Drill Bit Size Chart for #36, #44, Number, Letter & Fractional Bits

Find the decimal and metric size for #36, #44, #11, #21, fractional, letter, and wire gauge drill bits before drilling, tapping, or choosing a pilot hole.

Quick Reference for Common Search Intents

Search IntentDecimal (in)Metric (mm)Practical Use Case
#36 Drill Bit0.1065 in2.705 mmStandard tap drill for 6-32 thread
#44 Drill Bit0.0860 in2.184 mmPrecision pilot for small fasteners
#11 Drill Bit0.1910 in4.851 mmCommon numbered size near 3/16 in
#21 Drill Bit0.1590 in4.039 mmPrecision numbered size near 5/32 in
1/8" Drill Bit0.1250 in3.175 mmCommon wood/metal DIY projects

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Number drill bit direct answers

For numbered drill bits, a smaller number usually means a larger bit. Use these direct answers when you need the decimal inch and metric size before tapping, drilling a pilot hole, or checking a worn bit with calipers.

Number drill bitDecimal inchesMetric mmCommon use note
#7 drill bit0.2010 in5.105 mmCommon tap drill size for 1/4-20 threads. Verify the thread chart before tapping.
#21 drill bit0.1590 in4.039 mmPrecision numbered size near 5/32 inch; useful when a fractional bit is not exact enough.
#29 drill bit0.1360 in3.454 mmCommon tap drill size for 8-32 threads. Use cutting fluid in metal to reduce tap breakage.
#36 drill bit0.1065 in2.705 mmStandard tap drill size for 6-32 threads.
#44 drill bit0.0860 in2.184 mmSmall numbered bit for precision pilot holes and light-duty fastener work.

Tap-drill recommendations vary by thread form, material, and required thread percentage. For metal tapping, confirm the thread standard and use cutting fluid. A slightly wrong bit can strip weak threads or break the tap inside the hole.

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Drill Bit Size Conversion Chart

Systems: Number, Fraction, Decimal, MM • Range 1/16 → 1/2 • A4

NumberFractionDecimal (in)Millimeters
1/16"0.06251.59
#520.06351.61
#510.06701.70
#500.07001.78
#490.07301.85
#480.07601.93
5/64"0.07811.98
#470.07851.99
0.07872.00
#460.08102.06
#450.08202.08
#440.08602.18
#430.08902.26
#420.09352.38
3/32"0.09382.38
#410.09602.44
#400.09802.49
0.09842.50
#390.09952.53
#380.10152.58
#370.10402.64
#360.10652.71
7/64"0.10942.78
#350.11002.79
#340.11102.82
#330.11302.87
#320.11602.95
0.11813.00
#310.12003.05
1/8"0.12503.17
#300.12853.26
#290.13603.45
0.13783.50
#280.14053.57
9/64"0.14063.57
#270.14403.66
#260.14703.73
#250.14953.80
#240.15203.86
#230.15403.91
5/32"0.15633.97
#220.15703.99
0.15754.00
#210.15904.04
#200.16104.09
#190.16604.22
#180.16954.30
11/64"0.17194.37
#170.17304.39
#160.17704.50
0.17724.50
#150.18004.57
#140.18204.62
#130.18504.70
3/16"0.18754.76
#120.18904.80
#110.19104.85
#100.19354.92
#90.19604.98
0.19695.00
#80.19905.05
#70.20105.11
13/64"0.20315.16
#60.20405.18
#50.20555.22
#40.20905.31
#30.21305.41
0.21655.50
7/32"0.21885.56
#20.22105.61
#10.22805.79
0.23405.94
15/64"0.23445.95
0.23626.00
0.23806.04
0.24206.15
0.24606.25
1/4"0.25006.35
0.25596.50
0.25706.53
0.26106.63
17/64"0.26566.75
0.26606.76
0.27206.91
0.27567.00
0.27707.04
0.28107.14
9/32"0.28137.14
0.29007.37
0.29507.49
0.29537.50
19/64"0.29697.54
0.30207.67
5/16"0.31257.94
0.31508.00
0.31608.03
0.32308.20
21/64"0.32818.33
0.33208.43
0.33468.50
0.33908.61
11/32"0.34388.73
0.34808.84
0.35439.00
0.35809.09
23/64"0.35949.13
0.36809.35
0.37409.50
3/8"0.37509.53
0.37709.58
0.38609.80
25/64"0.39069.92
0.393710.00
0.397010.08
0.404010.26
13/32"0.406310.32
0.413010.49
0.413410.50
27/64"0.421910.72
0.433111.00
7/16"0.437511.11
0.452811.50
29/64"0.453111.51
15/32"0.468811.91
0.472412.00
31/64"0.484412.30
0.492112.50
1/2"0.500012.70

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Understanding Drill Bit Sizing Systems

Drill bits in the US are categorized into three systems, each designed for specific manufacturing or construction precision:

  1. Fractional Sizes: From 1/64" to 1" (and up). These are the "general-purpose" bits used in most home shops for wood and basic metal projects.
  2. Wire Gauge (Number) Sizes: Designed for precision metalworking. Ranges from #1 (0.2280") down to #80 (0.0135"). These are essential for tapping machine threads accurately—using the wrong bit here often ruins the thread or breaks the tap.
  3. Letter Sizes: Designed to bridge the gaps between fractional sizes, ranging from A (0.2340") to Z (0.4130"). Machinists use these for creating tight clearance holes for bolts.

Selecting the Right Bit for Your Project

  • General Construction: When working with wood or standard light metal, fractional bits provide the most common and accessible sizing increments.
  • Machining & Tapping: Numbered wire gauge bits are non-negotiable for precision threading. Always verify the tap drill chart; for example, a #36 drill bit is the industry standard for 6-32 threads.
  • Precision Clearances: If you need a bolt to slide through a hole perfectly without "slop," letter-sized drill bits offer the precision tolerances fractional bits lack.

Wood Screw Pilot Hole Guide

Prevent split wood and stripped screws. Match your drill bit to the screw size and wood hardness.

Screw SizeSoftwood Pilot
(Pine, Cedar)		Hardwood Pilot
(Oak, Maple)		Clearance Hole
(Shank pass-through)
#41/16"5/64"1/8"
#61/16"5/64"9/64"
#85/64"3/32"11/64"
#103/32"7/64"3/16"
#127/64"1/8"7/32"
#149/64"11/64"1/4"

Which Drill Bit Type?

Expert guidance on selecting bit geometry and materials for professional results.

Twist Bit

Wood, Metal, Plastic

General purpose bits. Standard 118° is for soft materials; 135° split-point is for harder metals.

Brad Point

Wood Only

Precision center point prevents wandering. Ideal for clean holes in cabinetry.

Masonry Bit

Brick, Concrete

Carbide-tipped for masonry. Requires a hammer drill for best results.

Cobalt (M35/M42)

Hard Metals

Resistant to high heat. Best for stainless steel and professional machining.

Professional Drilling Tips

How to use this chart to improve your accuracy in the workshop.

Measure Diameter

If markings are worn, use a digital caliper to measure the drill shank. Cross-reference this with our Decimal column.

Prevent Bit Walking

In metal, use a Center Punch to create a dimple. In wood, use a Brad Point bit to ensure the hole starts exactly where intended.

Calculate Clearance

Always use a Clearance Hole for the screw shank so the threads only engage the second piece of material for a tight joint.

Common Uses for Specific Drill Bit Sizes

Selecting the right drill bit is essential for a clean and secure hole.

General Construction (Fractional)

Common sizes like 1/8", 1/4", and 3/8" are standard for drilling into wood, drywall, and plastic.

Threading and Tapping (Number/Wire Gauge)

Numbered drill bits are essential when creating threads in metal. Using the exact size prevents tap breakage and ensures strong threads. For example, using a #36 drill bit is critical before tapping a 6-32 thread. Planning to tap a hole? Reference our complete Bolt & Screw Sizes Chart to find the perfect drill bit for any thread.

Clearance Holes (Letter)

When a bolt needs to pass through a material without threading into it, letter-sized drill bits often provide the perfect clearance gap that fractional bits might miss. For general wood screws, ensure a tight fit by checking our Screw Size Reference. Need to convert measurements? Use our Fraction to Decimal Chart.

Tap Drill Selection Guide

Matching the correct drill bit to your tap ensures strong threads and prevents broken tools.

Thread SizeThreads / InchTap DrillDecimal (in)
6-32 UNC32#360.1065"
8-32 UNC32#290.1360"
10-24 UNC24#250.1495"
1/4"-20 UNC20#70.2010"
5/16"-18 UNC18Letter F0.2570"
M6 x 1.01.0mm5.0mm0.1969"

Related workshop charts for drilling and fasteners

Need to match the hole to a screw, bolt, or wrench size? Keep these workshop references together so you can move from drill size to fastener size without guessing.

Frequently Asked Questions

What size is a #44 drill bit?
A #44 drill bit is 0.0860 inches in diameter, which converts to 2.184 mm.
What size is a #11 drill bit?
A #11 drill bit is 0.1910 inches in diameter, which converts to 4.851 mm.
What size is a #21 drill bit?
A #21 drill bit is 0.1590 inches in diameter, which converts to 4.039 mm.
What is the closest substitute for a #44 drill bit?
The closest common substitute for a #44 drill bit is a 2.2 mm bit, which is slightly larger at about 0.0866 inches. Use the exact #44 size when thread fit or precision matters.
What is the actual diameter of a #1 wire gauge drill bit?
A #1 wire gauge drill bit has a decimal diameter of 0.2280 inches. In the number system, #1 is the largest, and #80 is the smallest (0.0135 inches).
What is the equivalent of a Letter F drill bit?
A Letter F drill bit has a decimal diameter of 0.2570 inches. It is most commonly used as the tap drill for a 5/16"-18 UNC thread.
What is the difference between 118° and 135° drill bits?
118-degree bits are general-purpose and ideal for wood and soft metals. 135-degree split-point bits are designed for harder metals (like stainless steel) because they 'bite' into the material and don't walk across the surface.
Which drill bit should I use for a 1/4"-20 tap?
The standard tap drill for a 1/4"-20 UNC thread is a #7 drill bit (0.2010 inches). This ensures approximately 75% thread engagement.
How do I convert millimeters to drill bit sizes?
Our chart lists the nearest MM equivalent for every number, letter, and fractional size. For example, a 6mm bit is slightly smaller than a 1/4" (6.35mm) bit.
What is a 'Wire Gauge' drill bit?
Wire gauge sizes are a numbered system (1-80) typically used for small-diameter precision drilling in machining and electronics.
What is a #36 drill bit used for?
A #36 wire gauge drill bit is the standard tap drill size for a 6-32 machine screw thread. Its diameter is 0.1065 inches (2.705 mm).
How do I choose between fractional and wire drill bits?
Choose fractional bits for general carpentry or clearance holes where loose tolerance is acceptable. Choose wire gauge bits for precision tasks like tapping metal, where exact diameter is required to ensure thread strength.
What is the smallest wire gauge drill bit?
The #80 drill bit is the smallest in the wire gauge system, measuring 0.0135 inches (0.343 mm).
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