TAP-DRILL SIZE CALCULATOR

To minimize tapping problems and lengthen tool life, use the largest drill possible to produce a minor diameter that will result in the lowest percentage of full thread consistent with adequate strength. A minor diameter that provides a 55% to 65% thread is sufficient for most requirements, but in some cases a higher percentage of thread may be necessary to conform with the minor diameter limits of the thread class specified.
Drills generally cut holes larger than their diameters. In the form bellow, the probable percentages of full thread were determined by the average amount oversize the various drills are expected to cut. Reaming becomes necessary when close control of the hole size is required.

• Calculate Hole Size for Inch Cutting Taps
• Calculate Hole Size for Metric Cutting Taps
• Calculate Hole Size for Inch Forming Taps
• Calculate Hole Size for Metric Forming Taps