Drill Bit Size Chart
Four common size systems in one reference table: fractional inch, metric millimeters, number (#), and letter (A–Z). Each row shows the shop label plus decimal-inch and mm so you can compare systems without flipping between catalogs. Shopping stays on the size finder — this page is for lookup and cross-check, not a product wall.
Fractional sizes
Inch fractions such as 1/4" and 3/8".
| Size | Inch (dec) | mm | Look up |
|---|---|---|---|
| 1/64" | 0.0156 | 0.40 | Find → |
| 1/32" | 0.0312 | 0.79 | Find → |
| 3/64" | 0.0469 | 1.19 | Find → |
| 1/16" | 0.0625 | 1.59 | Find → |
| 5/64" | 0.0781 | 1.98 | Find → |
| 3/32" | 0.0938 | 2.38 | Find → |
| 7/64" | 0.1094 | 2.78 | Find → |
| 1/8" | 0.1250 | 3.17 | Find → |
| 9/64" | 0.1406 | 3.57 | Find → |
| 5/32" | 0.1562 | 3.97 | Find → |
| 11/64" | 0.1719 | 4.37 | Find → |
| 3/16" | 0.1875 | 4.76 | Find → |
| 13/64" | 0.2031 | 5.16 | Find → |
| 7/32" | 0.2188 | 5.56 | Find → |
| 15/64" | 0.2344 | 5.95 | Find → |
| 1/4" | 0.2500 | 6.35 | Find → |
| 17/64" | 0.2656 | 6.75 | Find → |
| 9/32" | 0.2812 | 7.14 | Find → |
| 5/16" | 0.3125 | 7.94 | Find → |
| 11/32" | 0.3438 | 8.73 | Find → |
| 3/8" | 0.3750 | 9.52 | Find → |
| 13/32" | 0.4062 | 10.32 | Find → |
| 7/16" | 0.4375 | 11.11 | Find → |
| 15/32" | 0.4688 | 11.91 | Find → |
| 1/2" | 0.5000 | 12.70 | Find → |
| 9/16" | 0.5625 | 14.29 | Find → |
| 5/8" | 0.6250 | 15.88 | Find → |
| 11/16" | 0.6875 | 17.46 | Find → |
| 3/4" | 0.7500 | 19.05 | Find → |
| 13/16" | 0.8125 | 20.64 | Find → |
| 7/8" | 0.8750 | 22.22 | Find → |
| 15/16" | 0.9375 | 23.81 | Find → |
| 1" | 1.0000 | 25.40 | Find → |
Full fractional series: open split page .
Metric sizes
Millimeters such as 3mm and 6.5mm.
| Size | Inch (dec) | mm | Look up |
|---|---|---|---|
| 1mm | 0.0394 | 1.00 | Find → |
| 1.5mm | 0.0591 | 1.50 | Find → |
| 2mm | 0.0787 | 2.00 | Find → |
| 2.5mm | 0.0984 | 2.50 | Find → |
| 3mm | 0.1181 | 3.00 | Find → |
| 3.5mm | 0.1378 | 3.50 | Find → |
| 4mm | 0.1575 | 4.00 | Find → |
| 4.5mm | 0.1772 | 4.50 | Find → |
| 5mm | 0.1969 | 5.00 | Find → |
| 5.5mm | 0.2165 | 5.50 | Find → |
| 6mm | 0.2362 | 6.00 | Find → |
| 6.5mm | 0.2559 | 6.50 | Find → |
| 7mm | 0.2756 | 7.00 | Find → |
| 8mm | 0.3150 | 8.00 | Find → |
| 9mm | 0.3543 | 9.00 | Find → |
| 10mm | 0.3937 | 10.00 | Find → |
| 12mm | 0.4724 | 12.00 | Find → |
Full metric series: open split page .
Number sizes
Number sizes such as #7 and #21.
Full number series: open split page .
Letter sizes
Letter sizes A–Z.
Full letter series: open split page .
How to read this chart
Start with the system your drawing or bit set already uses. Fractional labels look like 1/4" and match most consumer index cases. Metric labels are millimeters (for example 6mm). Number sizes use a hash prefix (#7, #21). Letter sizes run A through Z. The Size column is the label you match on the shank, the case, or the Amazon kit title — not a brand SKU.
Decimal inch and mm sit beside each label so you can cross-walk systems. If a plan calls for 6mm and your set is fractional only, scan the fractional block for the nearest decimal or open the finder to compare. Values are workshop-grade equivalents; they are not a substitute for a pin gauge when a press fit or bearing bore is critical.
Use Find on a row to open the size finder with that label preselected. The finder is the money path: confirm the label, then a single kit card when the size is mapped. Prefer mapped fractional shop staples (1/16" through 1/2") when you want a set that honestly lists the size. Number, letter, and metric labels still look up correctly on the chart even when a kit map falls back to a default fractional set.
- Size — label printed on the bit or in the set index.
- Inch (dec) — decimal inch for quick comparison.
- mm — millimeter equivalent for metric drawings and bits.
- Find — deep-links to the finder with
?label=.
When to leave this chart
Need one series only? Open a split page (fractional, metric, number, or letter) for a quieter table. Already know the label and want a set? Skip straight to the size finder . Matching a screw to a pilot or clearance hole is a different job — use the screw→drill tool when that ships for your fastener, not this diameter chart alone.
FAQ
What is the difference between fractional and number drill bits?
Fractional bits use inch fractions such as 1/4". Number bits use the #1–#80 series with finer steps, often for small holes and tap drill work. Compare both with the decimal-inch and mm columns on this chart.
How do I convert a drill bit size to millimeters?
Read the mm column on the same row, or open the size finder with that label. Millimeters here are nominal equivalents for shop comparison, not a claim of metrology-lab precision.
How do I use this chart with the size finder tool?
Click Find on any row, or use Find your size above. The finder opens with that label preselected so you can confirm decimal/mm and see a kit that lists the size when the label is mapped.
Is this an official engineering chart?
No. It is a workshop reference built from common published size systems. Confirm critical fits on the bit shank or manufacturer table. See the site disclaimer for limits of use.
Which drill bit sizes are best for a starter set?
Most home shops start with common fractionals: 1/16", 1/8", 3/16", 1/4", 3/8", and 1/2". Use Find on those rows to open the finder and a set that includes the label. Number and letter sizes matter more once you tap or match odd pilots.
Why do number and letter sizes exist if fractions already cover inches?
Fractions jump in coarse steps. Number and letter series fill gaps used by taps, rivets, and older machinery drawings. When a fraction is slightly large or small for the hole you need, check the nearest number or letter row.
Sources
Fractional and metric series follow common published size progressions used in consumer and
trade drill indexes. Number and letter diameters follow standard number/letter drill tables
(decimal inch) with millimeter columns as inch×25.4 rounded for shop use. Dual-sourced and
marked status=ok in site data. Always confirm critical fits against the bit
manufacturer or a gauge — this page is a workshop reference, not a certified engineering
standard.