Physics

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AC Wattage Calculator.

Calculate single-phase apparent AC power from RMS voltage and current.

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Apparent power: 1,200

Apparent power

1,200.000000

Educational physics model using the stated SI assumptions; verify engineering and safety decisions independently.

Use Cases

Electrical Load Assessment

Quickly estimate the apparent power requirement of a single-phase appliance or circuit to ensure proper wiring and breaker sizing.

Example: A heater draws 10 A at 230 V, giving 2300 VA.

Transformer Sizing

Determine the VA rating needed for a transformer supplying a single-phase load, ensuring it can handle the total apparent power.

Example: A load of 5 A at 120 V requires a 600 VA transformer.

Frequently Asked Questions

What does this AC wattage calculator do?
It calculates the apparent power (in volt-amperes, VA) for a single-phase AC circuit using the RMS voltage (V) and RMS current (A) you input. The result is the product of these two values, representing the total power drawn from the source.
Why is apparent power different from real power?
Apparent power (VA) is the product of RMS voltage and current, while real power (watts) also accounts for the phase difference (power factor) between them. This calculator provides apparent power, which is useful for sizing wires and transformers, but real power may be lower if the load is reactive.
Can I use this for three-phase systems?
No, this calculator is specifically for single-phase AC circuits. For three-phase systems, you would need a different formula that includes the square root of 3 and possibly line-to-line or line-to-neutral voltages.

Tips & Common Mistakes

Tips

  • Use RMS values for voltage and current, not peak values, to get accurate apparent power.
  • For purely resistive loads, apparent power equals real power in watts, but for reactive loads, real power is less.
  • Always double-check your units: voltage in volts (V) and current in amperes (A) to get VA.
  • If you have the power factor, you can convert VA to watts by multiplying by the power factor.

Common Mistakes to Avoid

  • Using peak voltage or current instead of RMS values, which overestimates the apparent power.
  • Confusing apparent power (VA) with real power (W) when the load is not purely resistive.
  • Applying this single-phase calculator to three-phase systems without proper conversion.

Last updated: August 13, 2026