hi, may i know why need to calculate requirement based on VA? iinm the VA value is wattage required plus any imperfections in the equipment power factor due to capacitance/inductance. usually i will choose any VA as long as its higher than my PSU rating.

afaik the most important UPS rating is the battery AH (amp-hour) value. so if you need 1000W with 240V mains supply, your current draw will be roughly 4 amps. so for example if the blackout lasts for 1 hour you will need at least a UPS with 4AH battery capacity.