Drill Bit Size Chart: Bit Sizes & Diameters
Look up drill bit sizes with numeric, letter, and fractional drills. Drill diameter in millimeters and inches for CNC programming, drill charts, and tap drill selection.
Find drill bit size by diameter
Enter a target hole diameter in mm or inches to find the nearest standard number, letter, or fractional drill.
| Size | Diameter (mm) | Diameter (in) | Category |
|---|---|---|---|
| #80 | 0.34 mm | 0.0135″ | Numeric |
| #79 | 0.37 mm | 0.0145″ | Numeric |
| 1/64 | 0.40 mm | 0.0156″ | Fractional |
| #78 | 0.41 mm | 0.016″ | Numeric |
| #77 | 0.46 mm | 0.018″ | Numeric |
| #76 | 0.51 mm | 0.02″ | Numeric |
| #75 | 0.53 mm | 0.021″ | Numeric |
| #74 | 0.57 mm | 0.0225″ | Numeric |
| #73 | 0.61 mm | 0.024″ | Numeric |
| #72 | 0.64 mm | 0.025″ | Numeric |
| #71 | 0.66 mm | 0.026″ | Numeric |
| #70 | 0.71 mm | 0.028″ | Numeric |
| #69 | 0.74 mm | 0.0292″ | Numeric |
| #68 | 0.79 mm | 0.031″ | Numeric |
| 2/64 | 0.79 mm | 0.0313″ | Fractional |
| #67 | 0.81 mm | 0.032″ | Numeric |
| #66 | 0.84 mm | 0.033″ | Numeric |
| #65 | 0.89 mm | 0.035″ | Numeric |
| #64 | 0.91 mm | 0.036″ | Numeric |
| #63 | 0.94 mm | 0.037″ | Numeric |
| #62 | 0.97 mm | 0.038″ | Numeric |
| #61 | 0.99 mm | 0.039″ | Numeric |
| #60 | 1.02 mm | 0.04″ | Numeric |
| #59 | 1.04 mm | 0.041″ | Numeric |
| #58 | 1.07 mm | 0.042″ | Numeric |
| #57 | 1.09 mm | 0.043″ | Numeric |
| #56 | 1.18 mm | 0.0465″ | Numeric |
| 3/64 | 1.19 mm | 0.0469″ | Fractional |
| #55 | 1.32 mm | 0.052″ | Numeric |
| #54 | 1.40 mm | 0.055″ | Numeric |
| #53 | 1.51 mm | 0.0595″ | Numeric |
| 4/64 | 1.59 mm | 0.0625″ | Fractional |
| #52 | 1.61 mm | 0.0635″ | Numeric |
| #51 | 1.70 mm | 0.067″ | Numeric |
| #50 | 1.78 mm | 0.07″ | Numeric |
| #49 | 1.85 mm | 0.073″ | Numeric |
| #48 | 1.93 mm | 0.076″ | Numeric |
| 5/64 | 1.98 mm | 0.0781″ | Fractional |
| #47 | 1.99 mm | 0.0785″ | Numeric |
| #46 | 2.06 mm | 0.081″ | Numeric |
| #45 | 2.08 mm | 0.082″ | Numeric |
| #44 | 2.18 mm | 0.086″ | Numeric |
| #43 | 2.26 mm | 0.089″ | Numeric |
| #42 | 2.37 mm | 0.0935″ | Numeric |
| 6/64 | 2.38 mm | 0.0938″ | Fractional |
| #41 | 2.44 mm | 0.096″ | Numeric |
| #40 | 2.49 mm | 0.098″ | Numeric |
| #39 | 2.53 mm | 0.0995″ | Numeric |
| #38 | 2.58 mm | 0.1015″ | Numeric |
| #37 | 2.64 mm | 0.104″ | Numeric |
| #36 | 2.71 mm | 0.1065″ | Numeric |
| 7/64 | 2.78 mm | 0.1094″ | Fractional |
| #35 | 2.79 mm | 0.11″ | Numeric |
| #34 | 2.82 mm | 0.111″ | Numeric |
| #33 | 2.87 mm | 0.113″ | Numeric |
| #32 | 2.95 mm | 0.116″ | Numeric |
| #31 | 3.05 mm | 0.12″ | Numeric |
| 8/64 | 3.17 mm | 0.125″ | Fractional |
| #30 | 3.26 mm | 0.1285″ | Numeric |
| #29 | 3.45 mm | 0.136″ | Numeric |
| #28 | 3.57 mm | 0.1405″ | Numeric |
| 9/64 | 3.57 mm | 0.1406″ | Fractional |
| #27 | 3.66 mm | 0.144″ | Numeric |
| #26 | 3.73 mm | 0.147″ | Numeric |
| #25 | 3.80 mm | 0.1495″ | Numeric |
| #24 | 3.86 mm | 0.152″ | Numeric |
| #23 | 3.91 mm | 0.154″ | Numeric |
| 10/64 | 3.97 mm | 0.1563″ | Fractional |
| #22 | 3.99 mm | 0.157″ | Numeric |
| #21 | 4.04 mm | 0.159″ | Numeric |
| #20 | 4.09 mm | 0.161″ | Numeric |
| #19 | 4.22 mm | 0.166″ | Numeric |
| #18 | 4.31 mm | 0.1695″ | Numeric |
| 11/64 | 4.37 mm | 0.1719″ | Fractional |
| #17 | 4.39 mm | 0.173″ | Numeric |
| #16 | 4.50 mm | 0.177″ | Numeric |
| #15 | 4.57 mm | 0.18″ | Numeric |
| #14 | 4.62 mm | 0.182″ | Numeric |
| #13 | 4.70 mm | 0.185″ | Numeric |
| 12/64 | 4.76 mm | 0.1875″ | Fractional |
| #12 | 4.80 mm | 0.189″ | Numeric |
| #11 | 4.85 mm | 0.191″ | Numeric |
| #10 | 4.91 mm | 0.1935″ | Numeric |
| #9 | 4.98 mm | 0.196″ | Numeric |
| #8 | 5.05 mm | 0.199″ | Numeric |
| #7 | 5.11 mm | 0.201″ | Numeric |
| 13/64 | 5.16 mm | 0.2031″ | Fractional |
| #6 | 5.18 mm | 0.204″ | Numeric |
| #5 | 5.22 mm | 0.2055″ | Numeric |
| #4 | 5.31 mm | 0.209″ | Numeric |
| #3 | 5.41 mm | 0.213″ | Numeric |
| 14/64 | 5.56 mm | 0.2188″ | Fractional |
| #2 | 5.61 mm | 0.221″ | Numeric |
| #1 | 5.79 mm | 0.228″ | Numeric |
| A | 5.94 mm | 0.234″ | Letter |
| 15/64 | 5.95 mm | 0.2344″ | Fractional |
| B | 6.05 mm | 0.238″ | Letter |
| C | 6.15 mm | 0.242″ | Letter |
| D | 6.25 mm | 0.246″ | Letter |
| E | 6.35 mm | 0.25″ | Letter |
| 16/64 | 6.35 mm | 0.25″ | Fractional |
| F | 6.53 mm | 0.257″ | Letter |
| G | 6.63 mm | 0.261″ | Letter |
| 17/64 | 6.75 mm | 0.2656″ | Fractional |
| H | 6.76 mm | 0.266″ | Letter |
| I | 6.91 mm | 0.272″ | Letter |
| J | 7.04 mm | 0.277″ | Letter |
| K | 7.14 mm | 0.281″ | Letter |
| 18/64 | 7.14 mm | 0.2813″ | Fractional |
| L | 7.37 mm | 0.29″ | Letter |
| M | 7.49 mm | 0.295″ | Letter |
| 19/64 | 7.54 mm | 0.2969″ | Fractional |
| N | 7.67 mm | 0.302″ | Letter |
| 20/64 | 7.94 mm | 0.3125″ | Fractional |
| O | 8.03 mm | 0.316″ | Letter |
| P | 8.20 mm | 0.323″ | Letter |
| 21/64 | 8.33 mm | 0.3281″ | Fractional |
| Q | 8.43 mm | 0.332″ | Letter |
| R | 8.61 mm | 0.339″ | Letter |
| 22/64 | 8.73 mm | 0.3438″ | Fractional |
| S | 8.84 mm | 0.348″ | Letter |
| T | 9.09 mm | 0.358″ | Letter |
| 23/64 | 9.13 mm | 0.3594″ | Fractional |
| U | 9.35 mm | 0.368″ | Letter |
| 24/64 | 9.52 mm | 0.375″ | Fractional |
| V | 9.58 mm | 0.377″ | Letter |
| W | 9.80 mm | 0.386″ | Letter |
| 25/64 | 9.92 mm | 0.3906″ | Fractional |
| X | 10.08 mm | 0.397″ | Letter |
| Y | 10.26 mm | 0.404″ | Letter |
| 26/64 | 10.32 mm | 0.4063″ | Fractional |
| Z | 10.49 mm | 0.413″ | Letter |
| 27/64 | 10.72 mm | 0.4219″ | Fractional |
| 28/64 | 11.11 mm | 0.4375″ | Fractional |
| 29/64 | 11.51 mm | 0.4531″ | Fractional |
| 30/64 | 11.91 mm | 0.4688″ | Fractional |
| 31/64 | 12.30 mm | 0.4844″ | Fractional |
| 32/64 | 12.70 mm | 0.5″ | Fractional |
| 33/64 | 13.10 mm | 0.5156″ | Fractional |
| 34/64 | 13.49 mm | 0.5313″ | Fractional |
| 35/64 | 13.89 mm | 0.5469″ | Fractional |
| 36/64 | 14.29 mm | 0.5625″ | Fractional |
| 37/64 | 14.68 mm | 0.5781″ | Fractional |
| 38/64 | 15.08 mm | 0.5938″ | Fractional |
| 39/64 | 15.48 mm | 0.6094″ | Fractional |
| 40/64 | 15.88 mm | 0.625″ | Fractional |
| 41/64 | 16.27 mm | 0.6406″ | Fractional |
| 42/64 | 16.67 mm | 0.6563″ | Fractional |
| 43/64 | 17.07 mm | 0.6719″ | Fractional |
| 44/64 | 17.46 mm | 0.6875″ | Fractional |
| 45/64 | 17.86 mm | 0.7031″ | Fractional |
| 46/64 | 18.26 mm | 0.7188″ | Fractional |
| 47/64 | 18.65 mm | 0.7344″ | Fractional |
| 48/64 | 19.05 mm | 0.75″ | Fractional |
| 49/64 | 19.45 mm | 0.7656″ | Fractional |
| 50/64 | 19.84 mm | 0.7813″ | Fractional |
| 51/64 | 20.24 mm | 0.7969″ | Fractional |
| 52/64 | 20.64 mm | 0.8125″ | Fractional |
| 53/64 | 21.03 mm | 0.8281″ | Fractional |
| 54/64 | 21.43 mm | 0.8438″ | Fractional |
| 55/64 | 21.83 mm | 0.8594″ | Fractional |
| 56/64 | 22.22 mm | 0.875″ | Fractional |
| 57/64 | 22.62 mm | 0.8906″ | Fractional |
| 58/64 | 23.02 mm | 0.9063″ | Fractional |
| 59/64 | 23.42 mm | 0.9219″ | Fractional |
| 60/64 | 23.81 mm | 0.9375″ | Fractional |
| 61/64 | 24.21 mm | 0.9531″ | Fractional |
| 62/64 | 24.61 mm | 0.9688″ | Fractional |
| 63/64 | 25.00 mm | 0.9844″ | Fractional |
| 1 | 25.40 mm | 1″ | Fractional |
Quick answer: what drill bit size do I need?
Drill bits use three naming systems: number (#80–#1), letter (A–Z), and fractional inch sizes. Search the table by name (#7, 1/4″) or use the diameter lookup above to find the nearest standard drill.
PREMSA's chart lists 170 ASME B94.11M sizes with drill diameter in mm and inches on every row — number, letter, and fractional series in one place.
For threaded holes, the pre-tap drill must be smaller than the finished thread. Cross-check with our Tap Drill Size Calculator, not the bolt clearance diameter.
Common sizes: #7 → 0.201″ (5.11 mm) · Letter A → 0.234″ (5.94 mm) · #29 → 0.136″ (3.45 mm)
Drill bit size chart: number, letter, fractional & tap drill reference
How drill size charts work
Machinists search drill bit size chart, drill size chart, and drill diameter chart thousands of times per month — usually to match a print callout, pick a tap drill, or program a CNC tool list. A reliable chart prevents costly mistakes: wrong drill diameter overloads taps, weakens threads, and breaks CAM prove-out cycles.
PREMSA's drill size chart lists 170 standard drill sizes — number drills (#80–#1), letter drills (A–Z), and fractional drills (1/64″–1″) — with drill diameter in mm and inches on every row.
Whether you need a wire drill size chart, a tap drill size chart cross-reference, or a quick #29 drill size lookup, filter the table above or use the diameter search tool.
Drill series in this drill bit size chart
- Number (#80–#1) — Wire drills — higher # = smaller diameter. Includes #29 (0.1360″ / 3.454 mm), #7 (0.2010″ / 5.105 mm), #43 (0.0890″ / 2.261 mm).
- Letter (A–Z) — 26 mid-range sizes between fractional and number drills.
- Fractional (1/64″–1″) — Standard inch fractions — 1/8″ (3.175 mm), 1/4″ (6.350 mm), 3/8″, 1/2″, and up to 1″.
- Mm and inches — Both columns on every row; convert manually with × 25.4 or use the diameter lookup.
Why machinists use a standard drill size chart
CNC posts, presetters, and inspection reports assume recognized drill names — not arbitrary decimals.
Accurate drill selection from a drill bit size chart affects tap drill quality, reamer and bore fit, tool life, first-article inspection, and communication between design, CAM, and the shop floor.
Keeping number, letter, and fractional drill sizes in one drill size chart cuts back-and-forth when a drawing calls out a wire size and programming needs the metric equivalent.
Using this chart and diameter lookup
Filter by Numeric, Letter, Fractional, or All. Each row shows size name, drill diameter in mm and in, and category — ready to cross-check with our Tap Drill Size Calculator.
Engineers and machinists use this drill bit size chart to look up #29, #7, 1/4″, and 1/8″; convert drill diameter between mm and inches during CAM programming; build CNC tool libraries; and quote drilling, reaming, and tapping operations.
For threaded holes, pair this drill size chart with our Tap Drill Size Calculator. For hole and thread DFM, see the CNC Design Guide.
Popular drill size chart searches
Direct answers to the drill bit lookups machinists and engineers search most often:
- What size is a #29 drill bit?
- #29 drill size = 0.1360 inches = 3.454 mm. One of the most referenced sizes in tap drill tables and wire drill charts.
- 1/4 inch drill bit size in mm
- 1/4″ fractional drill = 0.2500″ = 6.350 mm. Filter Fractional in the table above.
- 1/8 drill bit size in mm
- 1/8″ drill = 0.1250″ = 3.175 mm. A standard fractional size in every drill size chart.
- Wire drill size chart
- Wire drills are number drills (#80–#1). Filter Numeric in the table — #80 (~0.0135″) is the smallest standard number drill.
- Number vs letter vs fractional drill
- Number (#80–#1): fine wire sizes, higher # = smaller. Letter (A–Z): mid range. Fractional: 1/64″ steps in inches. All three appear in standard drill bit size charts.
- Drill bit size chart mm and inches
- Every row shows Diameter (mm) and Diameter (in). Multiply inches × 25.4 to convert, or use the diameter lookup above.
- Tap drill size chart
- A tap drill chart lists the hole diameter before tapping — smaller than the finished thread. Cross-reference with our Tap Drill Size Calculator, not bolt clearance diameter.
- What size is a #7 drill bit?
- #7 drill size = 0.2010″ = 5.105 mm. Common pre-tap size for 1/4-20 UNC threads in shop practice.
- Smallest number drill size
- #80 is the smallest standard number drill at ~0.0135″ (~0.343 mm).
- Standard drill sizes chart
- This page lists 170 standard drill sizes per ASME B94.11M — full number, letter, and fractional series with mm and inch diameters.
How to use this drill size chart
- PREMSA publishes this drill bit size chart with 170 standard drill sizes: 80 number drills (#80–#1), 26 letter drills (A–Z), and 64 fractional drills (1/64″–1″)—each row shows drill diameter in mm and inches.
- In the number drill series, a higher # means a smaller diameter: #80 ≈ 0.0135″ (0.343 mm) is the smallest; #1 ≈ 0.228″ (5.791 mm) is the largest. #29 = 0.1360″ (3.454 mm) is one of the most referenced tap-drill sizes in shop practice.
- Letter drills (A–Z) and fractional drills (1/64″ steps) cover diameters the number series does not. To convert inches to mm, multiply by 25.4—or read the Diameter (mm) column or use the diameter lookup above.
- For tap drill selection, the pre-tap hole must be smaller than the finished thread—not the bolt clearance diameter. Confirm with PREMSA's Tap Drill Size Calculator before CAM programming or tool ordering.
- Values are nominal catalog diameters (ASME B94.11M). Measure worn tools or verify on scrap for tight fits. For production drilling and threading at PREMSA in Monterrey, request a CNC quote with your STEP file and drawing.
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Drill size chart questions
- What is a number drill in a drill size chart?
- A number drill uses the # series from #80 (smallest, about 0.0135″) to #1 (largest, about 0.228″). Number drills fill gaps between fractional sizes and appear in standard drill size charts and tap drill tables.
- What is the difference between letter and number drill bits?
- Letter drills (A–Z) cover mid-range diameters when a fractional size is too small. Number drills extend finer and coarser. Both are listed in this drill bit size chart with drill diameter in mm and inches.
- How do I read drill diameter in millimeters?
- Multiply the decimal inch value by 25.4, or use the Diameter (mm) column in this drill size chart directly—no manual conversion needed during programming or inspection.
- Which drill size do I use before tapping?
- Use a tap drill chart or calculator, not the bolt clearance size. The correct pre-tap hole depends on thread series, pitch, and tap type. See our Tap Drill Size Calculator.
- Are fractional drills the same as number drills?
- No. Fractional drills use common inch fractions (1/64, 1/32, etc.). Number and letter drills use separate naming systems. Shops reference all three in one drill size chart.
- Why does my drill measure different from the chart?
- Published values are nominal catalog diameters. Actual drill diameter can vary with brand, wear, runout, and material. For tight tolerances, measure the tool or verify on a test piece.
A number drill uses the # series from #80 (smallest, about 0.0135″) to #1 (largest, about 0.228″). Number drills fill gaps between fractional sizes and appear in standard drill size charts and tap drill tables.
Letter drills (A–Z) cover mid-range diameters when a fractional size is too small. Number drills extend finer and coarser. Both are listed in this drill bit size chart with drill diameter in mm and inches.
Multiply the decimal inch value by 25.4, or use the Diameter (mm) column in this drill size chart directly—no manual conversion needed during programming or inspection.
Use a tap drill chart or calculator, not the bolt clearance size. The correct pre-tap hole depends on thread series, pitch, and tap type. See our Tap Drill Size Calculator.
No. Fractional drills use common inch fractions (1/64, 1/32, etc.). Number and letter drills use separate naming systems. Shops reference all three in one drill size chart.
Published values are nominal catalog diameters. Actual drill diameter can vary with brand, wear, runout, and material. For tight tolerances, measure the tool or verify on a test piece.
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