AC VA From Voltage And Current Calculator

The AC VA From Voltage And Current Calculator determines single-phase AC apparent power by multiplying RMS voltage by RMS current. It reports apparent power in volt-amperes (VA), without applying a power-factor adjustment.

For a 120 V load drawing 10 A, the calculator returns 1200 VA. That value is commonly used during preliminary load review, equipment comparison, transformer and UPS planning, and evaluation of AC loads whose power factor has not been established.

Apparent power is not the same as watts. VA expresses the voltage-and-current demand seen by the supply, while watts express real power consumed or converted to useful work. A motor, transformer, electronic power supply, or other inductive or nonlinear load can draw a VA value higher than its real-power wattage.

RMS Voltage and RMS Current

Alternating-current voltage and current continually change magnitude and polarity. The calculation uses RMS voltage and RMS current, which are the effective AC values used for normal electrical system calculations.

Enter these field values:

Input	Unit	Electrical meaning
RMS voltage	V	The effective line voltage applied to the single-phase load
RMS current	A	The effective current drawn by the load
Apparent power	VA	The calculated product of RMS volts and RMS amps

For a nominal 120 V branch circuit, the measured voltage at the load may differ from 120 V because of supply variation, conductor impedance, connection conditions, and voltage drop. When evaluating actual operating demand, use measured RMS values rather than nominal nameplate values where practical.

Single-Phase VA Formula

The calculator applies the following apparent-power equation:

\(\displaystyle S = V_{\mathrm{RMS}} \times I_{\mathrm{RMS}}\)

Or, in abbreviated form:

\(\displaystyle S = V \times I\)

Where:

• S = apparent power in VA
• V = RMS voltage in volts
• I = RMS current in amperes

No power factor is used. The result therefore represents apparent power, not real power in watts.

For loads with known power factor, real power is calculated separately:

\(\displaystyle P = V \times I \times \mathrm{PF}\)

Where P is real power in watts and PF is power factor. Do not treat the calculator’s VA output as watts unless the load has a power factor of 1.0.

Calculation Example

A single-phase load is supplied at 120 V RMS and draws 10 A RMS.

Calculator field	Value
RMS voltage	120 V
RMS current	10 A

\(\displaystyle S = 120 \mathrm{V} \times 10 \mathrm{A} = 1{,}200 \mathrm{VA}\)

\(\displaystyle S = 1{,}200 \mathrm{VA}\)

The displayed results are:

Result	Value
Apparent power	1200 VA
Voltage used	120 V
Current used	10 A

If the load’s power factor were later identified as 0.80, its approximate real power would be:

\(\displaystyle P \approx 1{,}200 \mathrm{VA} \times 0.80 = 960 \mathrm{W}\)

The calculator does not make that power-factor adjustment; it reports the 1200 VA apparent-power value.

Electrical Uses of Apparent Power

VA is useful when evaluating equipment and distribution-system loading based on voltage and current rather than measured wattage.

Common applications include:

• Reviewing the apparent demand of a single-phase branch circuit or feeder load.
• Comparing a load’s measured volts and amps with transformer, UPS, inverter, generator, or power-supply VA ratings.
• Estimating the VA contribution of a load before detailed demand, diversity, or power-factor information is available.
• Checking whether a measured current increase is associated with a corresponding increase in apparent loading.
• Developing an initial load schedule or equipment load inventory.
• Evaluating voltage-drop conditions by pairing measured load current with conductor length, conductor size, conductor material, and circuit voltage in a separate voltage-drop calculation.
• Reviewing power demand for equipment that is rated in VA rather than watts, including many transformers and electronic power systems.

The result can support a broader electrical calculation workflow, but it does not determine conductor size. Conductor selection requires ampacity, terminal rating, insulation temperature rating, ambient temperature correction factor, adjustment factor for current-carrying conductors, installation method, overcurrent protection, and applicable AHJ requirements.

To continue from apparent power to active power, compare the result with the AC Watts From Voltage And Current Calculator and enter a reviewed power-factor value.

Field and Code Limits

This calculation performs single-phase RMS apparent-power arithmetic only. It does not determine power factor, watts, reactive power, demand load, continuous-load treatment, conductor ampacity, AWG or kcmil conductor size, raceway fill, overcurrent-protective-device rating, equipment suitability, utility billing demand, or code compliance.

Use the correct system relationship for the equipment being reviewed. The worksheet is not a three-phase VA calculator and does not apply a phase multiplier. Three-phase apparent-power calculations require the appropriate line-to-line voltage and three-phase formula.

The calculated VA also does not establish that a circuit is adequately designed or installed. Final branch-circuit and feeder decisions require verification of actual load characteristics, nameplate instructions, voltage conditions, conductor terminations, equipment ratings, protection requirements, voltage drop, and applicable electrical-code requirements enforced by the AHJ.