Basic Electrical Laws calculator
Power Calculator
At 240V and 20A with 0.90 PF, this power calculator returns 4800 VA, 4320 W, and about 2092 VAR; the same page also solves balanced three-phase current, where 25 kW at 480V and 0.86 PF is about 34.97 A. It is a relationship screen for RMS power values, not a conductor, breaker, or NEC sizing workflow.
Updated July 16, 2026
A 120V DC load at 15A is 1800W. A 240V, 20A AC load at 0.90 PF is 4800 VA, 4320W, and about 2092 VAR.
DC: P = V × I | AC single-phase: S = V × I, then P = S × PF | AC three-phase: S = √3 × V × I
Choose DC, single-phase, or balanced three-phase below and enter a solvable set of voltage, current, power, or power-factor values
Example Calculations
More examples. Open to review 1 additional calculation example.
How to Use
How to use the power calculator
- Select DC, AC single phase, or AC three phase.
- Enter any solvable combination of values. The most common combinations are:
- Voltage + current for DC power or AC apparent power
- Voltage + current + power factor for full AC real and reactive power
- Real power + apparent power for AC power factor and reactive power
- Real power + reactive power for the AC power triangle
- Voltage + real power + power factor when you need current
- For balanced three-phase checks, enter line-to-line voltage and line current.
- Review the resolved values together instead of reading only one output in isolation.
Core formulas used here
DC: P = V × I
Single-phase AC apparent power: S = V × I
Balanced three-phase apparent power: S = √3 × V × I
Real power: P = S × PF
Reactive power magnitude: Q = √(S² − P²)
Power factor: PF = P ÷ S
What this page is good for
| Use case | What the page returns | What it does not replace |
|---|---|---|
| DC watts from volts and amps | Voltage, current, power, and equivalent resistance | Battery-runtime, converter-efficiency, or thermal design work |
| Single-phase AC load check | Real power, apparent power, reactive power, and power factor | Branch-circuit sizing, harmonic review, or waveform analysis |
| Balanced three-phase screen | Line current, line voltage, VA, W, VAR, and phase voltage | Unbalance studies, motor starting, or full distribution modeling |
Scope notes that matter
- AC outputs assume sinusoidal RMS values.
- Three-phase outputs assume a balanced load.
- The page shows reactive-power magnitude. It does not classify leading versus lagging from distortion or harmonic content.
- This page does not calculate conductor size, breaker size, motor branch-circuit sizing, transformer losses, or converter efficiency.
Example 1: a 120 V DC load at 15 A resolves to 1800 W and about 8.00 ohms.
Example 2: a 240 V, 20 A single-phase AC load at 0.90 PF resolves to about 4800 VA, 4320 W, and about 2092 VAR.
Example 3: a 25,000 W balanced three-phase load at 480 V and 0.86 PF resolves to about 29,070 VA and about 34.97 A of line current.
Use the Ohm's Law Calculator when the real question is V, I, and R rather than AC power. Use the Power Factor Correction Calculator when the real question is capacitor kVAR sizing. Use the Transformer Calculator when kVA, voltage, phase, impedance, or secondary current must stay with a transformer result. Use the Electrical Load Calculator when the power relationship becomes service demand, connected load, or panel planning. Use the Three Phase Motor Calculator when you are screening a motor operating point rather than a general electrical load.
Common Applications
More applications. Open to review 2 additional use cases.
Frequently Asked Questions
What is the difference between real power and apparent power?
Real power is the useful electrical power measured in watts. Apparent power is the total VA carried by the source and conductors. They are equal only when power factor is 1.0.
Why does AC need power factor while DC does not?
Because DC voltage and current do not have a phase-angle relationship. AC loads can shift current relative to voltage, so the same voltage and current can produce different real power depending on power factor.
Can I use this page for balanced three-phase current?
Yes, but only as a balanced three-phase screen using line-to-line voltage and line current. It is not an unbalance study or a harmonic analysis page.
What happens if I enter only voltage and current for AC?
The page can still return apparent power. Add power factor, or enter a real-and-apparent or real-and-reactive power pair, when you need watts and VAR.
Should I use this page for breaker or wire sizing?
No. Use this page to understand power relationships first, then move to breaker, wire, service-load, or motor-specific calculators for design decisions.
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