The definition of wire mesh size:
5 mesh <------> there are 5 mesh holes in the length of 1 inch (25.4mm)
10 mesh <------>there are 10 mesh holes in the length of 1 inch (25.4mm)
20 mesh <------>there are 20 mesh holes in the length of 1 inch (25.4mm)
50 mesh <------>there are 50 mesh holes in the length of 1 inch (25.4mm)