When to use this calculator
Find reactive-power magnitude from compatible apparent and real power. Sinusoidal power-triangle magnitude only; leading/lagging sign and distortion power are not inferred.
Explore the ac power & reactance calculators for other questions in this topic. For a related calculation, use the RL Filter Cutoff Calculator: Find the characteristic cutoff frequency of a simple RL filter.
PUTTING IT INTO PRACTICE
Reactive Power: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Apparent power (VA) | 1,000 |
| Real power (W) | 800 |
| Result | 600 var |
- Check the input labels and enter the example values above.
- Apply the relationship: Reactive power magnitude = √(apparent²−real²).
- The result is 600 var, rounded for display.
How to interpret your result
Sinusoidal power-triangle magnitude only; leading/lagging sign and distortion power are not inferred.
Use RMS values in the AC power relationships. Apparent power is measured in VA and real power in watts. Pure-sine conversions and balanced three-phase equations only apply under their stated assumptions.
Frequently asked questions
Why can volt-amps differ from watts?
Apparent power is the RMS voltage-current product, while real power also reflects power factor. They are numerically equal only at a power factor of one.
When is the reactive power calculator useful?
Find reactive-power magnitude from compatible apparent and real power. Sinusoidal power-triangle magnitude only; leading/lagging sign and distortion power are not inferred.
How do I use the reactive power calculator?
Enter apparent power (va), real power (w). The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Reactive power magnitude = √(apparent²−real²).
What should I check before using the result?
Sinusoidal power-triangle magnitude only; leading/lagging sign and distortion power are not inferred.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
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