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kVA to Amps Calculator

Transformer kVA to full load amps, single or three phase.

Your measurementsEvery assumption editable01
Full load currentCalculated live02

Result

124.9A

45 kVA at 208 V three phase

Apparent power45000 VA
45 kVA
Line voltage
208 V
Phase
Three phase
Full load currentkVA × 1000 ÷ (√3 × V)
124.91 A
Real powerat 0.9 power factor
40.5 kW

The √3 in the three-phase formula is not a fudge factor — it falls out of the 120-degree phase relationship between the legs. Using the single-phase formula on a three-phase system overstates the current by about seventy-three per cent.

Transformers are rated in kVA rather than kW precisely because apparent power is what heats the windings. The real power delivered depends on the load's power factor, which the transformer neither knows nor controls.

This gives full-load current. Overcurrent protection on both the primary and secondary sides has its own sizing rules that depend on the transformer and the code in force.

Enter the transformer rating, line voltage and phase. The √3 in the three-phase formula is not a fudge — it falls out of the 120-degree relationship between the legs, and using the single-phase formula instead overstates current by about 73%.

Why use this tool?What it does differently03

Why use this tool?

Both phase configurations

Single and three phase, with the correct formula applied to each.

Real power too

kW alongside kVA at whatever power factor you enter.

Explains the √3

It comes from the phase relationship, not from a correction factor someone invented.

Protection flagged

Full load current is not the same as overcurrent protection sizing.

How this worksThe method04

How this kva to amps calculator works

For single phase, full load current is volt-amps divided by voltage. For three phase, it is volt-amps divided by the product of √3 and the line voltage.

That √3 arises from the geometry of three-phase power, where the legs are 120 degrees apart. Applying the single-phase formula to a three-phase system overstates current by roughly seventy-three per cent — a large and common error.

Transformers are rated in kVA rather than kW because apparent power is what heats the windings. How much real power reaches the load depends on the load's power factor, which the transformer neither knows nor controls.

How to use itStep by step05

How to use it

  1. Step 1: Enter the kVA rating

    From the transformer nameplate.

  2. Step 2: Enter line voltage

    The line-to-line voltage on the side you are calculating.

  3. Step 3: Select the phase

    Single or three phase — this changes the formula, not just a constant.

  4. Step 4: Set the power factor

    For the real power figure. It does not affect full load current.

Example usageWorked figures06

Example usage

A three-phase transformer
45 kVA at 208 V three phase gives 124.9 A full load. At 0.9 power factor that is 40.5 kW of real power.
The same rating, single phase
45 kVA at 240 V single phase gives 187.5 A — considerably higher current for identical apparent power.
A larger unit
150 kVA at 480 V three phase gives 180.4 A. Higher voltage keeps current manageable as capacity grows.
Frequently asked questionsCommon questions07

Frequently asked questions

How do I convert kVA to amps?

Single phase: kVA × 1000 ÷ voltage. Three phase: kVA × 1000 ÷ (√3 × voltage). The √3 is roughly 1.732.

What is the difference between kVA and kW?

kVA is apparent power, kW is real power, and power factor is the ratio between them. A 100 kVA transformer delivers 90 kW to a load with a 0.9 power factor.

Why is there a √3 in three-phase formulas?

It comes from the 120-degree phase relationship between the three legs. It is geometry, not a correction factor.

Why are transformers rated in kVA rather than kW?

Because apparent power determines winding heating regardless of the load's power factor. The transformer cannot know how much useful work the load extracts.

Does this size the overcurrent protection?

No. Primary and secondary protection have their own sizing rules that depend on the transformer and the code in force locally.

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