kVA to amps converter
Converting kVA to amps gives the full-load current of equipment rated in kilovolt-amperes, such as a transformer, generator or UPS, from its rating and voltage alone. No power factor is involved, because kVA already includes both the real and reactive parts of the load.
Convert kVA to amps
Updates as the values change. The page address keeps the values for sharing.
Transformer nameplates list a kVA rating and two voltages, primary and secondary. Converting the rating at each voltage gives the full-load current on each side, the starting point for selecting conductors and protection under NEC 450.3 and 240.21(C).
Formulas
Single phase AC
Pad-mount and pole-mount transformers serving homes are single phase, usually with a 120/240 V secondary; the current on each secondary leg is the kVA rating divided by 240 V.
Three phase AC
Dry-type building transformers such as 480 V to 208Y/120 V units are three phase; the current is the same in each line at full load.
Apparent power in kVA times 1,000 gives volt-amperes. Because kVA is not reduced by power factor, the full-load current is the same whatever the load's power factor; only the usable kW changes.
Worked examples
A 25 kVA single-phase transformer with a 120/240 V secondary
A typical residential distribution transformer; the secondary current is found at 240 V.
I = kVA × 1,000 ÷ VI = 25 kVA × 1,000 ÷ (240 V) = 104.17 A
The full-load secondary current is 104.17 A on each leg.
A 75 kVA, 480 V to 208Y/120 V dry-type transformer
The same rating converted at each winding voltage gives the primary and secondary currents.
I = kVA × 1,000 ÷ (√3 × V(L-L))I = 75 kVA × 1,000 ÷ (1.732 × 208 V) = 208.18 A
Secondary full-load current is 208.18 A at 208 V; the primary carries 90.21 A at 480 V. The ratio of the currents is the inverse of the voltage ratio.
A 150 kVA standby generator at 480Y/277 V, entered as 277 V line to neutral
The generator data sheet lists 277 V to neutral; the converter works out the 480 V line-to-line value.
V(L-L) = √3 × V(L-N) = 1.732 × 277 V = 479.78 VI = kVA × 1,000 ÷ (√3 × V(L-L))I = 150 kVA × 1,000 ÷ (1.732 × 479.78 V) = 180.51 A
The generator's rated output current is 180.51 A per line.
Conversion table
| kVA (kVA) | 120 V single phase (A) | 240 V single phase (A) | 208 V three phase (A) | 480 V three phase (A) |
|---|---|---|---|---|
| 3 | 25.0 | 12.5 | 8.3 | 3.6 |
| 5 | 41.7 | 20.8 | 13.9 | 6.0 |
| 10 | 83.3 | 41.7 | 27.8 | 12.0 |
| 15 | 125.0 | 62.5 | 41.6 | 18.0 |
| 25 | 208.3 | 104.2 | 69.4 | 30.1 |
| 30 | 250.0 | 125.0 | 83.3 | 36.1 |
| 37.5 | 312.5 | 156.3 | 104.1 | 45.1 |
| 45 | 375.0 | 187.5 | 124.9 | 54.1 |
| 50 | 416.7 | 208.3 | 138.8 | 60.1 |
| 75 | 625.0 | 312.5 | 208.2 | 90.2 |
| 100 | 833.3 | 416.7 | 277.6 | 120.3 |
| 112.5 | 937.5 | 468.8 | 312.3 | 135.3 |
| 150 | 1,250.0 | 625.0 | 416.4 | 180.4 |
| 225 | 1,875.0 | 937.5 | 624.5 | 270.6 |
| 300 | 2,500.0 | 1,250.0 | 832.7 | 360.8 |
| 500 | 4,166.7 | 2,083.3 | 1,387.9 | 601.4 |
Generated by the converter's engine. Single-phase and three-phase columns apply to equipment of that type; a three-phase rating is not converted with the single-phase column.
Common mistakes
Applying a power factor to a kVA rating
Multiplying or dividing a kVA rating by a power factor before converting to current double-counts it. Full-load current comes from kVA and voltage alone; power factor only matters when converting to kW.
Using the secondary voltage for the primary current
A 480 V to 208 V transformer's primary current is about 43% of its secondary current. Converting at the wrong winding's voltage leads to conductors sized for the other side of the transformer.
Treating full-load amps as the protection rating
Transformer overcurrent protection under NEC 450.3 is a percentage of rated current that depends on voltage class and whether secondary protection is provided. The converted current is the base for that calculation, not its result.
Using 120 V for a 208Y/120 V three-phase unit without the selector
Dividing by √3 × 120 V instead of √3 × 208 V returns 1.73 times the real current. The voltage selector set to line to neutral handles 120 V and 277 V ratings correctly.
Frequently asked questions
How many amps is a 75 kVA transformer at 208 V?
A 75 kVA three-phase transformer has a full-load current of 208.18 A at 208 V and 90.21 A at 480 V.
How many amps does a 25 kVA single-phase transformer supply at 240 V?
104.17 A on each leg of the 120/240 V secondary at full load.
Why is no power factor needed for kVA to amps?
Current depends on apparent power, which kVA already is. The power factor only splits that apparent power into real power (kW) and reactive power (kVAR).
How many amps is 1 kVA?
1 kVA is 8.33 A at 120 V and 4.17 A at 240 V single phase, or 2.78 A at 208 V three phase.
Does the full-load current set the transformer's breaker size?
Not directly. NEC 450.3 sets maximum protection as a percentage of rated current, and secondary conductors follow 240.21(C). The transformer sizing calculator and breaker size calculator help with those steps.