As part of that machine's UL listing, there should be a "nameplate" AC power draw (which it draws from the AC side, not what it produces). you rely on that nameplate number, which is either in amps or VA, when determining how many an AC circuit can handle.
VA is sister to "watts" -- simply put, watts are the part of the sinewave your load actually uses, and VA is the entire sinewave.
It is acceptable to measure the device's actual power draw at max load (assuming it is consistent) using a monitoring tool like a Kill-A-Watt, and use that number instead of nameplate.
Now if the load will be a contiuous load (>3 hours), you must do a derate - and that is 125%. Meaning if the machine nameplates at 800VA, you must derate it, counting it as if it is 1000VA. That applies against the 4400VA capacity of your 20A, 220V circuit.
Be careful not to double-derate, for instance I was looking at a 30A Tripp-Lite PDU that admonished users not to exceed 24A. That is the same derate.
That 125% is your design margin. It is the only margin you are required to have.
Inrush current is no big deal, the AC power system is already factored to cope with it, since it is also done by motors, incandescent lights, and almost any modern switching supply including electronic ballasts and LED drivers.