What are number (wire gauge) drill sizes?

Numbered drill sizes (#80 to #1) are a wire gauge series commonly used in North America for small holes. #80 is the smallest and #1 is the largest in that series.

What are letter drill sizes?

Letter drills run from A (smallest) to Z (largest) and fill diameter gaps between fractional sizes.

How do I convert mm to the nearest inch drill size?

Use the converter on this page to enter your mm value; it shows the decimal inch and highlights the nearest fractional, number, or letter size in the chart.

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Decimal Equivalents of Fractional, Wire and Letter Drill Sizes

This chart lists fractional inch drills, number (wire gauge) drills #80 to #1, and letter drills A to Z alongside their decimal inch values. Use the quick finder to jump to any size or the converter to input fraction / # / letter / inch / mm and highlight the nearest size in the table.

Jump to size or value

Accepts fraction, #wire (e.g., #40 or 40), letter (A–Z), decimal inch, or mm (add “mm”).

Quick Converter & Nearest Drill Size

Enter value

Inches (decimal)	—
Millimeters	—
Nearest drill size	—

Nearest is based on absolute difference in decimal inches parsed from the chart below.

Decimal Equivalents — Fractional, Wire (#), and Letter (A–Z)
Size	Decimal (in)	Size	Decimal (in)	Size	Decimal (in)	Size	Decimal (in)

Tip: Headers stick while you scroll; use the finder to highlight the matching pair.

How to Use the Chart

Fractional: Enter a fraction like 7/32 or a decimal like 0.2188.
Wire (#): Type #40 or just 40 to jump to number drills.
Letter: Enter a letter Q, Z, etc.
Metric: Append mm (e.g., 6.5 mm) and the converter finds the nearest inch size.

Reference

ASME B94.33-1996 — Jig Bushings (Inch Series)