Three-Phase Power Calculator
Estimate kW, kVA, kVAR, and line current for balanced three-phase systems.
AEO summary
A three-phase power calculator estimates kVA, kW, kVAR, and line current for a balanced three-phase system.
Use this page when you need a quick answer about three-phase load demand from either current-based or power-based inputs. It helps show how line voltage, current, power factor, and efficiency combine into the key power values used in design and troubleshooting.
- Useful for balanced three-phase load checks and feeder planning.
- Shows the relationship between apparent, real, and reactive power.
- Helps estimate line current from known power conditions.
Three-Phase Inputs
Calculated Results
How to read the result: apparent power is the total three-phase demand, real power is the working portion, reactive power shows the non-working component, and estimated line current is the current implied by the selected operating assumptions.
If kVA or current appears high, review the entered power factor, efficiency, and whether the balanced-system assumption matches the actual installation.
⚠️ Engineering Caution:
This tool is intended for screening and pre-check workflows. Results are usually directionally useful, but they
can still shift with equipment selection, environmental conditions, naming conventions, revision status, or
interpretation rules. Confirm any value that affects ordering, substitution, compliance, or installation before
acting on it.
Frequently Asked Questions
What formula does a three-phase power calculator use?
For a balanced three-phase system, apparent power is calculated as √3 × line-to-line voltage × line current, and real power is that value multiplied by power factor.
Why does current rise when power factor drops?
For the same real power, a lower power factor means more apparent power is required, which increases line current and can affect feeders, transformers, and voltage drop.
What This Calculator Is For
Three-phase systems are common in industrial and commercial power distribution, motor loads, HVAC equipment, pumps, compressors, panels, and drives. In real work, users often need quick answers to questions like:
- How many kilowatts is this three-phase load drawing?
- What is the apparent power in kVA?
- How much reactive power is involved at the current power factor?
- If I know kW, what line current should I expect at this voltage?
- How much does poor power factor change current demand?
This calculator is designed for those practical checks.
Core Three-Phase Relationships
For balanced three-phase systems, the standard line-to-line power relationships are:
Apparent Power (VA) = √3 × V × AReal Power (W) = √3 × V × A × PFReactive Power (VAR) = √(VA² - W²)
Where:
Vis line-to-line voltageAis line currentPFis power factor
The calculator also works in reverse by estimating current when real power is known:
A = W ÷ (√3 × V × PF)
What Users Usually Need
In practice, most users are not doing a full power-quality study. They usually need a fast engineering estimate for:
- load planning
- feeder and panel checks
- equipment comparison
- current impact of low PF loads
- rough generator or transformer sizing discussions
- estimating whether measured current is reasonable for a known kW load
That is the scope of this tool.
Important Limitations
This calculator assumes a reasonably balanced three-phase system and steady-state operation. It is not intended to replace:
- detailed harmonic analysis
- unbalanced load studies
- transient or inrush calculations
- utility billing validation
- protection coordination studies
- final equipment nameplate verification
Real field conditions may differ when:
- voltage varies significantly under load
- the system is unbalanced
- variable-speed drives distort waveform shape
- PF changes with load or operating point
- measurements are taken during transient conditions
Practical Guidance
Use this tool when you need a quick answer that is directionally reliable for engineering work. For design signoff, commissioning, or troubleshooting, compare the result with real measurements or manufacturer data.
FAQ
What is the difference between kW and kVA?
kW is real power — the portion that performs actual work. kVA is apparent power — the total volt-ampere demand seen by the system. The relationship between them depends on power factor.
Why does low power factor increase current?
For the same real power, lower power factor means the system must carry more current to deliver that power. That can affect cable sizing, voltage drop, and upstream equipment loading.
Can I use this for motors and VFD loads?
Yes, as a practical estimate. But for final design or troubleshooting, always compare against measured data and manufacturer documentation.
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