How do you calculate the UPS size for 1phase loads?

In the UK and Europe the 1-phase supply is 230Vac at 50Hz. Calculate the load Amps being drawn by the IT devices to be powered from the UPS to give a total Amps and multiply this by the mains supply voltage i.e. 10A x 230Vac = 2300VA or 2.3kVA. It is also worth adding a scaling factor of 20% to allow for future expansion so 2.3kVA x 1.2 = 2.76kVA. The nearest sized UPS system to his would be a 3kVA uninterruptible power supply.