UPS VA v Amps v Watts Comparison and Sizing Table

This table covers single phase UPS loads from 250VA to 10kVA and shows the Amps drawn at 230Vac, 50Hz (the UK single phase supply). To select the right UPS system for your load, calculate the VA, Amps or Watts and then select a suitable UPS size/model from our ranges.

Note:^ the more you oversize a UPS, the longer the battery will provide backup runtime for.

If you want to calculate the VA then see our UPS sizing formulae.

Understanding The Difference Between VA and Watts

Uninterruptible power supplies (UPS) are typically shown in sizes expressed in VA (or kVA = 1000VA).

VA is referred as to as the Apparent Power and is calculated from multiplying the Amps drawn by the load, by the voltage of the single phase supply the load is powered from (typically 230Vac, 50Hz in the UK).

In the first row of the table above 250VA is 1.09Amps at 230Vac = 1.09Amps x 230Vac = 250VA.

Real Power is measured on Watts (or kW) and is measure of the energy consumed by a load. Apparent Power and Real Power are related by a ratio figure, refered to as the Power Factor.

From the table each of the VA load sizes has a corresponding Watt rating based on a power factor. If we want to know the Watt rating of the load we have to know the power factor or measure the load demand in Watts of the devices. Most modern electronic power supplies run at unity power factor (PF=1) or (PF=0.9). In the example, the load is 250VA or 1.09Amps or 250W at unity power factor or 225W at 0.9pF. Older computers and PCs typically had poor power factors of 0.6 to 0.7pF.

Most UPS at 10kVA and below are selected based on their VA or kVA rating. We also recommened oversizing a UPS system so that it runs at or neat to 80% of its VA or kVA rating. This allows some room for expansion and also increases the runtime from the battery set from that it would be at full load.

For more information on UPS sizing please contact us.