When it comes to drilling holes—whether you’re working with wood, metal, plastic, or masonry—choosing the right drill bit size is crucial. A drill bit that’s too large or too small can ruin your project, damage materials, or even cause safety hazards. That’s why a drill bit size chart is one of the most valuable references for DIY enthusiasts, mechanics, engineers, and professional builders alike.
In this complete guide, we’ll cover everything you need to know about drill bit sizes, how to read a drill bit size chart, types of drill bits, and practical tips for selecting the correct one for your project.
Why Drill Bit Size Matters
Before diving into the chart itself, let’s understand why size matters so much:
Accuracy in Hole Making: If your drill bit doesn’t match the required hole size, your screw, bolt, or fastener won’t fit properly. This can lead to weak joints or even structural failure.
Preventing Material Damage: Using the wrong size can cause splitting in wood, cracking in masonry, or deformation in metal.
Tool Longevity: Matching the correct bit size with the right material reduces wear and tear, extending the life of both your drill and the bit.
Professional Results: Precision matters in carpentry, construction, and machining. The right size ensures your work looks clean, accurate, and reliable.
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Types of Drill Bit Size Measurements
Drill bit sizes are expressed in several different systems depending on the country, industry, or tool standard. These include:
Fractional Inch Sizes
Common in the United States.
Range: from 1/64″ (very small) up to several inches.
Number Sizes (Wire Gauge System)
Labeled from #80 (smallest) to #1 (largest).
Often used for very fine work in electronics, jewelry, and precision machining.
Letter Sizes
Range from A (smallest) to Z (largest).
Used in machinist applications where fractional sizes don’t offer enough accuracy.
Metric Sizes
Expressed in millimeters (mm).
Common worldwide, especially in engineering and automotive fields.
Range: 0.2 mm (tiny) up to 25 mm or more.
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Standard Drill Bit Size Chart
Here’s a simplified drill bit size chart showing the relationship between different measurement systems:
| Fractional (inches) | Decimal (inches) | Metric (mm) | Number Size | Letter Size |
|---|---|---|---|---|
| 1/16″ | 0.0625 | 1.59 mm | #52 | – |
| 5/64″ | 0.0781 | 1.98 mm | #47 | – |
| 3/32″ | 0.0938 | 2.38 mm | #42 | – |
| 7/64″ | 0.1094 | 2.78 mm | #36 | – |
| 1/8″ | 0.1250 | 3.18 mm | #30 | – |
| 9/64″ | 0.1406 | 3.57 mm | #28 | – |
| 5/32″ | 0.1563 | 3.97 mm | #25 | – |
| 11/64″ | 0.1719 | 4.37 mm | #21 | – |
| 3/16″ | 0.1875 | 4.76 mm | #14 | – |
| 13/64″ | 0.2031 | 5.16 mm | #11 | – |
| 7/32″ | 0.2188 | 5.56 mm | #3 | – |
| 15/64″ | 0.2344 | 5.95 mm | – | A |
| 1/4″ | 0.2500 | 6.35 mm | – | B |
| 17/64″ | 0.2656 | 6.75 mm | – | F |
| 5/16″ | 0.3125 | 7.94 mm | – | I |
| 3/8″ | 0.3750 | 9.53 mm | – | U |
| 1/2″ | 0.5000 | 12.70 mm | – | Z |
This is only a partial chart. Full charts often include every fractional step, all letter sizes, and wire gauge numbers.
Common Drill Bit Sizes for Everyday Use
1/16″ (1.6 mm): Small pilot holes, delicate tasks.
1/8″ (3.2 mm): General-purpose for screws in wood or drywall.
3/16″ (4.8 mm): Useful for medium screws and bolts.
1/4″ (6.4 mm): Common for wall anchors and lag screws.
3/8″ (9.5 mm): Larger holes, bolts, or dowels.
1/2″ (12.7 mm): Heavy-duty drilling in wood or metal.
Drill Bit Size for Tapping (Screw Threads)
If you’re drilling a hole to tap threads (for bolts or screws), you need to know the tap drill size. Here’s a quick reference:
For 1/4″-20 UNC bolt → Drill size #7 (0.201″)
For 3/8″-16 UNC bolt → Drill size 5/16″
For M6 x 1.0 metric screw → Drill size 5.0 mm
For M10 x 1.5 metric screw → Drill size 8.5 mm
Always check a tapping drill chart for precision.
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How to Read and Use a Drill Bit Size Chart
Identify Your Requirement: Are you drilling for a screw, a dowel, a wall anchor, or a clearance hole? Each has different requirements.
Check the Fastener Size: Match the screw or bolt size to the chart to find the recommended drill bit.
Convert Units If Needed: If your project uses metric screws but your drill bits are fractional, use the chart for conversions.
Select Closest Match: If you don’t have the exact size, choose the closest available bit, but avoid going larger than required.
Types of Drill Bits and Their Uses
Different jobs require different types of drill bits. Some common ones include:
Twist Drill Bits
Standard type, works for wood, metal, and plastic.
Available in most fractional, metric, and number sizes.
Brad-Point Bits
Designed for woodworking.
Sharp center point prevents wandering.
Masonry Bits
For brick, stone, and concrete.
Often used with hammer drills.
Spade Bits
Wide and flat, designed for drilling large holes in wood.
Forstner Bits
Make clean, flat-bottomed holes in wood.
Step Drill Bits
Cone-shaped, used for sheet metal.
Can drill multiple hole sizes with one bit.
Auger Bits
For deep wood boring, often used with hand drills.
Tips for Choosing the Right Drill Bit
Match material to bit: Use masonry bits for concrete, wood bits for timber, and high-speed steel or cobalt bits for metal.
Use pilot holes: Start with a small bit, then step up to the larger required size.
Keep bits sharp: A dull bit can damage materials and increase drill wear.
Check shank size: Ensure your drill chuck can hold the bit.
Use lubrication for metal drilling: Cutting oil reduces heat and extends bit life.
Storing and Organizing Drill Bits
A size chart is useful only if you can quickly match it with the actual drill bit in your kit. To stay organized:
Store drill bits in labeled cases.
Keep a laminated drill bit size chart in your workshop.
Arrange bits in ascending order for quick access.
Replace missing or worn bits promptly.
Final Thoughts
A drill bit size chart is more than just a list of numbers—it’s a roadmap to precision and efficiency in drilling. Whether you’re assembling furniture, repairing a car, or fabricating machinery, choosing the correct bit size ensures your project turns out strong, accurate, and professional.
By understanding different measurement systems—fractional, number, letter, and metric—you can confidently convert and select the right size for any job. Pair that knowledge with the correct type of drill bit, and you’ll be equipped to handle almost any drilling task with confidence.
Keep this guide and chart handy in your workshop. It will save you time, prevent mistakes, and help you achieve the best results in every project.
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