Yar68 is correct, but in general:
I think GMB flags are a good standard IMHO.
Using an infantry regiment flag:
When folded over the flag should approximately be around 4.2 cm long x 3.8cm high. Flag poles will very, but when deciding the length I'd consider that you don't want the flag too high up on the pole or starting at the hand so from the top of the hand I'd start anywhere between .5cm and 1cm. up works pretty good in most cases.
I hope I made sense and was somewhat helpful.
Christopher