The William Mitchell Round Hand Nibs are amongst the most popular edged nibs used by calligraphers. But the nib sizes are not so popular. Unlike the Brause Bandzug nibs and others, they do not have any measurements to indicate their size in millimetres.
Instead they are assigned a number. Size ‘0’ is the largest and size ‘6’ the smallest. Even this is confusing as size 6 sounds like it should be larger than the size 0. It’s a shame the numbers on the William Mitchell (and Leonardt Round Hand nibs) do not relate to their actual width.Below is a chart giving the size of each nib in millimetres. These sizes are also the same for the Leonardt Round Hand Nibs
* Inch sizes have been rounded and shown as fractions of an Inch rather than a decimal value. This rounding has given the anomaly of some nibs being the same size.Accurately ruling-up some of the smaller nibs sizes can be very tricky. For example, 5 nib widths of a Number 6 nib is 2.5mm or 3/32”. This problem resulted in the development of the X-Height Measuring Discs