01
Formula
kVA = phase factor × volts × amps × power factor ÷ 1,000.
Required kVA is 1.25 times the load when duty is continuous. The transformer sizing calculator then picks the smallest listed size that covers it.
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Transformer sizing calculator for the next standard kVA
This transformer sizing calculator turns volts and amps into kilovolt-amps, adds 25 percent when the load is continuous, and steps up to the next common standard size. It is a planning sketch, not a short-circuit study.
Duty
Next standard size
112.5kVA
Load74.82 kVA
Required after duty93.53 kVA
PhaseThree
Planning estimate from the numbers you enter. Coverage, density, waste and price are assumptions, not a supplier quote or an engineering specification.
How it works
Three-phase kVA uses the square root of 3.
Three-phase kilovolt-amps equal the square root of 3 times volts times amps times power factor, divided by 1,000. Single phase drops the square root of 3. A continuous load is then multiplied by 1.25. Four hundred eighty volts, 100 amps, three phase, and a 0.90 power factor is about 74.8 kVA. With the continuous adder that is about 93.5 kVA, and the next size in this list is 112.5 kVA. The list runs 15, 30, 45, 75, 112.5, 150, 225, 300, 500, 750, and upward. Temperature, altitude, and harmonics are not in the number.
02
Example
480 volts, 100 amps, three phase, power factor 0.90, continuous.
Load is about 74.8 kVA. Required is about 93.5 kVA. The suggested size is 112.5 kVA. Turn the continuous adder off and the required value falls back to the load.
03
Tips
Power factor is a decimal here.
Type 0.90, not 90. A power factor of 1 sizes the transformer as if real power equals apparent power. Motors usually need the lower factor.
04
Equipment
The transformer and the gear are the purchase.
Dengaro arranges financing for electrical equipment. The kVA is not a loan amount.
Important questions
Know what to expect.
Why add 25 percent?+
A common planning rule sizes a continuous load at 125 percent. Turn it off when the load is not continuous. This is not a permit by itself.
What if my kVA is above 3,000?+
The page reports the required kVA itself when it passes the last size in the list. Confirm that with a supplier.
Is this the inrush size?+
No. Motor starting is not in this transformer sizing calculator. It is the running load.
How do I switch to single phase?+
Choose single phase. The square root of 3 drops out of the formula.
Financing built into the sale