Physics calculators

kW Calculator

Updated Jul 18, 2026 By Jehan Wadia
Rate Formulas

1 · kW from Volts, Amperes & Power Factor

Power System Phase
Single-phase is common in homes; three-phase is common in industrial settings.
Power Factor (PF)
Power (kW)
72.96 kW
= 72,960 W
Step-by-Step Solution
Power Triangle Components

2 · kW ↔ kVA Converter

2A · kW to kVA
Power Factor (PF)
Apparent Power (kVA)
600 kVA
2B · kVA to kW
Power Factor (PF)
Real Power (kW)
480 kW

3 · kW ↔ HP Converter

3A · kW to HP
Horsepower (HP)
67.05 HP
3B · HP to kW
Power (kW)
49.96 kW

Introduction

This kW calculator helps you find how much power a device or system uses. You can enter volts, amps, and power factor to get a result in kilowatts (kW) and watts. It works for both single-phase and three-phase power systems.

The calculator also lets you convert between kW and kVA (kilovolt-amps) and between kW and HP (horsepower). Each calculation shows the formula used and a step-by-step solution so you can follow the math yourself.

Use it to size generators, check motor ratings, plan electrical loads, or solve homework problems. Just type in your numbers, and the tool gives you an answer right away.

How to Use Our kW Calculator

Enter your electrical values below to calculate power in kilowatts (kW), convert between kW and kVA, or convert between kW and horsepower (HP). The calculator gives you instant results, a step-by-step solution, and a power triangle chart.

Section 1: Calculate kW from Volts, Amps & Power Factor

Pick your phase type. Choose 1-Phase if you have a standard home or small business setup. Choose 3-Phase if you have an industrial or commercial power system.

Enter the voltage in volts. Type the voltage of your circuit into the Voltage field. This is measured in volts (V).

Enter the current in amperes. Type the current flowing through your circuit into the Current field. This is measured in amps (A). If you need to find current from other values, try our Amp Calculator.

Set the power factor. Click 0.8 for a typical motor load, 1.0 for a purely resistive load like a heater, or click Custom and type any value between 0.01 and 1.00. You can also use our dedicated PF Calculator to determine your power factor.

Click Calculate to see your result in kW and watts, a full step-by-step solution, and a bar chart showing real, reactive, and apparent power.

Section 2: Convert Between kW and kVA

To convert kW to kVA, type your real power in kilowatts into the kW field on the left. Then pick or enter a power factor. The tool shows the apparent power in kVA. For more detailed kVA calculations, see our kVA Calculator.

To convert kVA to kW, type your apparent power in kilovolt-amperes into the kVA field on the right. Then pick or enter a power factor. The tool shows the real power in kW.

Section 3: Convert Between kW and HP

To convert kW to HP, type your power in kilowatts into the kW field on the left. The tool shows the equal value in mechanical horsepower. For more detailed conversions, see our Horsepower Calculator.

To convert HP to kW, type your horsepower into the HP field on the right. The tool shows the equal value in kilowatts.

All sections update in real time as you type. You can also press Enter on your keyboard or click the Reset button in any section to restore the default values.

What Is a Kilowatt (kW)?

A kilowatt (kW) is a unit that measures real power — the actual energy a device uses or produces every second. One kilowatt equals 1,000 watts. When you turn on a light, a motor, or an air conditioner, the power it draws is often measured in kilowatts.

How This kW Calculator Works

This calculator helps you find power in kilowatts using values you already know. In Section 1, you enter voltage (volts), current (amperes), and power factor to get kW. You can choose between a 1-phase system, which is common in homes, or a 3-phase system, which is used in factories and large buildings.

The formula for a 1-phase system is:

kW = (V × I × PF) ÷ 1,000

The formula for a 3-phase system is:

kW = (√3 × V × I × PF) ÷ 1,000

These formulas are based on Ohm's Law and standard AC power relationships. If you need to work backwards and find amps from kilowatts, use our kW to Amps Calculator.

What Is Power Factor?

Power factor (PF) is a number between 0 and 1. It tells you how much of the electricity flowing through a circuit does useful work. A power factor of 1.0 means all the power is used. A lower number, like 0.8, means some power is wasted. Motors, pumps, and compressors often have a power factor below 1.

kW vs. kVA

kW is real power — the power that does actual work. kVA (kilovolt-amperes) is apparent power — the total power supplied to a circuit. The difference between them is caused by the power factor. The formula is simple:

kVA = kW ÷ PF

Generators and transformers are often rated in kVA, so converting between kW and kVA is useful when sizing equipment. You can also convert between kVA and amps or between amps and watts using our other tools.

kW vs. Horsepower (HP)

Horsepower is an older unit of power still used for engines and motors. One horsepower equals about 0.7457 kW. To convert kW to HP, multiply by 1.341. To convert HP to kW, multiply by 0.7457. This is helpful when comparing electric motors to gas or diesel engines, or when calculating a vehicle's power-to-weight ratio. To estimate how much your electrical usage costs, check out our Electricity Cost Calculator. If you're planning a renewable energy system, our Solar Panel Calculator can help you determine how many panels you need based on your power requirements in kW.

Formulas used

kW from Volts, Amps & PF (1-Phase)
kW = \frac{V \times I \times PF}{1000}
kW from Volts, Amps & PF (3-Phase)
kW = \frac{\sqrt{3} \times V \times I \times PF}{1000}
kW to kVA
kVA = \frac{kW}{PF}
kVA to kW
kW = kVA \times PF
Reactive Power (Power Triangle)
kVAR = \sqrt{kVA^2 - kW^2}
kW to Horsepower
HP = kW \times 1.341
Horsepower to kW
kW = HP \times 0.7457

Frequently asked questions

What is the difference between kW and kWh?

kW measures how much power a device uses at any moment. kWh (kilowatt-hour) measures how much energy it uses over time. For example, a 2 kW heater running for 3 hours uses 6 kWh of energy. Think of kW as speed and kWh as distance.

When should I choose 1-phase vs 3-phase in the calculator?

Choose 1-phase if you are working with a standard home outlet or small business circuit. Choose 3-phase if you are working with industrial equipment, large motors, or commercial building power. If you are not sure, check the nameplate on your equipment or ask your electrician.

Why does the 3-phase formula use √3 (1.7321)?

A 3-phase system has three voltage waves that are offset from each other by 120 degrees. The √3 factor accounts for the way these three phases combine to deliver power. It comes from the geometry of the phase angles. Without it, the result would be wrong.

What power factor should I use if I don't know mine?

Use 0.8 as a safe general estimate. Most motors, pumps, and mixed loads run near this value. Use 1.0 only for purely resistive loads like heaters, incandescent lights, or electric kettles. If you need an exact number, check your equipment nameplate or use a power meter.

Can I enter decimal values for voltage and current?

Yes. All input fields accept decimal numbers. For example, you can enter 230.5 volts or 15.75 amps. The calculator handles fractional values and gives you a precise result.

What is reactive power (kVAR) shown in the chart?

Reactive power (kVAR) is the part of electricity that flows back and forth without doing useful work. It is needed by motors and transformers to create magnetic fields. The chart shows how total apparent power (kVA) splits into real power (kW) and reactive power (kVAR).

Is the HP conversion in this tool for mechanical or electrical horsepower?

This tool uses mechanical horsepower, which is the most common type. One mechanical HP equals 0.7457 kW. Electrical horsepower (0.746 kW) is very close but slightly different. For most practical uses, the difference is too small to matter.

Why is my kVA higher than my kW?

kVA is always equal to or higher than kW. This happens because kVA includes both useful power and wasted reactive power. The lower your power factor, the bigger the gap. At a power factor of 1.0, kW and kVA are equal.

Does this calculator work for DC circuits?

You can use it for DC by setting the power factor to 1.0 and choosing 1-phase. DC circuits have no reactive power, so the formula simplifies to kW = (V × I) ÷ 1,000. The result will be correct for any DC system.

How do I find amps if I only know kW and voltage?

Rearrange the formula: Amps = (kW × 1,000) ÷ (V × PF) for single-phase, or Amps = (kW × 1,000) ÷ (√3 × V × PF) for three-phase. You can also use our dedicated kW to Amps calculator for this.

What does the voltage value represent in a 3-phase system?

In a 3-phase system, the voltage you enter should be the line-to-line voltage, not the line-to-neutral voltage. Common values are 380V, 400V, 415V, 440V, or 480V. The √3 in the formula already accounts for the relationship between line and phase voltages.

Can I use this calculator to size a generator?

Yes. Add up the kW ratings of all loads you plan to run. Then use Section 2A to convert that total kW to kVA, since generators are often rated in kVA. Choose a generator rated at least 20% above your calculated kVA to handle startup surges.

Why does the calculator update as I type?

The calculator runs in real time to save you time. Every time you change a number or select an option, it recalculates instantly. You do not need to click the Calculate button each time, but you can if you prefer.

What happens if I enter zero or a negative number?

The calculator will show an error message in red below the input field. All values for voltage, current, kW, kVA, and HP must be positive numbers greater than zero. Power factor must be between 0.01 and 1.00.

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