How to size a UPS

You have decided that you need a UPS. What’s next? Well, you have to pick the right one!

Alternative #1:


Alternative #2:

Do it the old fashioned way. Completing these steps is also very useful for the first two alternatives.

1. List all equipment to be protected by the UPS. (Remember to include monitors, external hard drives, routers, etc.)

2. List the amps and volts for each device. These ratings can typically be found on the label on the back of the equipment. Multiply amps by volts to determine VoltAmps (VA). Some devices may list their power requirements in watts. To convert watts to VA, divide the watts by power factor. For servers, the power factor is often 0.9.

3. Multiply the VA by the number of pieces of equipment to get the VA subtotals.

4. Add the VA subtotals together.

5. Multiply the total by 1.2 to get the grand total. This step accounts for future expansion.

6. Use the grand total to select a UPS. When choosing a UPS, be sure that the total VA requirement of supported equipment does not exceed the VA rating of the UPS.

UPS Sizing Worksheet

How to size a UPS