All samples taken during 8:00pm realm time using Census addon. This is Horde and Alliance combined. Samples were taken across 33 Retail NA realms.

Average number of concurrent players per realm type:

New Player: 353

Low: 90

Medium: 108

High: 346

Full: 155



Total number of realms:

New Player: 11

Low: 26

Medium: 156

High: 29

Full: 24

If you do all the math it comes out to 27,939 concurrent players.

TLDR:

High realms on Retail have 350 players on them. High realms on Classic have around 12-14k players on them.