What size is a Number 21 drill bit? (#21 drill bit size)

What size is a #21 drill bit?

Numbered drill bit gauge sizes range in ascending order from 80 (smallest) to 1 (largest). Thus, drill bit #21 is in the middle of your standard drill set. Here we will give you drill bit #21 in decimal inches, drill bit #21 in fractional inches, and drill bit #21 in decimal millimeters (mm).

The purpose of this page is to give you an alternate drill bit (approximate equivalent) to drill bit gauge size Number 21 (#21).

We start by displaying drill bit Number 21 in decimal inches as follows:

#21 drill bit = 0.1590 inches

0.1590 decimal as a fraction is 159/1000. However, standard fractional drill bits come in intervals of 1/64 inches. Therefore, there are no standard fractional drill bits that are the exact 159/1000 fraction that the #21 drill bit is. To find the closest gauge wire #21 drill bit equivalent in fractional inches, we round 159/1000 up and down to 1/64 accuracy to get the following:

≈ 5/32 inches rounded down
#21 drill bit = 159/1000 inches
≈ 11/64 inches rounded up

Caution: Due to rounding, a 5/32 drill bit will make the hole smaller than a #21 drill bit and a 11/64 drill bit will make the hole larger than a #21 drill bit. Below we converted the fractions to decimals so you can compare more easily:

5/32 = 0.15625 inches
#21 = 0.1590 inches
11/64 = 0.171875 inches

There are 25.4 millimeters (mm) in an inch. Thus, to convert a #21 drill bit to millimeters, you simply multiply the decimal inches by 25.4 like so:

0.1590 inches x 25.4
= 4.0386 mm

Drill Bit Size Chart
For additional information about what drill bit to use, you may also want to take a look at the Drill Bit Size Chart which includes fractional inch drill bits, gauge wire drill bits, and metric drill bits sorted by size.

Gauge Number Drill Bit Size
Submit another drill bit gauge size below for us to size for you.

What size is a Number 22 drill bit?
Here is another drill bit you may be interested in learning about.