Drill Bit Size Chart: Metric, Fractional & Number Sizes Converted
Use the calculator to convert between systems instantly, or scroll to the full number, letter, fractional, and metric tables below.
Drill Size Converter (mm → fractional)
What Is a Drill Bit Size Chart?
A drill bit size chart cross-references metric (mm), fractional inch, number (#1 through #80), and letter (A through Z) drill bit sizes. The four systems coexist because machinists, gunsmiths, electricians, and woodworkers each standardized their own size steps at different points in history, and all four remain in daily use. A complete reference lets a user pick the closest available bit to the diameter a job actually needs, regardless of which system their drill index uses.
Number and letter sizes fill in gaps that fractional inches leave too coarse for tapping, reaming, and jig work: a fractional set jumps from 7/32 inch straight to 1/4 inch, a gap of 0.031 inch, while the number and letter systems break that same range into six or seven finer steps.
Number Drill Sizes (#80 to #1)
| Number | Inches | mm |
|---|---|---|
| #80 | 0.0135" | 0.343mm |
| #76 | 0.0200" | 0.508mm |
| #70 | 0.0280" | 0.711mm |
| #65 | 0.0350" | 0.889mm |
| #60 | 0.0400" | 1.016mm |
| #55 | 0.0520" | 1.321mm |
| #50 | 0.0700" | 1.778mm |
| #45 | 0.0820" | 2.083mm |
| #40 | 0.0980" | 2.489mm |
| #35 | 0.1100" | 2.794mm |
| #30 | 0.1285" | 3.264mm |
| #25 | 0.1495" | 3.797mm |
| #20 | 0.1610" | 4.089mm |
| #15 | 0.1800" | 4.572mm |
| #10 | 0.1935" | 4.915mm |
| #5 | 0.2055" | 5.220mm |
| #1 | 0.2280" | 5.791mm |
Letter Drill Sizes (A to Z)
| Letter | Inches | mm |
|---|---|---|
| A | 0.2340" | 5.944mm |
| B | 0.2380" | 6.045mm |
| C | 0.2420" | 6.147mm |
| D | 0.2460" | 6.248mm |
| E | 0.2500" | 6.350mm |
| F | 0.2570" | 6.528mm |
| G | 0.2610" | 6.629mm |
| H | 0.2660" | 6.756mm |
| I | 0.2720" | 6.909mm |
| J | 0.2770" | 7.036mm |
| K | 0.2810" | 7.137mm |
| L | 0.2900" | 7.366mm |
| M | 0.2950" | 7.493mm |
| N | 0.3020" | 7.671mm |
| O | 0.3160" | 8.026mm |
| P | 0.3230" | 8.204mm |
| Q | 0.3320" | 8.433mm |
| R | 0.3390" | 8.611mm |
| S | 0.3480" | 8.839mm |
| T | 0.3580" | 9.093mm |
| U | 0.3680" | 9.347mm |
| V | 0.3770" | 9.576mm |
| W | 0.3860" | 9.804mm |
| X | 0.3970" | 10.084mm |
| Y | 0.4040" | 10.262mm |
| Z | 0.4130" | 10.490mm |
Fractional Drill Sizes (1/64" to 1")
| Fraction | Decimal Inches | mm |
|---|---|---|
| 1/64" | 0.0156" | 0.397mm |
| 1/32" | 0.0313" | 0.794mm |
| 3/64" | 0.0469" | 1.191mm |
| 1/16" | 0.0625" | 1.587mm |
| 5/64" | 0.0781" | 1.984mm |
| 3/32" | 0.0938" | 2.381mm |
| 7/64" | 0.1094" | 2.778mm |
| 1/8" | 0.1250" | 3.175mm |
| 9/64" | 0.1406" | 3.572mm |
| 5/32" | 0.1563" | 3.969mm |
| 11/64" | 0.1719" | 4.366mm |
| 3/16" | 0.1875" | 4.762mm |
| 13/64" | 0.2031" | 5.159mm |
| 7/32" | 0.2188" | 5.556mm |
| 15/64" | 0.2344" | 5.953mm |
| 1/4" | 0.2500" | 6.350mm |
| 17/64" | 0.2656" | 6.747mm |
| 9/32" | 0.2813" | 7.144mm |
| 19/64" | 0.2969" | 7.541mm |
| 5/16" | 0.3125" | 7.938mm |
| 21/64" | 0.3281" | 8.334mm |
| 11/32" | 0.3438" | 8.731mm |
| 23/64" | 0.3594" | 9.128mm |
| 3/8" | 0.3750" | 9.525mm |
| 25/64" | 0.3906" | 9.922mm |
| 13/32" | 0.4063" | 10.319mm |
| 27/64" | 0.4219" | 10.716mm |
| 7/16" | 0.4375" | 11.112mm |
| 29/64" | 0.4531" | 11.509mm |
| 15/32" | 0.4688" | 11.906mm |
| 31/64" | 0.4844" | 12.303mm |
| 1/2" | 0.5000" | 12.700mm |
| 33/64" | 0.5156" | 13.097mm |
| 17/32" | 0.5313" | 13.494mm |
| 35/64" | 0.5469" | 13.891mm |
| 9/16" | 0.5625" | 14.287mm |
| 37/64" | 0.5781" | 14.684mm |
| 19/32" | 0.5938" | 15.081mm |
| 39/64" | 0.6094" | 15.478mm |
| 5/8" | 0.6250" | 15.875mm |
| 41/64" | 0.6406" | 16.272mm |
| 21/32" | 0.6563" | 16.669mm |
| 43/64" | 0.6719" | 17.066mm |
| 11/16" | 0.6875" | 17.462mm |
| 45/64" | 0.7031" | 17.859mm |
| 23/32" | 0.7188" | 18.256mm |
| 47/64" | 0.7344" | 18.653mm |
| 3/4" | 0.7500" | 19.050mm |
| 49/64" | 0.7656" | 19.447mm |
| 25/32" | 0.7813" | 19.844mm |
| 51/64" | 0.7969" | 20.241mm |
| 13/16" | 0.8125" | 20.637mm |
| 53/64" | 0.8281" | 21.034mm |
| 27/32" | 0.8438" | 21.431mm |
| 55/64" | 0.8594" | 21.828mm |
| 7/8" | 0.8750" | 22.225mm |
| 57/64" | 0.8906" | 22.622mm |
| 29/32" | 0.9063" | 23.019mm |
| 59/64" | 0.9219" | 23.416mm |
| 15/16" | 0.9375" | 23.813mm |
| 61/64" | 0.9531" | 24.209mm |
| 31/32" | 0.9688" | 24.606mm |
| 63/64" | 0.9844" | 25.003mm |
| 1" | 1.0000" | 25.400mm |
Metric Drill Sizes (0.5mm to 25mm)
| mm | Inches | Nearest Fraction |
|---|---|---|
| 0.5mm | 0.0197" | 1/64" |
| 1mm | 0.0394" | 3/64" |
| 1.5mm | 0.0591" | 1/16" |
| 2mm | 0.0787" | 5/64" |
| 2.5mm | 0.0984" | 3/32" |
| 3mm | 0.1181" | 1/8" |
| 3.5mm | 0.1378" | 9/64" |
| 4mm | 0.1575" | 5/32" |
| 4.5mm | 0.1772" | 11/64" |
| 5mm | 0.1969" | 13/64" |
| 5.5mm | 0.2165" | 7/32" |
| 6mm | 0.2362" | 15/64" |
| 6.5mm | 0.2559" | 1/4" |
| 7mm | 0.2756" | 9/32" |
| 7.5mm | 0.2953" | 19/64" |
| 8mm | 0.3150" | 5/16" |
| 8.5mm | 0.3346" | 21/64" |
| 9mm | 0.3543" | 23/64" |
| 9.5mm | 0.3740" | 3/8" |
| 10mm | 0.3937" | 25/64" |
| 10.5mm | 0.4134" | 13/32" |
| 11mm | 0.4331" | 7/16" |
| 11.5mm | 0.4528" | 29/64" |
| 12mm | 0.4724" | 15/32" |
| 12.5mm | 0.4921" | 31/64" |
| 13mm | 0.5118" | 33/64" |
| 13.5mm | 0.5315" | 17/32" |
| 14mm | 0.5512" | 35/64" |
| 14.5mm | 0.5709" | 37/64" |
| 15mm | 0.5906" | 19/32" |
| 15.5mm | 0.6102" | 39/64" |
| 16mm | 0.6299" | 5/8" |
| 16.5mm | 0.6496" | 21/32" |
| 17mm | 0.6693" | 43/64" |
| 17.5mm | 0.6890" | 11/16" |
| 18mm | 0.7087" | 45/64" |
| 18.5mm | 0.7283" | 47/64" |
| 19mm | 0.7480" | 3/4" |
| 19.5mm | 0.7677" | 49/64" |
| 20mm | 0.7874" | 25/32" |
| 20.5mm | 0.8071" | 13/16" |
| 21mm | 0.8268" | 53/64" |
| 21.5mm | 0.8465" | 27/32" |
| 22mm | 0.8661" | 55/64" |
| 22.5mm | 0.8858" | 57/64" |
| 23mm | 0.9055" | 29/32" |
| 23.5mm | 0.9252" | 59/64" |
| 24mm | 0.9449" | 15/16" |
| 24.5mm | 0.9646" | 31/32" |
| 25mm | 0.9843" | 63/64" |
How to Choose the Right Drill Size
Three jobs need three different sizing rules. For a clearance hole, one that a bolt passes through freely, pick the drill size just above the bolt's shaft diameter. For a press fit, where the part should grip the material, pick one or two sizes under the finished dimension. For tapping a thread, use the dedicated tap drill chart, since the correct size leaves enough material for the tap to cut full-depth threads, usually at 75% thread engagement.
Drill Bit Types and Coatings
A twist bit is the general-purpose default for metal, plastic, and wood. A brad point bit adds a center spur that prevents wandering in wood. A masonry bit uses a carbide tip to survive concrete and brick, and needs a hammer drill for anything beyond a shallow hole. Black oxide and titanium nitride coatings reduce friction and heat buildup in steel, extending bit life. Cobalt bits hold an edge at higher temperatures and cut stainless steel and hardened metal that a standard high-speed steel bit would dull against quickly.
Drill Bit Size for Tapping Threads
The tap drill runs slightly smaller than the bolt's major diameter, leaving enough metal for the tap to cut full threads without tearing them. For an M6 × 1.0 thread, the tap drill is 5.0mm. For a 1/4 inch-20 thread, the tap drill is a #7 bit (0.201 inch), or 5.1mm in metric. The complete table covering every common metric and SAE thread size is on the tap drill chart page.
Drill Bit Size FAQ
What drill bit size is closest to 1/4 inch?
The 1/4 inch fractional bit itself (0.250 inch) is standard, but the letter D bit (0.246 inch) and letter E bit (0.250 inch) are the closest number/letter equivalents when a fractional set is not on hand.
What is the difference between a number drill and a letter drill?
Number drills (#80 through #1) cover the smallest sizes, from 0.0135 to 0.228 inch. Letter drills (A through Z) pick up where numbers leave off, covering 0.234 to 0.413 inch. Together they fill the gaps between fractional sizes for precision work like tapping and reaming.
Do I need a bigger or smaller drill bit for a bolt to pass through freely?
Bigger. A clearance hole uses a bit slightly larger than the bolt's shaft diameter, so the bolt passes through without engaging threads in the material it's passing through.
What size drill bit do I need to tap an M6 thread?
A 5.0mm drill bit is the standard tap drill for an M6 × 1.0 thread, giving about 75% thread engagement. See the tap drill chart for every metric and SAE thread size.
Can I use a metric drill bit for a fractional-inch hole?
Yes, if the metric size is close enough for the tolerance the job needs. A 6mm bit (0.2362 inch) is 0.012 inch smaller than 1/4 inch (0.250 inch), which is fine for a clearance hole but too tight for a precision fractional fit.
Why do drill bit sizes use four different systems?
Number and letter sizes exist because early machinists needed finer size steps than fractions alone provided, especially for the small increments used in tapping and jig work. Metric sizes exist because most of the world outside the US builds to metric standards. All four systems stayed in use because too much existing tooling and documentation depends on each.