Depending on your set-up, 2-4 people.
On one site, I'd say 6 is the max (2 in the car, 4 in a tent) ... I've never camped with just one site though, so that might be on the high side.
I say 4 comfortably. Take your tent down each morning for more space during the day.
4/10-4/12 Coachella Weekend 1
4/14/15 Cloud Nothings @ Echo
4/17/15 Mac DeMarco @ Ventura Theater
5/01/15 Mikal Cronin, WAND @ CFAER
5/17/15 Ex Hex @ Acerogami
5/25/15 Refused @ Observatory
5/31/15 Neutral Milk Hotel @ Ventura Theater
5/28/15 Mystic Braves w/Mr Elevator & the Brain Hotel @ Soho
6/03/15 Kiasmos @ Masonic Lodge