Tap Drill Size Calculator

Introduction: When it comes to tapping threads for screws and bolts, using the correct tap drill size is essential for achieving a secure and effective connection. The Tap Drill Size Calculator provides a convenient way to determine the optimal drill size based on thread diameter and pitch.

Formula: The calculation is based on the formula: Tap Drill Size = Thread Diameter – 1 / Thread Pitch. This formula takes into account the thread diameter and pitch to calculate the suitable drill size for tapping.

How to Use:

  1. Enter the thread diameter (in inches) in the designated field.
  2. Input the thread pitch (threads per inch) based on your requirements.
  3. Click the “Calculate” button to obtain the recommended tap drill size.

Example: For a thread diameter of 0.25 inches and a thread pitch of 20 threads per inch, enter these values, click “Calculate,” and the result will indicate the appropriate tap drill size.


  1. Q: Why is the tap drill size important for threading? A: Using the correct tap drill size ensures a proper fit for threads, contributing to the strength and reliability of the connection.
  2. Q: Can the calculator be used for metric threads? A: No, this calculator is designed for imperial threads. For metric threads, a different calculation is required.

Conclusion: The Tap Drill Size Calculator is a valuable tool for anyone involved in metalworking or woodworking, providing a quick and accurate way to determine the optimal drill size for tapping threads. By using this calculator, you can enhance the precision and reliability of threaded connections in your projects.

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