Convert between watts, amps, volts and kVA for DC, single-phase and three-phase systems, using the power factor to relate real power (W) and apparent power (kVA).
Results are estimates for planning and education, based on your inputs and standard engineering values (AWG resistance, NEC ampacity, resistivity). Electrical work can be dangerous and is governed by the NEC and your local code — verify all sizing with a licensed electrician and your authority having jurisdiction (AHJ). Not a substitute for professional design.
Calculator
Real power
4,800 W
Real power
4.80 kW
Apparent power
4.80 kVA
Formula
Power from voltage and current depends on the system. DC: W = V × A (no power factor). AC single-phase: W = V × A × PF. AC three-phase: W = 1.732 × V × A × PF, where 1.732 is the square root of 3 and V is the line-to-line voltage. Apparent power is kVA = V × A / 1000 for DC and single-phase, and kVA = 1.732 × V × A / 1000 for three-phase. Real power (watts, what the load consumes) equals apparent power (volt-amps, what the source must supply) only when the power factor is 1; with PF below 1, W = VA × PF.
Worked example
240 V at 20 A on a DC circuit: W = 240 × 20 = 4,800 W = 4.80 kW, and kVA = 4,800 / 1,000 = 4.80 kVA (PF is 1 for DC). The same 240 V and 20 A on a single-phase AC circuit at 0.8 power factor delivers W = 240 × 20 × 0.8 = 3,840 W of real power while still drawing 4.80 kVA of apparent power. On a 208 V three-phase circuit at 20 A and PF 1: W = 1.732 × 208 × 20 = 7,205 W.
Frequently asked questions
How do I convert watts to amps?
Rearrange the power formula. DC or PF 1: A = W / V. Single-phase AC: A = W / (V × PF). Three-phase AC: A = W / (1.732 × V × PF). For example, 4,800 W on a 240 V DC or unity-PF circuit is 4,800 / 240 = 20 A.
What is the difference between watts (W) and kVA?
Watts is real power — the power actually converted into work or heat. kVA (kilovolt-amps) is apparent power — the product of voltage and current the source must supply. They are linked by the power factor: W = kVA × 1,000 × PF. With a PF of 1 they are equal; with a lower PF the source carries more current than the real power alone suggests, which is why generators and transformers are rated in kVA.
What is power factor?
Power factor is the ratio of real power (W) to apparent power (VA), between 0 and 1. Resistive loads such as heaters and incandescent lamps are near 1; motors and many electronic loads are lower because current and voltage fall out of phase. Use 1 for DC and purely resistive AC loads, and the nameplate or measured value otherwise.
Why is there a 1.732 factor for three-phase?
1.732 is the square root of 3. In a balanced three-phase system the line-to-line voltage and the per-phase contributions combine so that total power is P = √3 × V × I × PF. The factor lets you work from the easily measured line voltage and line current instead of phase quantities.
How do I convert kVA to amps?
Single-phase: A = kVA × 1,000 / V. Three-phase: A = kVA × 1,000 / (1.732 × V), using the line-to-line voltage. For instance a 10 kVA single-phase load at 240 V draws 10,000 / 240 = 41.7 A.
Does DC have a power factor?
No. Power factor describes the phase relationship between alternating voltage and current, so it applies only to AC. For DC, power is simply W = V × A and apparent power equals real power. Select the DC system here to ignore the power-factor field.
Source: P = V × I × PF (× √3 for three-phase); kVA = V × A / 1000 · All sources