Transformer kVA
Calculator
Calculate transformer size from load voltage and current — or solve for any of the three values. Toggle between single-phase and three-phase formulas.
Sizing a Transformer in 4 Steps
Check your equipment's nameplate or engineering drawings. The required voltage and full-load current are the two inputs needed to calculate transformer kVA.
Toggle between 1-Phase (single-phase) and 3-Phase (three-phase) to apply the correct formula. Three-phase calculations include the √3 (≈ 1.732) multiplier.
Enter any two known values and calculate the third. The result is the minimum kVA rating for your load at those conditions.
Size up to the next standard transformer rating above your minimum. We recommend specifying 125% of minimum kVA (÷ 0.8) to provide headroom and preserve transformer life.
Enter any two of the three values (Volts, Amps, or kVA) and leave the third field blank. Click Calculate to solve for the missing value. Works for both single-phase and three-phase systems.
The calculated kVA is the minimum rating at your load conditions. We recommend specifying a transformer at approximately 125% of the calculated minimum (divide by 0.8) to prevent overloading and preserve service life. Standard transformer sizes are discrete (15, 25, 37.5, 50, 75, 100, 167, 250, 333, 500 kVA, etc.) — choose the next standard size above your calculated value.
No — this calculator computes apparent power (kVA), which is the product of voltage and current. Power factor affects how much of this apparent power is real power (kW). Use our kW to kVA Calculator to convert between real and apparent power when you know your load's power factor.
For a single-phase system: kVA = (V × A) / 1,000. For a three-phase system, the current flows in three conductors at different phase angles, so the formula includes √3 (≈ 1.732): kVA = (V × A × √3) / 1,000. The three-phase voltage used in this calculator is the line-to-line voltage, not the phase voltage.
Ready to Order Your Transformer?
Once you have your kVA and voltage requirements, our engineering team can provide a specification, lead time, and price the same day.