That's confusing because USB 3 hubs are 12 volts I thought.
Would be the Amps that determine how many you can run.
all usb hubs put out 5 volts the usb port, but they have different input power bricks.. if the hub has a 5 volt brick there is no dc to dc converter in it. if a HUB has a 12 volt brick there is a 12 volt to 5 volt dc to dc converter in it. general rules of thumb a 12 volt brick when converted to 5 volts keeps 80 percent of the power. so 12 volt x 5 amp = 60 watts x 80 percent or 48 watts. safe 24/7/365 run is at 80 percent so 80 percent time 48 = 38.4 watts to 3.84 watts for 1 of 10 ports.
a 5 volt hub is 5 volts x ? amps .. I have a few that are 4 amps so 5 x 4 = 20 watts at 24/7/365 x 80 percent = 16 watts so if this is for a 7 port hub it is a no go as 16 /7 = 2.2 watts a port which is not enough.
I am assuimng the bricks run to their ratings. most don't
never never never stick a 12 volt hub brick into a 5 volt hub .. you will fry the hub and the sticks/ been there done that.
here is a 7 port hub with a 5 volt 4 amp brick it runs 3 or 4 sticks:
http://www.amazon.com/GearMo%C2%AE-3DH-USB-3-0-7-Port/dp/B00BZABE72/ref=sr_1_3?ie=UTF8&qid=1386466199&sr=8-3&keywords=gearmo+7+porthere is a 10 port hub with a 12 volt 4 amp hub
http://www.gearmo.com/shop/10-port-usb-3-hub-gm-3dh10/ this runs around 6 sticks. if you take this hubs brick and stick it in the 7 port hub from the same company you will burn up the 7 port hub.
I had hundreds of am sticks and around 20 -25 hubs I learned one lesson don't mix hubs make sure every one is a 5 volt power brick or a 12 volt power brick.. this way you can't burn the gear up