Engineering calculators

kVA Calculator

Updated Sep 1, 2026 By Jehan Wadia
Rate Formulas
Voltage, Current & kVA
Phase
V
The RMS voltage supplied to the circuit, in volts.
A
The current flowing through the circuit, in amperes.
kVA
Apparent power. Leave one of the three fields blank to solve for it.

Result

Step-by-Step Solution

Visualization

Introduction

This kVA calculator helps you find apparent power in an electrical circuit. kVA stands for kilovolt-amperes, and it measures the total power a device or system draws. Unlike kilowatts (kW), which only count the real power that does useful work, kVA includes both real power and reactive power. Knowing your kVA rating is important when you size generators, transformers, wiring, and other electrical equipment.

The calculator has two modes. In the first mode, you enter voltage and current to calculate kVA, or leave any one of the three fields blank to solve for it. This mode works for both single-phase and three-phase systems. In the second mode, you use kW and power factor to find kVA, or solve for any missing value in that group. Each calculation gives you a step-by-step solution and a chart so you can see how the values relate to each other.

How to Use Our kVA Calculator

Enter any two known values in a tab and leave the third field blank. The calculator will solve for the missing value and show the answer, a step-by-step solution, and a chart.

Voltage, Current & kVA Mode

Phase: Pick either Single-Phase or Three-Phase. This tells the calculator which formula to use. Three-phase systems multiply by 1.7321 (√3).

Voltage (V): Enter the RMS voltage of your circuit in volts. This is the electrical pressure that pushes current through the system.

Current (A): Enter the current flowing through the circuit in amps. This is how much electricity the load draws.

kVA: Enter the apparent power in kilovolt-amperes. Leave this field blank if you want the calculator to find it from the voltage and current you entered.

kW, Power Factor & kVA Mode

Real Power (kW): Enter the active power your load uses in kilowatts. This is the actual work the electricity does.

Power Factor (PF): Enter a number between 0.01 and 1.00. Power factor shows how much of the apparent power is doing real work. A value of 1.00 means all power is used. A lower number means some power is wasted.

Apparent Power (kVA): Enter the total apparent power in kilovolt-amperes. Leave this field blank if you want the calculator to find it from the kW and power factor you entered.

What Is kVA?

kVA stands for kilovolt-ampere. It is a unit that measures apparent power in an electrical circuit. Apparent power is the total power that flows through wires to a device or load. It includes both the power that does useful work and the power that is lost or wasted along the way.

How kVA Is Calculated

There are two main ways to find kVA. The first uses voltage and current. For a single-phase circuit, you multiply volts by amps and divide by 1,000. For a three-phase circuit, you also multiply by 1.7321 (the square root of 3) before dividing by 1,000. The second way uses real power (kW) and power factor. You divide kW by the power factor to get kVA. These relationships are rooted in the same principles behind Ohm's Law, which connects voltage, current, and resistance in any circuit.

Single-Phase Formula

kVA = (Volts × Amps) ÷ 1,000

Three-Phase Formula

kVA = (Volts × Amps × 1.7321) ÷ 1,000

Power Factor Formula

kVA = kW ÷ Power Factor

kVA vs. kW

kW (kilowatts) measures real power: the energy that actually does work, like spinning a motor or lighting a bulb. kVA measures apparent power, the full amount of power drawn from the source. The difference between them is caused by reactive power, which moves back and forth in the circuit without doing useful work. Reactive power is closely related to impedance in the circuit. The power factor tells you how much of the apparent power is real power. A power factor of 1.0 means all the power is doing useful work, so kVA equals kW. A lower power factor means more power is wasted.

Why kVA Matters

Generators, transformers, and UPS systems are all rated in kVA. Their wiring and components must handle the full apparent power, not just the real power. If you only look at kW and ignore kVA, you could overload your equipment. Knowing the correct kVA helps you pick the right size generator or transformer for your needs and keeps your electrical system safe and efficient.

Formulas used

Single-Phase Apparent Power (kVA)
\text{kVA} = \frac{V \times I}{1000}
Three-Phase Apparent Power (kVA)
\text{kVA} = \frac{V \times I \times \sqrt{3}}{1000}
Apparent Power from Real Power and Power Factor
\text{kVA} = \frac{\text{kW}}{\text{PF}}
Real Power from Apparent Power and Power Factor
\text{kW} = \text{kVA} \times \text{PF}
Power Factor from Real and Apparent Power
\text{PF} = \frac{\text{kW}}{\text{kVA}}
Reactive Power (kVAR)
\text{kVAR} = \sqrt{\text{kVA}^2 - \text{kW}^2}

Frequently asked questions

What does kVA stand for?

kVA stands for kilovolt-ampere. It is a unit of apparent power in an electrical system. One kVA equals 1,000 volt-amperes. It tells you the total power flowing through a circuit, including both real power and reactive power.

What happens if I fill in all three fields?

The calculator will show an error message. It needs exactly one blank field so it knows which value to solve for. Clear one of the three fields and try again.

When should I use single-phase vs. three-phase?

Use single-phase for most homes and small loads that run on two wires (hot and neutral). Use three-phase for commercial or industrial systems that use three hot wires. Three-phase power is common in factories, large motors, and big HVAC units. If you are not sure, check the nameplate on your equipment or your electrical panel.

Why does the three-phase formula multiply by 1.7321?

The number 1.7321 is the square root of 3 (√3). In a three-phase system, three separate voltage waves are spaced 120° apart. Multiplying by √3 accounts for how these three waves combine to deliver more total power than a single phase at the same voltage and current.

What is power factor?

Power factor is a number between 0 and 1 that shows how much of the apparent power is doing real work. A power factor of 1.0 means all the power is useful. A power factor of 0.8 means only 80% of the apparent power does real work. The rest is reactive power that flows back and forth without doing useful work.

What is a typical power factor for common loads?

Resistive loads like heaters and incandescent lights have a power factor close to 1.0. Motors usually range from 0.75 to 0.90. Fluorescent lighting is around 0.85 to 0.95. Computers and electronics often fall between 0.60 and 0.95 depending on whether they have power factor correction.

Can kVA ever equal kW?

Yes. When the power factor is exactly 1.0, kVA equals kW. This means all the apparent power is real power and nothing is wasted as reactive power. Purely resistive loads like electric heaters come close to this.

Why is my kVA higher than my kW?

kVA is always equal to or greater than kW. The difference comes from reactive power. Reactive power does not do useful work, but it still flows through the wires. A lower power factor means a bigger gap between kVA and kW.

What voltage value should I enter?

Enter the RMS voltage of your circuit. For most U.S. homes this is 120 V or 240 V. For commercial three-phase systems, common values are 208 V, 277 V, or 480 V. Check your panel or equipment nameplate for the exact number.

How do I size a generator using kVA?

Add up the kVA of all the loads you plan to run at the same time. Then pick a generator rated at or above that total. It is smart to add a 20–25% safety margin to handle startup surges from motors and other inductive loads.

How do I convert kVA to amps?

For single-phase: Amps = (kVA × 1,000) ÷ Volts. For three-phase: Amps = (kVA × 1,000) ÷ (Volts × 1.7321). You can use this calculator to do it. Enter the kVA and voltage, leave the current field blank, and press Calculate.

How do I convert amps to kVA?

For single-phase: kVA = (Volts × Amps) ÷ 1,000. For three-phase: kVA = (Volts × Amps × 1.7321) ÷ 1,000. Enter the voltage and current in this calculator, leave the kVA field blank, and press Calculate.

What is reactive power (kVAR)?

kVAR stands for kilovolt-ampere reactive. It is the part of apparent power that does not do useful work. It flows back and forth between the source and loads like motors and transformers. The power triangle links all three: kVA² = kW² + kVAR². The chart in Tab 2 of this calculator shows all three values side by side.

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