Metric tap drill size calculator to calculate drill size for tapping metric thread according to ISO 2306 standard. Metric thread sizes from M1.6 to M56 for coarse and fine series threads are available.

Metric Tap Drill Size Calculator:

Metric Thread


Parameter Value
Designation --- ---
Nominal Diameter --- mm
Pitch ---
Screw Thread Series --- ---
Drill Diameter --- mm


Drill bit: A cutting tool used in drilling machines to drill a hole.

Tap: A mechanical tool used to make a standard thread through a hole. Different type of taps exist such as straight fluted taps, spiral pointed taps, spiral pointed only taps, spiral fluted taps, fast spiral fluted taps, thread forming taps, pulley taps, nut taps, and pipe taps.

Tap drill size: The required diameter of hole before the tapping operation of the hole.

Threads forming: A process to form threads by displacing the material to form the thread shape. No chips are produced during thread forming.

General Information

The diameter of a hole produced by a drill depends to some extent upon the degree of accuracy to which the drill point is ground, the material being drilled, the lubricant used, the alignment, feed and speed of the operation.

When tapping relatively soft material, there is a tendency for the material to be squeezed down towards the root and in such cases the minor diameter of the tapped hole may become smaller than the diameter of the drill used. The tendency is very much less with harder materials and in some cases is entirely absent.

The larger the drilled hole, within the relevant minor diameter tolerance, the more economical tapping becomes and the risk of tap breakage is reduced.

With the foregoing points in mind, the tables of ISO 2306 ( also results of the calculator) have been prepared as a guide to drilling prior to conventional tapping. However, it is realized that users may find it beneficial to choose their’ own drill diameters for certain applications. Even in these instances, stocked diameter drills should be used whenever possible.



  • ISO 68-1:1998(E) - ISO general purpose screw threads — Basic profile — Part 1: Metric screw threads
  • ISO 2306:1972, Drills for use prior to tapping screw threads