What this calculator does
kVA (kilovolt-amps) measures apparent electrical power, the figure used to size generators, transformers, cables and switchboards, while amps measure the current actually flowing. Converting between the two needs the supply voltage as well, since the same kVA load draws different current depending on whether the system runs at 230V or 400V, and on whether it is single-phase or three-phase.
Three-phase systems need an extra factor of √3 (about 1.732) in the conversion compared with single-phase, because the load is split across three conductors rather than one. Getting single-phase and three-phase mixed up is the most common mistake when sizing equipment from a kVA rating.
The formula
For single-phase supply, amps = (kVA × 1,000) ÷ voltage. For three-phase supply, amps = (kVA × 1,000) ÷ (√3 × voltage), where √3 is approximately 1.732. Converting from amps back to kVA reverses the same formula.
| Term | Meaning |
|---|---|
| kVA | Kilovolt-amps, a measure of apparent power: voltage × current, divided by 1,000. |
| Amps (A) | The electrical current, the rate of charge flow through the conductor. |
| Voltage (V) | The electrical potential of the supply, such as 230V (single-phase) or 400V (three-phase) in many countries. |
| √3 | The square root of 3, approximately 1.732, which accounts for the phase relationship across three conductors in a three-phase system. |
The inputs explained
| Field | What to enter |
|---|---|
| Convert | Whether to convert a kVA figure into amps, or an amps figure into kVA. |
| Supply | Whether the supply is single-phase or three-phase; this changes the formula used. |
| Voltage (V) | The system voltage, such as 230V for single-phase or 400V for three-phase in many regions. |
| kVA (if converting to Amps) or Amps (if converting to kVA) | The kVA value (if converting to amps) or the amps value (if converting to kVA). |
When to use it
Sizing a generator or supply cable
A generator or transformer is usually rated in kVA, but the breakers and cables downstream need a current rating in amps, so this conversion sits directly between the two specifications.
Checking a load against a circuit breaker rating
Converting a piece of equipment's kVA rating to amps at the actual supply voltage confirms whether it fits under the amp rating of the circuit breaker or cable feeding it.
Comparing single-phase and three-phase options
The same kVA load draws noticeably less current per conductor on a three-phase supply than on single-phase, which is one reason larger loads are often run three-phase.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
Amps for a range of kVA loads on a 230V single-phase supply
A range of kVA loads converted to amps at a fixed 230V single-phase supply.
Amps for the same kVA loads on a 400V three-phase supply
The same range of kVA loads, this time on a 400V three-phase supply, for comparison against the single-phase figures above.
Questions
How do I convert kVA to amps?
For single-phase supply, divide (kVA × 1,000) by the voltage. For three-phase supply, divide (kVA × 1,000) by (√3 × voltage). The voltage and phase type both need to be known before the conversion can be done.
Why does three-phase need the √3 factor and single-phase does not?
In a three-phase system the total apparent power is spread across three conductors with a fixed phase relationship between them, and √3 (about 1.732) is the factor that correctly accounts for that relationship when converting between line current and total kVA. Single-phase has only one live conductor, so no such factor is needed.
Is kVA the same as kW?
No. kVA is apparent power (voltage × current); kW is real power, the part that actually does useful work. They are equal only when the power factor is exactly 1; for most real electrical loads, kW is somewhat less than kVA, and the gap is the power factor.
What voltage should I use for a three-phase kVA to amps conversion?
Use the line-to-line voltage of the three-phase supply, such as 400V in many countries with a 230V phase voltage, not the single-phase voltage of one leg. Using the wrong voltage figure is a common source of error in this conversion.
For voltage, current, resistance and power on a simple DC circuit, see the Ohm's law calculator.