Number drill bit sizes
Wire-gauge style number sizes (#) — the labels stamped on many jobber sets between fractional steps. Each row lists the number label, decimal inch, and millimeter equivalent so you can match a tap chart or worn stamp without opening the full four-system chart. Need fractional, metric, or letter? Use the links below or the flagship chart.
Full size chart · Size finder · Drill hub · Fractional · Metric · Letter
How to use this table
Scan the Size column for the # mark on the bit or the number on a tap-drill chart. Decimal inch and mm are nominal workshop values for comparison — not lab certification. Click Find on a row to open the size finder with that label preselected. Shopping stays on the tool page.
Remember the gauge direction: larger number → smaller diameter (#52 is much smaller than #1). That trips people who treat “higher” as “bigger.” If a plan says #21 and your case only prints fractions, use decimal inch to find the nearest fractional neighbor, then decide whether nearest is good enough for the material.
Typical flow: read the number from the chart or stamp, find the row, cross-check mm if you hold a metric bit box, then Find → size finder. Critical tap and reamer work still needs the bit and a gauge — do not treat the table as a guarantee.
Drill bit set (nearest shop staple)
Number gauges are rarely printed on consumer set lids. One optional fractional set covers common pilots nearby — use Find on a row for label-honest matching in the size finder.
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FAQ
What are number drill bit sizes?
Number sizes use a wire-gauge style label such as #7 or #21. Higher numbers are smaller diameters. They sit between fractional steps for tighter pilot and tap-drill work.
Which number sizes are on this page?
This table lists 8 common shop sizes (#1, #7, #10, #21, #29, #36, #43, #52). It is not every #1–#80 gauge — open the full chart if you need a neighboring system, or match decimal inch to the nearest fractional bit you already own.
How do number sizes relate to fractional bits?
Number sizes fill gaps between fractions. Example: #7 is about 0.2010" (near 13/64"), useful when 3/16" is small and 1/4" is large. Use the decimal and mm columns to compare.
Where do I shop a set that includes a number size?
Click Find on a row to open the size finder with that label. Many consumer sets print only fractional lids; if the set does not list your # size, the finder says so instead of claiming a match.
Sources
Number diameters follow common published wire-gauge drill indexes. Values are nominal. Confirm critical fits on the bit or with a gauge.
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