What size is a 47/64" drill bit?

A 47/64" drill bit is 0.7344 in in diameter, which is 18.653 mm. It is the 47/64 in fractional size.

What is the metric equivalent of a 47/64" drill bit?

The closest metric drill to a 47/64" drill bit (18.653 mm) is 18.75 mm, which is 18.750 mm — 0.0038 in larger.

Fractional drill · 47/64

47/64" Drill Bit Size — Decimal Inch, Millimetre and Tap Sizes

https://shopmath.org/drills/fractional/47-64 · data verified August 1, 2026

A 47/64" drill bit is 0.7344 in (18.653 mm) in diameter. Diameters are nominal.

Series: Fractional
Designation: 47/64
Inch: 0.7344
mm: 18.653
Standard: ANSI/ASME B94.11M

Fractional Drill · 47/64 · nominal diameter

0.7344 in

Millimetre: 18.653mm
Fraction: 47/64in

Nominal diameter. A worn or run-out drill cuts oversize, which leaves less thread in a tapped hole than the table says.

47/64" Drill Bit Size in Inches and Millimetres

The nominal diameter of a 47/64" drill bit. Drill sizes are nominal — a worn drill, run-out or a soft material that closes in behind the cut all move the finished hole.

47/64" drill bit — decimal inch and millimetre diameter
Property	Value
Diameter, decimal inch	0.7344 in
Diameter, millimetre	18.653 mm
Fraction	47/64 in
Cross-sectional area	0.42357 in²

1 in = 25.4 mm exactly, so the two columns are the same value in different units, not two measurements.

47/64" Drill Bit Equivalents in Every Other Drill Series

The closest size to the 47/64" drill bit in each of the other three indexes, with the difference in inches. None of them is the same drill — check the difference before substituting one into a tapped hole.

Nearest number, letter, fractional and metric equivalents to a 47/64" drill bit
Property	Property	Diameter		Property
Drill	Series	in	mm	Difference, in
#1	Number	0.2280	5.791	−0.5064
Z	Letter	0.4130	10.490	−0.3214
18.75 mm	Metric	0.7382	18.750	+0.0038

A positive difference means the equivalent drill is larger, which leaves less thread in a tapped hole. Sizes without a link are stored for the nearest-drill calculation but do not carry their own page.

Drill Sizes Either Side of the 47/64" Drill Bit

Ordered by diameter across all four indexes, so the next size up may be a letter, a fraction or a metric drill rather than the next one in this series.

Standard drill sizes adjacent to a 47/64" drill bit, by diameter
Property	Property	Diameter
Drill	Series	in	mm
23/32"	Fractional	0.7188	18.256
18.5 mm	Metric	0.7283	18.500
47/64"	Fractional	0.7344	18.653
18.75 mm	Metric	0.7382	18.750
19 mm	Metric	0.7480	19.000

Sources and Method for the 47/64" Drill Bit Size

Drill diametercomputed

Number/letter: bd_warehouse drill_sizes.csv (Apache-2.0) cross-checked against Wikipedia Drill bit sizes (CC BY-SA 4.0). Fractional: computed 1/64 in steps per ANSI B94.11M. Metric: computed BS 328 increment pattern.

Verified against Wikipedia Drill bit sizes (CC BY-SA 4.0); 31/31 checks passed

Computed from the standard's formulas, then checked against published tables.

Formula

Fractional drill diameter

Ø  =  47/64 in  =  0.7344 in

Fractional drills are exact fractions of an inch in 1/64 in steps; the decimal is the fraction evaluated, not a measurement.

Assumptions

Diameters are nominal. Drill manufacturing tolerance, wear and run-out all cut oversize, and every one of those moves a tapped hole toward less thread than the table says.
Dataset scope: Number sizes #61-#80 are stored but tagged demandTier 'extended' — query-space-map.md Appendix A found the tail thinning in the 60s. Sizes below #80 and metric sizes above 25.0 mm excluded.

Data last verified

August 1, 2026

How this data is built and checked →

How to Cite This 47/64" Drill Bit Reference

Citation

ShopMath. "47/64" Drill Bit Size — Decimal Inch, Millimetre and Tap Sizes." ShopMath, verified August 1, 2026, https://shopmath.org/drills/fractional/47-64

BibTeX

@misc{shopmath-drills-fractional-47-64,
  title        = {47/64" Drill Bit Size — Decimal Inch, Millimetre and Tap Sizes},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/drills/fractional/47-64}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/drills/fractional/47-64

Common Questions About the 47/64" Drill Bit

What size is a 47/64" drill bit?: A 47/64" drill bit is 0.7344 in in diameter, which is 18.653 mm. It is the 47/64 in fractional size.
What is the metric equivalent of a 47/64" drill bit?: The closest metric drill to a 47/64" drill bit (18.653 mm) is 18.75 mm, which is 18.750 mm — 0.0038 in larger.

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