What this calculator does
This tool provides a quick estimate of the transformer kVA rating needed to serve a given electrical load, based on the load’s voltage, current, and phase configuration.
The formula
For a single-phase load, apparent power is S = V × I. For a balanced three-phase load, it’s S = √3 × V × I. A safety margin (commonly 20–25%) is then added to account for load growth, inrush current, and to avoid running the transformer at its absolute limit continuously.
This is a general sizing estimate for planning purposes only. Final transformer selection should account for ambient temperature, duty cycle, harmonics, and applicable electrical codes, and should be confirmed by a qualified electrical engineer.
Last reviewed August 2026