Electrical Tool

Transformer Sizing Tool

Estimate control transformer size for rooftop units, air handlers, panel retrofits, and BAS control cabinets. This tool totals connected VA load and adds spare capacity so you can avoid nuisance undervoltage on startup.

Load Inputs

Controllers / boards qty

VA each

Actuators / relays qty

VA each

Contactors / safety loads qty

VA each

Secondary voltage

Spare capacity (%)

Results

Connected VA

Recommended minimum VA

Secondary current

0 A

Run the calculation to estimate practical transformer capacity for the panel.

Related Tools

Voltage Drop CalculatorCheck the feeder or branch circuit feeding the transformer.BAS Point Count EstimatorEstimate controls scope before loading accessories.Controls Electrical GuideCommon transformer and controls circuit mistakes.