How do I calculate how much power my USB hub needs

My understanding is that each USB port is only capable of providing so much power. Currently I have plenty of USB ports available and my reason for considering the purchase of a

PLUGABLE USB 3.0 7-PORT HUB WITH 25W POWER ADAPTER
http://plugable.com/products/usb3-hub…

is for simplicity. I want to be able to unplug my 6 USB graphics adapters all at once and simply plug them into a different terminal. How do I calculate how many watts I need my usb hub to have in order to power 6…

Plugable USB 3.0 to VGA / DVI / HDMI Video Graphics Adapter
http://www.amazon.ca/gp/product/B00A2…

Thank you

Hello,

Our 7-port USB3-HUB7-81X should be able to power 6 of our UGA-3000 graphics adapters without issue, however, please be aware some systems may have trouble with that many USB devices being attached.

See here for more information: http://plugable.com/2015/09/08/not-en…

Thanks!