drill size conversions

Drill Size Conversion Chart

Need to convert drill sizes quickly and accurately? Our free Drill Size Conversion tool helps you compare metric drill sizes, imperial drill sizes, fractional inches, decimal inches, number drills and letter drills.

Whether you are checking:

• mm drill sizes
• inch drill sizes
• fractional drill sizes
• number drill sizes
• letter drill sizes

This simple online tool makes drill size conversions fast and easy.

How to Convert Drill Sizes

Drill sizes can be shown in several different formats, including millimetres, decimal inches, fractions, number sizes and letter sizes.

Our Drill Size Conversion tool helps you compare these formats so you can quickly find the closest equivalent drill size.

Useful Conversion:

1 inch = 25.4mm

Drill Size Conversion Example

If you want to convert a 6mm drill size to inches:

6 ÷ 25.4 = 0.2362 inches

So, a 6mm drill bit is approximately 0.2362 inches.

What Are Metric Drill Sizes?

Metric drill sizes are measured in millimetres and are commonly used in the UK, Europe and many engineering applications.

What Are Imperial Drill Sizes?

Imperial drill sizes are measured in inches and may be shown as decimal inches or fractional inches.

What Are Number and Letter Drill Sizes?

Number and letter drill sizes are commonly used in machining, engineering and tapping applications. These sizes provide standard drill diameters that may not match simple metric or fractional inch sizes exactly.

Common Drill Size Conversions

• 1mm = 0.0394 inches
• 2mm = 0.0787 inches
• 3mm = 0.1181 inches
• 4mm = 0.1575 inches
• 5mm = 0.1969 inches
• 6mm = 0.2362 inches
• 8mm = 0.3150 inches
• 10mm = 0.3937 inches

Why Use Our Drill Size Conversion Tool?

• Compare metric and imperial drill sizes
• Find decimal inch equivalents
• Useful for DIY, engineering and machining
• Helps identify close matching drill sizes
• Simple and easy to use