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A 5mm drill bit equals 0.1969 inches (5 ÷ 25.4 = 0.19685), and the nearest fractional size you’ll find in a standard American drill index is 13/64 inch (0.2031″) — about 0.006″ oversized. Whether that substitution works depends entirely on what goes into the hole, so here’s the full picture.
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The Exact Conversion
One inch is defined as exactly 25.4 millimeters, so converting any metric bit is a single division:
- Millimeters ÷ 25.4 = inches
- 5 ÷ 25.4 = 0.19685″ → rounds to 0.1969″ (machinists would call it “197 thou”)
That makes a 5mm bit just under one-fifth of an inch — noticeably fatter than a 3/16″ bit and visibly thinner than a 7/32″.
Closest Standard Sizes to 5mm
Three sizing systems matter here: fractional (what fills most US drill indexes), wire/number gauge, and metric. Here’s how the neighbors stack up:
| Bit size | Decimal inch | vs. 5mm (0.1969″) | Where you find it |
|---|---|---|---|
| 3/16″ | 0.1875 | −0.0094″ undersize | Every fractional set |
| #10 | 0.1935 | −0.0034″ | Number drill sets |
| #9 | 0.1960 | −0.0009″ — closest match | Number drill sets |
| 5mm | 0.1969 | — | Metric sets and singles |
| #8 | 0.1990 | +0.0021″ | Number drill sets |
| 13/64″ | 0.2031 | +0.0063″ | Fractional sets (1/64″ steps) |
| 7/32″ | 0.2188 | +0.0219″ | Every fractional set |
Two takeaways. First, the single closest standard bit to 5mm is actually a #9 wire-gauge drill (0.1960″) — off by less than a thousandth of an inch — but #9 only exists in numbered sets, which most woodshops don’t own. Second, the nearest fractional size is 13/64″, which is why it keeps getting recommended as the default substitute.
Will 13/64″ Work? It Depends on the Job
A 13/64″ hole is 0.0063″ wider than a true 5mm hole — a little more than the thickness of a sheet of printer paper. That gap is either irrelevant or a dealbreaker depending on the application.
Where 13/64″ is fine
- Clearance holes for M5 fasteners. Standard clearance for an M5 screw is actually 5.3–5.5mm anyway, so 13/64″ (5.16mm) gives a snug, tidy clearance fit.
- Through-holes where nothing indexes on diameter — wire pass-throughs, drainage holes, hanging hardware, rough work.
- Holes you’ll ream, sand, or fit with a bushing later, where starting slightly oversize costs nothing.
Where you need a true 5mm
- 5mm shelf pins. This is the big one for woodworkers — Euro-style cabinets and flat-pack furniture use 5mm pins. A 13/64″ hole leaves roughly 0.16mm of side play, so pins rattle and shelves rock under load. This is exactly why dedicated 5mm shelf-pin jig bits exist.
- 5mm dowels. Joinery depends on a line-to-line or slight interference fit; an oversized hole starves the glue joint of surface contact.
- Tap drilling for M6×1.0 threads. 5.0mm is the specified tap drill, giving roughly 80% thread engagement. A 13/64″ hole drops that to around 65–70% — it’ll tap, but threads strip more easily, especially in aluminum.
- Pilot holes sized to a screw chart. If the chart calls for 5mm, 13/64″ shaves holding power; in hardwoods a slightly undersize #9 or even 3/16″ usually performs better.
If You Need a Real 5mm Bit, What to Buy
- Brad-point for wood. Metric brad-point singles from brands like Fisch, Famag, or Freud run roughly $5–$15 each and leave clean, true-size holes for shelf pins and dowels.
- HSS jobber twist for mixed use. A single 5mm jobber from makers like Drill America, Bosch, or Milwaukee costs a few dollars; cobalt versions handle harder metals. Full metric sets (1–10mm in 0.5mm steps) run roughly $25–$60.
- Shelf-pin jig bits. Jigs from Kreg, Snappy, and similar makers ship with dedicated 5mm bits — a strong hint that fractional substitutes don’t cut it.
A few ownership realities: the outer spurs on a brad-point dull first, and once they do the bit starts cutting oversize — the very problem you bought it to avoid. Metric bits get lost inside fractional indexes, so store them separately or wrap the shank with colored tape. And at under 0.2″ diameter, a 5mm bit flexes easily in metal — use a center punch and moderate pressure. The most common mistake isn’t buying the wrong bit; it’s assuming 3/16″ is “basically 5mm” and discovering the dowel or pin won’t fit at all.
Why 5mm Trips People Up — Context Table
Here’s the part most conversion charts skip: 5mm is one of the worst metric sizes for fractional substitution. Its neighbors have near-perfect equivalents, which is why people assume 5mm does too:
| Metric bit | Decimal inch | Nearest fractional | Error |
|---|---|---|---|
| 3mm | 0.1181 | 1/8″ (0.1250) | +0.0069″ |
| 4mm | 0.1575 | 5/32″ (0.1563) | −0.0012″ — excellent |
| 5mm | 0.1969 | 13/64″ (0.2031) | +0.0063″ — poor |
| 6mm | 0.2362 | 15/64″ (0.2344) | −0.0018″ — excellent |
| 8mm | 0.3150 | 5/16″ (0.3125) | −0.0025″ — good |
| 10mm | 0.3937 | 25/64″ (0.3906) | −0.0031″ — good |
Five millimeters sits in a dead zone between fractional sizes — close to the midpoint of 3/16″ and 13/64″— while 4mm and 6mm almost land on exact fractions. If your project genuinely needs 5mm holes, buying the actual bit is money well spent.
FAQ
Is a 5mm bit the same as 3/16 inch?
No. 3/16″ equals 0.1875″ (4.76mm) — undersized by about 0.009″. A 5mm dowel, pin, or shaft won’t fit through a 3/16″ hole without sanding or re-drilling.
What’s the closest drill bit to 5mm overall?
A #9 wire-gauge bit (0.1960″), off by under a thousandth of an inch. If you own a numbered set, it’s effectively interchangeable. Otherwise 13/64″ is the closest fractional option.
Which is bigger, 5mm or 13/64″?
13/64″, by 0.0063″ (about 0.16mm).
Do typical hardware-store drill sets include 5mm?
Most fractional sets skip it entirely, jumping from 3/16″ to 13/64″. Buy a metric single, a 1–10mm metric index, or a combination set that includes metric sizes.