kVA to Amps Calculator

A kVA to amps calculator turns an apparent-power rating into the line current a circuit will actually carry. The rule is short: divide by the voltage on a single-phase circuit, and by 1.732 times the voltage on a three-phase circuit. A 75 kVA transformer at 480 V three-phase draws 90.2 amps; the same 75 kVA at 208 V three-phase is 208.2 amps.

Three neighboring tools handle the rest of the circuit. The Watts to Amps Calculator starts from real power in watts when the nameplate gives no kVA, the Ohm's Law Calculator moves between volts, amps, ohms and watts on a simple resistive circuit, and the Voltage Drop Calculator takes the amps you get here and tells you whether the run length forces a bigger conductor. Use this page whenever the rating in front of you is written in kVA - transformers, generators, UPS units and switchgear almost always are.

How the kVA to amps conversion works

Apparent power (symbol S, unit volt-amperes) is simply voltage multiplied by current. Rearranged for current, and with kVA converted to VA by multiplying by 1,000, the two formulas are:

where I is the line current in amps, S is the apparent power in kVA and V is the voltage in volts (line-to-line for three-phase). The √3 factor, 1.7320508, appears because a balanced three-phase system carries a total apparent power of √3 × V_line × I_line. Notice what is missing: the power factor. Because kVA already contains both volts and amps, no power factor is needed to get the current. Power factor only enters when you want kilowatts.

Worked example: a 75 kVA three-phase transformer

A 75 kVA dry-type transformer feeds a shop from a 480 V three-phase panel and steps it down to 208Y/120 V for receptacles and small machines. You need both currents to size the primary and secondary conductors.

• Primary at 480 V: 1000 × 75 ÷ (1.732 × 480) = 75,000 ÷ 831.4 = 90.2 amps
• Secondary at 208 V: 1000 × 75 ÷ (1.732 × 208) = 75,000 ÷ 360.3 = 208.2 amps
• Continuous-load check (primary): 90.2 × 1.25 = 112.8 amps
• Real power at PF 0.80: 75 × 0.80 = 60.0 kW, with 45.0 kVAR of reactive power

The kVA is identical on both sides of the transformer, yet the secondary current is 2.31 times the primary current because 480 divided by 208 is 2.31. That ratio is the whole reason distribution runs at higher voltage: the same power moves with less current, so the conductors can be smaller and the losses lower.

Worked example: 10 kVA single-phase at 240 V

A 10 kVA single-phase control transformer sits on a 240 V feeder. Single-phase drops the √3, so the arithmetic is even simpler: 1000 × 10 ÷ 240 = 41.7 amps. At 120 V the same 10 kVA would be 83.3 amps, exactly double, because halving the voltage doubles the current. Multiplied by the 1.25 continuous factor, the 240 V figure becomes 52.1 amps.

Running it backwards proves the formula: 240 × 41.67 ÷ 1000 = 10.0 kVA. And if the nameplate had listed 9.5 kW instead at a power factor of 0.95, the apparent power would be 9.5 ÷ 0.95 = 10 kVA and the current identical.

kVA to amps chart: three-phase

Line current for standard transformer sizes on balanced three-phase systems, computed with I = 1000 × kVA ÷ (1.732 × V):

Every column scales in a straight line, so you can read any rating off the chart: at 480 V three-phase each kVA is 1.203 amps, at 240 V it is 2.406 amps, and at 208 V it is 2.776 amps. A 60 kVA unit at 480 V is therefore 60 × 1.203 = 72.2 amps.

kVA to amps chart: single-phase

The same conversion without the √3, for single-phase transformers, welders, UPS units and 120/240 V services:

Compare the two charts and the √3 advantage is obvious: 100 kVA at 240 V is 416.7 amps single-phase but only 240.6 amps three-phase, a 42% reduction in current for identical power.

Amps to kVA chart

Going the other way, from a breaker or service size to the apparent power it represents, uses kVA = V × A ÷ 1000 single-phase and kVA = 1.732 × V × A ÷ 1000 three-phase:

Values are in kVA. A typical 200 amp 240 V residential service is 48 kVA of connected capacity, and a 400 amp 480 V three-phase service is 332.6 kVA.

kVA, kW and power factor

Apparent power and real power are not interchangeable. kVA is the vector sum of the working current and the magnetizing current, and it is what the copper, the breaker and the transformer core have to handle. kW is only the part that turns into torque, heat or light. The link is the power factor:

Motor and generator ratings usually assume a power factor of 0.8, resistive heaters are close to 1.0, and modern electronic power supplies with correction land near 0.95. The table below applies both directions to a 100 unit load and shows the resulting 480 V three-phase current:

Dropping from a power factor of 1.0 to 0.7 raises the current for the same useful 100 kW by 43%, which is why utilities bill large customers for poor power factor and why correction capacitors pay for themselves.

How to use this kVA to amps calculator

1. Pick the direction: kVA to amps for a nameplate rating, Amps to kVA to work back from a breaker or measured current, or kW to amps when the equipment is rated in kilowatts.
2. Choose the phase: single-phase for 120 V and 120/240 V circuits and small transformers, three-phase for 208 V, 240 V, 480 V and 600 V distribution.
3. Set the voltage: tap one of the six presets or type any value, such as 415 V or 208 V measured at 202 V. Use the line-to-line voltage for three-phase.
4. Enter the rating: type the kVA, the amps or the kW. Quick-pick buttons cover the standard transformer sizes and common breaker ratings.
5. Set the power factor if you care about the kW figure, or if you are converting from kW. Leave it at 0.80 for motors, raise it to 1.00 for resistive heat.
6. Read the result: the headline gives amps (or kVA in reverse mode), and the tiles below show apparent power, real power, the current multiplied by 1.25 for continuous loading, and the same load compared across all six standard voltages.

Who this calculator is for

• Electricians and estimators reading a transformer or switchgear nameplate and needing the full-load current before they pick conductors.
• Facility and maintenance managers checking whether an existing panel has room for a new machine.
• Generator and UPS buyers translating a kVA quote into the amps their transfer switch and feeders must carry.
• Solar, EV-charging and data-center installers sizing service capacity in kVA and reporting it to the utility in amps.
• Apprentices and engineering students practicing the √3 relationship until it is second nature.
• Homeowners with a standby generator converting a kW rating into the amperage the interlock and inlet must support.

Key terms explained

• Apparent power (kVA): volts times amps, divided by 1,000. The rating that sizes wire, breakers, transformers and generators.
• Real power (kW): the portion that does useful work. Always equal to or less than the kVA.
• Reactive power (kVAR): the magnetizing power stored and returned each cycle by motors and transformers. It carries current without doing work.
• Power factor: kW divided by kVA, between 0 and 1. A lagging power factor is typical of inductive loads such as motors.
• Line current: the current in each ungrounded conductor. In a balanced three-phase circuit all three are equal, which is what the formula assumes.
• Line-to-line voltage: the voltage between any two phase conductors, 208 V or 480 V in typical US systems. Line-to-neutral is that value divided by 1.732, giving 120 V and 277 V.
• Full-load amps (FLA): the current at the rated output shown on the nameplate. It is what this calculator produces.

What changes the answer

• Voltage: the biggest lever. Current is inversely proportional to voltage, so moving a 100 kVA load from 208 V to 480 V three-phase cuts the current from 277.6 amps to 120.3 amps.
• Phase count: switching the same kVA and voltage from single-phase to three-phase divides the current by 1.732.
• The voltage you actually measure: a nominal 480 V system running at 465 V raises the current for a fixed kW load by about 3%.
• Power factor: irrelevant for kVA to amps, decisive for kW to amps. At 0.7 instead of 0.9 the same kilowatts pull 29% more current.
• Load balance: the three-phase formula assumes equal current in all three lines. An unbalanced panel can put substantially more current in one phase than the calculation suggests.

From amps to a conductor and a breaker

The calculated current is the starting point of the sizing chain, not the end of it. Loads that run for three hours or more at a time are treated as continuous, and the branch circuit or feeder is sized at 125% of that current, which is why the calculator prints the 1.25 figure next to the raw amps. From there the conductor still has to pass three more tests: ampacity at the correct termination temperature rating, derating for ambient temperature and for more than three current-carrying conductors sharing a raceway, and voltage drop over the length of the run. On a 90.2 amp feeder the continuous figure is 112.8 amps, so a 125 amp overcurrent device is the natural next standard size, but a 300 foot run or a hot mechanical room can still push the conductor a size or two larger. Check the raceway with the Conduit Fill Calculator and the run length with the Voltage Drop Calculator before you buy wire.

Practical tips

• Memorize the constants instead of the whole chart: at 480 V three-phase, amps are roughly 1.2 times the kVA; at 208 V three-phase, roughly 2.8 times; at 240 V single-phase, roughly 4.2 times.
• On a transformer, run the calculation twice, once per winding. The kVA is the same on both sides; only the current differs.
• When a generator is advertised in both kW and kVA, the ratio between them is its assumed power factor. A 20 kW / 25 kVA set assumes 0.8.
• Use the line-to-line voltage for three-phase. Entering 277 V with the three-phase mode selected will understate the current by a factor of 1.732.
• For a UPS, watch which rating limits you. A 10 kVA / 8 kW unit cannot deliver 10 kW no matter how good your load's power factor is.

Limitations and assumptions

• The three-phase formula assumes a balanced load with equal current in all three lines and a sinusoidal waveform.
• Harmonic-rich loads such as variable frequency drives and large rectifier banks raise the true root-mean-square current above this figure and can overload a shared neutral.
• Transformer inrush and motor locked-rotor current are many times the full-load value and govern protection settings, not this calculation.
• Transformer losses mean the primary draws slightly more than the secondary delivers; the nameplate kVA is the output rating.
• The 1.25 continuous factor shown is a planning multiplier. Actual overcurrent and conductor sizing must follow the adopted code, the termination ratings and the authority having jurisdiction.

How it compares to related calculators

This page answers "how many amps is this kVA rating?" If your question is slightly different, a sister tool fits better:

• If the nameplate is in watts rather than kVA, use the Watts to Amps Calculator.
• For volts, amps, ohms and watts on a simple circuit, use the Ohm's Law Calculator.
• To check whether a long run needs a heavier conductor, use the Voltage Drop Calculator.
• To confirm the conductors physically fit the raceway, use the Conduit Fill Calculator.
• To turn kilowatt-hours into a monthly bill, use the Electricity Cost Calculator.
• For heating and cooling capacity in a room, use the BTU Calculator.

Sources

• National Institute of Standards and Technology (NIST) - SI units: the volt-ampere, the watt and the var as the units of apparent, real and reactive power. The conversion itself is a definition, so no rate or market assumption enters it.
• National Fire Protection Association (NFPA) - NFPA 70, National Electrical Code (NEC): Articles 210.19, 215.2 and 215.3 for the 125% continuous-load factor applied to branch circuits, feeders and their overcurrent devices, and Article 450 for transformer protection.
• NEC Article 240.6 - the standard ampere ratings of fuses and inverse-time circuit breakers used when the continuous figure is rounded up to the next device size.
• U.S. Department of Energy - Electric motors and distribution transformers: nameplate ratings, full-load current and the role of power factor in motor-driven systems.