How to Size a Transformer
Finding the correct kVA rating for your transformer is easy. Follow these instructions to calculate and verify the appropriately sized transformer for your project.
Transformer kVA Calculator
Calculate your transformer's size by filling any two of the fields below.
How to Size a Transformer
1. Identify Load Voltage & Amps
Check your equipment’s nameplate or manual to find the required voltage and amperage. If those aren’t available, your electrician or installer can confirm the numbers, or measure the load directly. Enter these values to get an accurate kVA calculation.
2. Use Calculator to Find kVA Rating
Plug your amps and volts into our kVA calculator to find the minimum size for your transformer. Alternatively, if you already know your kVA rating and want to find amps or volts, you can plug in the two known numbers and the calculator will produce the third.
3. Increase Rating to Prevent Overload
The formula used by this calculator provides the minimum kVA rating based on load amperage and voltage. We recommend sizing your transformer at 120% the minimum kVA to prevent overload and preserve its lifespan.
Minimum rating / 0.8 = Recommended transformer size
4. Consult Qualified Electrician
While this calculator provides accurate sizing information, Maddox recommends you review this information with a licensed electrician or engineer prior to making any purchases or performing any installations.
Transformer Sizing Formulas
The kVA calculator uses the following formulas to calculate the minimum transformer rating for your next project.
Single Phase kVA Formula
To size a transformer for a single phase system, use this formula:
kVA = (Amps x Volts) / 1000
Three Phase kVA Formula
To size a transformer for a three phase system, use this formula:
kVA = (Amps x 1.732 x Volts) / 1000
Definitions
What is Voltage?
Electric potential, measured in volts (V), represents the amount of electrical potential energy per unit charge at a specific point in the circuit. Voltage is the driving force that causes electric charges to move within a circuit.
What are Amps?
Amps, short for amperes, is a unit of electric current. It is a measure of the rate at which electric charges flow through a conductor in an electrical circuit.
What is kVA?
kVA stands for kilovolt-ampere, which is a unit of apparent power in an electrical system. It measures the total power, both real and reactive, in an alternating current (AC) circuit. The symbol for kilovolt-ampere is "kVA."
What is a Transformer?
A transformer is an electrical device that takes a given input voltage and changes it to a different output voltage. This change can either be an increase or a decrease in voltage. Want to know more? Learn what transformers are and how they work here.
Get a Transformer Quote
Maddox stocks thousands of new and remanufactured transformers. Whatever size transformer your project requires–from 5 kVA to 100 MVA–Maddox sells the transformers you need.
