Transformer Sizing Calculator
Estimate the minimum transformer capacity from load current and voltage, then include spare capacity to plan a suitable transformer rating.
Choose the transformer phase and enter the load current and voltage. Results update automatically as you change the inputs.
Transformer Capacity
Transformer capacity is estimated from voltage and current.
How to Use the Calculator
- Select single-phase or three-phase according to the supply system.
- Enter the load current and voltage. Choose A or mA, and V or kV, as appropriate.
- Set the spare capacity percentage to account for planned growth or additional headroom.
- Review the minimum kVA, capacity with spare, and recommended standard transformer rating.
Assumptions and Limitations
This calculator estimates apparent power from voltage and current. For three-phase systems, voltage must be line-to-line. The estimate assumes balanced three-phase loading and does not account for harmonics, inrush current, ambient temperature, altitude, cooling method, impedance, voltage regulation, or local code requirements. The standard rating suggestion is a planning aid, not an equipment specification. Have a qualified electrical professional verify the transformer selection.
