A comprehensive drill bit size chart is one of those reference sheets you’ll use constantly. Whether you’re working in millimetres, fractional inches, number sizes, or letter sizes, this guide covers all of it. Bookmark it and you’ll never wonder “what size is a #12 bit” again.
Metric Drill Bit Sizes (0.5mm to 25mm)
Metric is straightforward—the bit size equals the hole diameter. A 5mm bit makes a 5mm hole. Here’s the full range:
| Size (mm) | Common Uses | Typical Material |
|---|---|---|
| 0.5 | Precision electronics, tiny holes | PCB drilling (specialist) |
| 1.0 | Very small pilot holes | Specialist, aircraft |
| 1.5 | Pilot holes for small screws | Electronics, wood |
| 2.0 | Pilot holes, cable holes | Metal, wood, plastic |
| 2.5 | Pilot holes for #4–#6 screws | Wood, metal |
| 3.0 | Pilot holes for #8 screws, small fixings | Wood, metal, masonry |
| 3.5 | M3 bolt holes, small fixings | Metal, masonry |
| 4.0 | M4 bolt holes, #8–#10 screws | Metal, wood, masonry |
| 4.5 | Small wall plugs (yellow) | Masonry |
| 5.0 | Yellow wall plugs, #4–#8 screws | Masonry, general fixings |
| 5.5 | M5 bolt clearance, general use | Metal, wood |
| 6.0 | Red wall plugs, #6–#10 screws | Masonry, general fixings |
| 6.5 | M6 bolt holes | Metal, machinery |
| 7.0 | Brown wall plugs, heavy fixings | Masonry |
| 8.0 | M8 bolt holes, blue wall plugs | Metal, masonry, heavy work |
| 9.0 | M9 bolt holes (rare) | Specialist |
| 10.0 | Blue wall plugs, large fixings | Masonry, heavy brackets |
| 11.0 | M11 bolts (rare) | Specialist |
| 12.0 | Grey wall plugs, M12 bolts | Masonry, heavy industrial |
| 13.0 | M13 bolts (rare) | Specialist |
| 14.0 | M14 bolts | Machinery, automotive |
| 15.0 | M15 bolts, large holes | Machinery |
| 16.0 | M16 bolts, large holes | Machinery, structural |
| 18.0 | M18 bolts, large holes | Heavy machinery |
| 20.0 | M20 bolts, pipe holes | Machinery, plumbing |
| 22.0 | M22 bolts, large pipes | Structural, machinery |
| 25.0 | Large holes, pipes | Plumbing, building |
Fractional Inch Drill Bit Sizes
Imperial (fractional inch) bits are common in the UK and US. This table shows the most common sizes used in everyday work, with metric equivalents:
| Fractional Size | Decimal (inches) | Metric (mm) | Common Uses |
|---|---|---|---|
| 1/16″ | 0.0625″ | 1.588 mm | Pilot holes, electronics |
| 3/32″ | 0.09375″ | 2.381 mm | Small pilot holes |
| 1/8″ | 0.125″ | 3.175 mm | Pilot holes for #8 screws |
| 5/32″ | 0.15625″ | 3.969 mm | General pilot holes |
| 3/16″ | 0.1875″ | 4.763 mm | Small wall plugs, general use |
| 7/32″ | 0.21875″ | 5.556 mm | Yellow wall plugs equivalent |
| 1/4″ | 0.25″ | 6.35 mm | Red wall plugs equivalent, general use |
| 9/32″ | 0.28125″ | 7.144 mm | Brown wall plugs equivalent |
| 5/16″ | 0.3125″ | 7.938 mm | General use, bolt holes |
| 11/32″ | 0.34375″ | 8.731 mm | Blue wall plugs equivalent |
| 3/8″ | 0.375″ | 9.525 mm | General use, bolt holes |
| 13/32″ | 0.40625″ | 10.319 mm | Large holes |
| 7/16″ | 0.4375″ | 11.112 mm | Large holes |
| 15/32″ | 0.46875″ | 11.906 mm | Grey wall plugs equivalent |
| 1/2″ | 0.5″ | 12.7 mm | Large holes, pipes |
| 9/16″ | 0.5625″ | 14.288 mm | Large holes |
| 5/8″ | 0.625″ | 15.875 mm | Large holes, pipes |
| 3/4″ | 0.75″ | 19.05 mm | Large holes, plumbing |
| 7/8″ | 0.875″ | 22.225 mm | Very large holes |
| 1″ | 1.0″ | 25.4 mm | Very large holes, pipes |
Numbered Drill Bit Sizes (#1 to #60)
Numbered bits (also called wire gauge sizes) are less common in the UK than metric or fractional, but they’re still used, especially in precision work and on older equipment. Here are the most common numbered sizes:
| Number Size | Decimal (inches) | Metric (mm) | Notes |
|---|---|---|---|
| #1 | 0.2280″ | 5.79 mm | Large numbered bit |
| #10 | 0.1935″ | 4.91 mm | Common for screws |
| #20 | 0.1610″ | 4.09 mm | Precision drilling |
| #30 | 0.1285″ | 3.26 mm | Small holes |
| #40 | 0.0980″ | 2.49 mm | Precision electronics |
| #50 | 0.0700″ | 1.78 mm | Very small holes |
| #60 | 0.0400″ | 1.02 mm | Tiny precision holes |
Note: Numbered bits run in reverse—higher number = smaller bit. A #1 is the largest numbered bit, #60 is tiny. This is counterintuitive compared to fractional sizes, which increase in size as the numerator increases.
Letter Drill Bit Sizes (A to Z)
Letter sizes (A–Z) are specialty bits, mostly used in precision engineering and tool-and-die work. They fall between numbered and fractional sizes. Here are the most common:
| Letter Size | Decimal (inches) | Metric (mm) | Close Metric Equivalent |
|---|---|---|---|
| A | 0.2340″ | 5.944 mm | ~6 mm |
| B | 0.2380″ | 6.045 mm | ~6 mm |
| C | 0.2420″ | 6.147 mm | ~6 mm |
| D | 0.2460″ | 6.248 mm | ~6 mm |
| E | 0.2500″ | 6.35 mm | ~6–6.5 mm |
| F | 0.2570″ | 6.527 mm | ~6.5 mm |
| G | 0.2610″ | 6.629 mm | ~6.5 mm |
| H | 0.2660″ | 6.756 mm | ~6.5–7 mm |
| I | 0.2720″ | 6.909 mm | ~7 mm |
| J | 0.2770″ | 7.036 mm | ~7 mm |
| K | 0.2810″ | 7.137 mm | ~7 mm |
| L | 0.2900″ | 7.366 mm | ~7–7.5 mm |
| M | 0.2950″ | 7.493 mm | ~7.5 mm |
| N | 0.3020″ | 7.671 mm | ~7.5–8 mm |
| O | 0.3160″ | 8.026 mm | ~8 mm |
| P | 0.3230″ | 8.204 mm | ~8 mm |
| Q | 0.3320″ | 8.433 mm | ~8–8.5 mm |
| R | 0.3390″ | 8.611 mm | ~8.5 mm |
| S | 0.3480″ | 8.839 mm | ~8.5–9 mm |
| T | 0.3580″ | 9.093 mm | ~9 mm |
| U | 0.3680″ | 9.347 mm | ~9–9.5 mm |
| V | 0.3770″ | 9.576 mm | ~9.5 mm |
| W | 0.3860″ | 9.804 mm | ~10 mm |
| X | 0.3970″ | 10.084 mm | ~10 mm |
| Y | 0.4040″ | 10.262 mm | ~10 mm |
| Z | 0.4130″ | 10.490 mm | ~10.5 mm |
Metric to Imperial Quick Conversion
For everyday reference, here are the most common metric sizes and their nearest imperial equivalents:
| Metric (mm) | Nearest Imperial | Decimal Inches |
|---|---|---|
| 2.0 | 5/64″ | 0.078″ |
| 2.5 | 3/32″ | 0.094″ |
| 3.0 | 1/8″ | 0.125″ |
| 4.0 | 5/32″ | 0.156″ |
| 5.0 | 3/16″ | 0.188″ |
| 6.0 | 1/4″ | 0.250″ |
| 8.0 | 5/16″ | 0.313″ |
| 10.0 | 3/8″ | 0.375″ |
| 12.0 | 1/2″ | 0.500″ |
| 16.0 | 5/8″ | 0.625″ |
| 20.0 | 3/4″ | 0.750″ |
| 25.0 | 1″ | 1.000″ |
Tap Drill Sizes (Clearance and Tapping)
When drilling holes for bolts or threaded inserts, you need different sizes for different purposes:
Clearance hole: The bolt passes through freely without threading (bolt screws into something on the other side).
Tapping hole: You’ll cut a thread inside the hole (internal threading for a bolt to screw into).
| Bolt Size | Clearance Hole (mm) | Tapping Hole (mm) | Best Tap Drill Size |
|---|---|---|---|
| M3 | 3.5 | 2.5 | 2.5 mm |
| M4 | 4.5 | 3.0 | 3.0 mm |
| M5 | 5.5 | 4.2 | 4.0 or 4.2 mm |
| M6 | 6.5 | 5.0 | 5.0 mm |
| M8 | 9.0 | 6.8 | 6.5 or 6.8 mm |
| M10 | 11.0 | 8.5 | 8.5 mm |
| M12 | 13.5 | 10.2 | 10.0 or 10.2 mm |
Rule of thumb: For metric tapping holes, subtract 1.5 from the bolt size. M5 → tap at 3.5, M8 → tap at 6.5, M10 → tap at 8.5, etc. This leaves enough material to cut a strong thread.
Most Common Sizes for Everyday Work
If you only buy one set of bits, make it these—they cover 90% of DIY and trade work:
Metric basics: 2.0, 2.5, 3.0, 4.0, 5.0, 6.0, 8.0, 10.0 mm
Wall plugs: 5.0 (yellow), 6.0 (red), 10.0 (blue) mm
Bolt holes: 3.5 (M3), 4.5 (M4), 5.5 (M5), 6.5 (M6), 9.0 (M8) mm
Fractional (if you work in inches): 1/16″, 1/8″, 5/32″, 3/16″, 1/4″, 5/16″, 3/8″, 1/2″
These 16 sizes handle the vast majority of drilling jobs. Specialist bits (large hole saws, numbered, letter sizes) you can add as needed.
Tips for Using This Chart
- Metric bits are easiest: 5mm bit = 5mm hole. Simple. Metric is standard on modern tools.
- For conversions: Divide mm by 25.4 to get inches, or multiply inches by 25.4 to get mm. Use the quick reference table above for common sizes.
- Numbered and letter sizes are specialist: You’ll rarely need them unless you’re doing precision engineering or old-school machinist work.
- Clearance vs tapping: Always use a larger clearance hole (bolt passes through) than a tapping hole (you cut a thread). See the tap drill table above.
- Wall plugs: Drill bit size must match plug size exactly. 5mm plug = 5mm bit. See the earlier drill bit guides for full details.
Amazon: Metric Drill Bit Sets on Amazon UK
Amazon: Drill Bit Index Sets on Amazon UK
See also: What Drill Bit for Wood
See also: What Drill Bit for Masonry
See also: Wall Plug Drill Bit Size Guide
Watch: Video Guide
Frequently Asked Questions
What do the numbers on drill bits mean?
For metric bits, the number is the hole diameter in millimetres. A 5mm bit makes a 5mm hole. For numbered bits (old wire gauge system), the number is confusing—higher numbers mean smaller bits (opposite of fractional sizes). Letter sizes fall between numbered and fractional. Unless you’re doing precision engineering, stick with metric.
How do I convert drill bit sizes between mm and inches?
Divide mm by 25.4 to get inches: 6mm ÷ 25.4 = 0.236″. Multiply inches by 25.4 to get mm: 1/4″ × 25.4 = 6.35mm. The quick reference table above shows the most common conversions, so you don’t have to calculate every time.
What’s the difference between a clearance hole and a tapping hole?
A clearance hole is larger—the bolt passes through freely. A tapping hole is smaller—you cut threads inside it for a bolt to screw into. For M5 bolts: clearance hole is 5.5mm, tapping hole is 4.2mm. Always use the tap drill size from the table to ensure enough material for a strong thread.
What are numbered and letter drill bits used for?
Numbered (#1 to #60) and letter (A to Z) bits are specialist sizes used in precision engineering, toolmaking, and old equipment. They fall between fractional and metric sizes. Most DIYers and tradespeople never need them. Stick with metric or fractional sizes.
What’s the smallest and largest drill bit?
Speciality bits go down to 0.5mm (tiny precision holes) and up to 50mm or larger (hole saws). For practical DIY work, 2mm to 13mm covers most jobs. Larger holes (16–50mm) use spade bits or hole saws instead of twist bits.
How do I choose between metric and imperial bits?
Use metric if working on metric machines or with metric specifications (bolts, wall plugs). Use fractional inches if working on older equipment or with imperial specifications. In the UK, metric is standard on modern tools. If you’re not sure, buy metric.
