Convert Volts to kW Calculator: Formula and Examples

This volts-to-kilowatts calculator estimates real electrical power from voltage, current, and—when needed—power factor. Enter volts and amps, choose single- or three-phase AC, and provide a power factor for AC; the result is kilowatts (kW).

Formula

For DC and single-phase AC, apparent power in volt-amperes is voltage multiplied by current. For three-phase AC using line-to-line voltage and a balanced load, apparent power is √3 multiplied by line-to-line voltage and line current. Real power in kilowatts is apparent power multiplied by power factor and divided by 1,000:

kW = V × A × phase factor × PF ÷ 1,000

• V is voltage in volts.
• A is current in amperes (amps).
• Phase factor is 1 for DC or single-phase AC, and √3 (about 1.732) for balanced three-phase AC when using line-to-line voltage and line current.
• PF is power factor, a unitless value from 0 to 1. For an ideal DC load, use 1; for AC, use the known power factor if real power is required.
• Divide watts by 1,000 to express the result in kilowatts. The calculator also reports apparent power in kVA, calculated without multiplying by power factor.

The calculator applies a power factor to every option. For DC, power factor is normally 1, so leave it at that default. The selectable three-phase formula assumes a balanced load and line-to-line voltage. If your three-phase voltage is specified differently, or the load is unbalanced, this simple calculation may not apply.

Worked Example

Using the defaults—120 V, 10 A, single-phase AC, and power factor 1:

1. Phase factor = 1.
2. Real power = 120 × 10 × 1 × 1 ÷ 1,000 = 1.200 kW.
3. Apparent power = 120 × 10 × 1 ÷ 1,000 = 1.200 kVA.

These figures describe electrical input under the formula’s assumptions. They do not necessarily equal a device’s useful mechanical or thermal output.

Why Volts Alone Cannot Give Kilowatts

Voltage measures electrical potential difference; it is not a measure of power by itself. Current—the rate of electrical charge flow—is also needed to calculate watts. For instance, 120 V could correspond to 120 W at 1 A or 1,200 W at 10 A, assuming unity power factor and single-phase or DC conditions.

For DC, the basic relationship is watts = volts × amps. For AC, voltage and current can be out of phase, so multiplying them gives apparent power rather than necessarily the real power consumed or delivered. Power factor accounts for that distinction in the simplified formula. In practical AC systems, power factor may depend on the load and operating conditions; check equipment documentation or a suitable measurement rather than assuming it is always 1.

Choosing the Right Inputs

• Voltage: Enter the voltage relevant to the calculation, not a different nominal or measured value. For three-phase calculations, confirm whether the stated voltage is line-to-line or line-to-neutral.
• Current: Use amperes. If a label gives milliamps, divide by 1,000 before entering the value; for example, 500 mA is 0.5 A.
• Supply type: Choose DC, single-phase AC, or three-phase AC. Do not choose three-phase just because a system has multiple conductors.
• Power factor: Enter a value between 0 and 1 when known. A stated 85% power factor is 0.85, not 85.

For a balanced three-phase supply, the common √3 formula uses line-to-line voltage and the current in a line conductor. If you have phase voltage instead, a different form of the relationship may be needed. Verify the data format before comparing a calculation with a nameplate rating.

How to Read kW, kVA, and Related Units

A kilowatt is 1,000 watts and represents real power: the rate at which energy is transferred or converted. A kilovolt-ampere (kVA) represents apparent power in an AC circuit. The relationship is kW = kVA × power factor. When power factor is 1, kW and kVA have the same numerical value; below 1, kW is lower.

Energy is different from power. A kilowatt-hour (kWh) measures energy used over time. A steady 1 kW load operating for 2 hours uses 2 kWh. A volts-to-kW calculation alone does not establish energy consumption unless you also know how long the load runs and whether its power changes.

Common Errors and Limits

• Using voltage alone: You also need current, and AC real-power calculations may need power factor.
• Mixing units: Enter volts and amps, not kilovolts and milliamps, unless you convert them first. One kilovolt is 1,000 volts; one amp is 1,000 milliamps.
• Ignoring phase: The three-phase factor changes the result. The single-phase formula cannot simply be used with three-phase values.
• Assuming unity power factor: A default of 1 is convenient when the factor is unknown, but it can overstate AC real power if the actual factor is lower.
• Confusing input and output power: A motor, power supply, or other conversion device may have losses. The electrical input calculation is not automatically its useful output rating.

This is a general arithmetic calculator, not a method for selecting conductors, protective devices, or equipment ratings. Electrical systems can involve conditions that the basic equations do not represent. Use manufacturer data and qualified electrical guidance for real installations; do not treat a calculated number as a safety rating.

Frequently Asked Questions

Can you convert volts directly to kW?
No. Voltage alone is insufficient. You need current, and for AC real power you may also need the power factor and the phase arrangement.

What is the formula for volts and amps to kW?
For DC or single-phase AC, kW = volts × amps × power factor ÷ 1,000. For balanced three-phase AC using line-to-line volts, multiply by √3 as well.

How many kW is 220 volts?
There is no single answer without current and, for AC real power, power factor. At 10 A and unity power factor, single-phase power is 220 × 10 ÷ 1,000 = 2.2 kW.

Is kW the same as kVA?
No. kW is real power, while kVA is apparent power. For AC, kW equals kVA multiplied by power factor; they match numerically only when the factor is 1.

Does the three-phase formula use phase or line voltage?
The √3 formula shown here uses line-to-line voltage and line current for a balanced load. Check how the voltage is specified before using it.

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in v | Voltage | V | 120 | 0 | 1000000
in i | Current | A | 10 | 0 | 1000000
sel ph | Supply type | Single-phase AC=1, Three-phase AC=1.7320508075688772, DC=1
in pf | Power factor | - | 1 | 0.000001 | 1
out kw | Real power | kW | v * i * ph * pf / 1000 | 3
out kva | Apparent power | kVA | v * i * ph / 1000 | 3