40 count and higher

What about the dimensions of the embroidery linen? In the metric system, the fineness of the linen is indicated by the number of threads per centimeter. The higher this number, the finer the linen and the smaller the crosses become.
In countries where inches are calculated, the number of threads per inch (1 inch = 2.54 cm) is shown, this is called the fabric "count".

15.7 threads per cm = 7.8 crosses per cm (i.e. 40 count = 20 crosses per inch)
18 threads per cm = 9 crosses per cm (i.e. 45 / 46 count = 23 crosses per inch
21.6 threads per cm = 10.8 crosses per cm (ie 55 count = 27 crosses per inch)

This is very fine linen! To be able to see this properly, I recommend working in good (day) light and use, for example, loupe glasses.