When sizing a transformer, you will usually see the capacity listed in kVA.
kVA means kilovolt-amperes.
It is the rating used to show how much electrical capacity a transformer can handle.
What Does kVA Mean?
The letter k means one thousand.
The letters VA mean volt-amperes.
So:
1 kVA = 1,000 VA
For example:
25 kVA = 25,000 VA
A 25 kVA transformer is rated to handle up to 25,000 volt-amperes of load capacity under its rated conditions.
Why Transformers Use kVA Instead of kW
Transformer capacity is based on voltage and current.
That is why transformers are rated in kVA instead of only kilowatts, also called kW.
The kVA rating gives you the transformer capacity needed to handle the electrical load.
Before choosing a transformer, you need to know:
- Load voltage
- Load current in amps
- Whether the load is single-phase or three-phase
Those values are used to calculate the required kVA.
Quick Single-Phase Example
Say you have a 240V single-phase load drawing 80 amps.
240 volts × 80 amps = 19,200 VA
19,200 VA ÷ 1,000 = 19.2 kVA
The load requires at least:
19.2 kVA
Since 19.2 kVA is not a standard transformer size, move up to the next transformer size that can handle the load.
Recommended transformer size = 25 kVA
Quick Three-Phase Example
Three-phase transformer sizing uses a different formula.
Volts × amps × 1.732 ÷ 1,000 = kVA
Say you have a 208V three-phase load drawing 50 amps.
208 volts × 50 amps × 1.732 = 18,012.8 VA
18,012.8 VA ÷ 1,000 = 18.0 kVA
The load requires at least:
18.0 kVA
Move up to the next standard transformer size.
Recommended transformer size = 25 kVA
How Sparky Toolbox Helps
The Sparky Toolbox Transformer Sizing Calculator can calculate both single-phase and three-phase loads.
Enter the voltage, load current, and phase. The calculator shows:
- Required kVA to meet the load demand
- Recommended transformer kVA size
That gives you a quick starting point before selecting equipment or building a material list.
Important Reminder
Transformer kVA is only one part of equipment selection. Final transformer selection can also depend on continuous loads, motor starting current, future load, system voltage, manufacturer ratings, installation conditions, available fault current, and project requirements.
Always verify equipment data, approved plans, manufacturer instructions, and local requirements before installation.