In practice, you will seldom see number sizes past #80. The ASME B94.11M twist drill standard establishes number drill bit sizes from size 1 to 97. Number Drill Bit Sizes & Letter Drill Bit Sizes Decimal Equivalence ChartĪ good drill size chart can also be used as a handy decimal equivalence chart as well as to convert decimal sizes to metric. After that they run in 1/32″ increments up to 2 1/4″, then in 1/16″ increments to 3″, 1/8″ increments to 3 1/4 inches, then there’s a 3 1/2″ size. Fractional-Inch Drill Bit Sizesįractional-inch sizes are in common use in the US and generally run from 1/64 inch up to 1 3/4 inch in 1/64″ increments. There are also Reynard Series of preferred metric drill sizes. So for N = 2, it’s 2 – 0.1, etc.įrom 1 through 2.95mm, using N from 10 through 29, we get:įor 3 through 13.9mm, with N from 30 to 139:įor 14 through 25mm, and N from 14 through 25: Standard metric lengths (from standards like BS 32*) define metric drill bit sizes using this system:įor 0.2 to 0.98mm, sizes use N from 2 through 9:
Number Drill Bit Sizes & Letter Drill Bit Sizes.
