Tap & Drill Size Calculator

How to Use the Tap & Drill Size Calculator

Just choose your thread type (inch or metric), select the tap size or pitch, and set your desired thread engagement. 

Why Correct Drill Size Matters

Using the right drill bit before tapping ensures proper thread depth, reduces tool wear, and helps achieve the ideal amount of thread engagement—usually around 70–75% for most applications. Undersized holes can cause broken taps, while oversized holes lead to weak or incomplete threads. This calculator eliminates the guesswork by giving you the exact drill size needed for your specific tap.

Fast, Accurate, and Free

This tool is available online 24/7 and is completely free to use. It’s built to save you time on the shop floor and help ensure every tapped hole is cut cleanly and consistently.

Frequently Asked Questions

What drill size do I need for a tapped hole? The correct drill size depends on the tap size, thread pitch, and desired thread engagement. Our drill/tap calculator automatically determines the recommended drill bit size to ensure proper thread formation and strength.

What happens if my drill size is too small? If the drill size is too small, the tap must remove more material, which can lead to: Broken taps, excessive cutting force, and/or poor thread quality. Using the recommended drill size helps reduce tap breakage and produces cleaner, more consistent threads.

What happens if my drill size is too large? If the drill size is too large, the threads may be shallow, weak, and more likely to strip under load. Proper drill sizing ensures sufficient thread engagement without overstressing the tap.

Is 75% thread engagement enough? Yes! 75% thread engagement is ideal for most applications. It provides excellent holding strength while reducing tapping torque and tool wear. Higher engagement offers minimal strength gains but greatly increases the risk of tap breakage.

Does material type affect drill size? Material doesn’t change the drill size, but it can affect recommended thread engagement. Harder materials, such as stainless steel, may benefit from slightly lower engagement, while softer materials, such as aluminum, can tolerate higher engagement.

Should I always follow the tap manufacturer’s recommendation? Yes! While this calculator provides industry-standard recommendations, always verify against your tap manufacturer’s specifications, especially for specialty taps or critical applications.