The easy path, as someone suggested, is a kill-a-watt that you just plug it into.
The less intrusive path for some definition of less intrusive is a clamp ammeter if you can expose one of the AC wires (you have to clamp around an individual wire, not both hot and neutral). But then you don't need to unplug the system to measure it.
The third overkill option is to have it plugged into a full-time power monitoring and control device, such as a zigbee home automation plug switch. ;)
The less intrusive path for some definition of less intrusive is a clamp ammeter if you can expose one of the AC wires (you have to clamp around an individual wire, not both hot and neutral). But then you don't need to unplug the system to measure it.
The third overkill option is to have it plugged into a full-time power monitoring and control device, such as a zigbee home automation plug switch. ;)