -0.004 | Find → |
| 5mm | 0.1969 | 3/16" | -0.237 | 13/64" | +0.159 | #9 | -0.022 | Find → |
| 5.5mm | 0.2165 | 13/64" | -0.341 | 7/32" | +0.056 | #3 | -0.090 | Find → |
| 6mm | 0.2362 | 15/64" | -0.047 | 1/4" | +0.350 | B | +0.045 | Find → |
| 6.5mm | 0.2559 | 1/4" | -0.150 | 17/64" | +0.247 | F | +0.028 | Find → |
| 7mm | 0.2756 | 17/64" | -0.253 | 9/32" | +0.144 | J | +0.036 | Find → |
| 8mm | 0.3150 | 5/16" | -0.063 | 21/64" | +0.334 | O | +0.026 | Find → |
| 9mm | 0.3543 | 11/32" | -0.269 | 23/64" | +0.128 | T | +0.093 | Find → |
| 10mm | 0.3937 | 25/64" | -0.078 | 13/32" | +0.319 | X | +0.080 | Find → |
| 12mm | 0.4724 | 15/32" | -0.094 | 31/64" | +0.303 | — | — | Find → |
About nominal body diameter
Read this before you copy a number off the table.
Diameters on this page are the nominal BODY diameter of a standard twist drill. They are not a Forstner or wood-boring bit point diameter, not a step-drill tip diameter, and not a core-drill or hole-saw cut diameter.
Picking between the two neighbours
Both neighbours are wrong by a different amount, so the job decides which one you can live with. Four cases cover most of it:
- For a screw hole, match the clearance the fastener needs rather than the nearest number. A #12 clears the six millimetre hole with about half a millimetre to spare; the next size up, #14, is about a sixth of a millimetre wider than the hole and will not pass it.
- For a clearance or slip fit that has to slide, fifteen sixty-fourths leaves the hole a twentieth of a millimetre tight. That is small, but it is a press, not a slide.
- For a pilot hole, or anything you will ream or counterbore, either neighbour works, because the finishing cut sets the size.
- If the index case in front of you carries no six, buy the bit the hole is for instead of forcing the nearest label onto it. The two options miss by a twentieth of a millimetre and by a third of a millimetre, and that is not the same decision.
What these numbers are not
- Not a Forstner or wood-boring point diameter — a different series for the same hole.
- Not a step-drill tip diameter — a cutting-tip series, not a body series.
- Not a core-drill or hole-saw cut diameter — annular, measured at the cut.
- Not a spotting-drill point diameter — made smaller than the finished hole.
- Not a wire or cable diameter — a different measurement entirely.
Sources
Every number here comes from a published vendor table plus exact arithmetic, not from a standards body. Each source below is listed with what it was read for.
- Engineers Edge — the metric designation and its four-decimal inch value. A commercial publisher, not a standards body.
- ISO 10899:1996 — the definition of a drill diameter and the scope of a two-flute high-speed-steel twist drill. It delegates the diameter series to a dimensional standard whose table was not retrievable, so no number here is attributed to it.
- ASME B94.11M-1993 — the governing twist-drill standard and its inch and metric scope. Scope only.
- AmesWeb — the category scope of jobber twist drills. It supplies no number.
Related
Full drill bit size chart · Metric drill bit sizes · Fractional drill bit sizes · Number drill bit sizes · Letter drill bit sizes · Printable drill bit size chart · Drill bit size finder · Drill bits hub
FAQ
Is a 6mm drill bit the same as 3/16"?
No. Three sixteenths of an inch is just under four and three-quarter millimetres, so it lands more than a millimetre under six, about a fifth undersize. The nearest US step to six millimetres is fifteen sixty-fourths of an inch, which sits just under six, within five hundredths of a millimetre. If your drawing says six millimetres, drill six millimetres. If you are forced onto an inch-only index case, fifteen sixty-fourths is the closest option on it, not three sixteenths.
Is 6mm closer to 1/4 or 3/8"?
A quarter inch, by a wide margin. Six millimetres is a shade under fifteen sixty-fourths of an inch. A quarter inch is a third of a millimetre over, inside six percent. Three eighths is three and a half millimetres over, close to sixty percent. That puts a quarter inch roughly ten times closer to six millimetres than three eighths is. Neither is a substitute: six millimetres has no exact US fractional equivalent.
Is a 6mm drill bit 1/4"?
No, but a quarter inch is the closest common US size above six millimetres, a third of a millimetre larger. The closest US step below is fifteen sixty-fourths, just under six millimetres and inside one percent. So no US fraction equals six millimetres exactly — fifteen sixty-fourths is the nearest overall, and a quarter inch is the nearest of the sizes most US sets actually carry.
Is 5/32 a 6 mm drill bit?
No. Five thirty-seconds of an inch is just under four millimetres, so it is about two millimetres, or a third, smaller than six. The fractions near six millimetres are fifteen sixty-fourths below and a quarter inch above. In the US number-and-letter series the nearest members are A, just under six, and B, just over. They bracket six millimetres far more tightly than five thirty-seconds does.
Is 15/64" close enough to use instead of 6mm?
Only for some jobs, so check what the hole is for. Fifteen sixty-fourths sits just under six millimetres, inside one percent, which is close enough to matter. For a clearance or slip fit it leaves the hole slightly tight; for a fastener hole that can mean the fastener will not pass. For a pilot hole, or a hole you plan to ream or enlarge, it is a reasonable stand-in on an inch-only index. If your index carries no six, match the step to what the hole is for rather than to the nearest number on the label.