Motors & Loads calculator
Three Phase Motor Calculator
A 25 HP, 480V, 0.86 PF, 91% efficient three-phase motor screens at about 28.66 A, 20.49 kW of electrical input, 23.83 kVA, and 12.16 kVAR. A measured 35 A at the same operating point estimates about 30.53 HP of shaft output. This page is a balanced three-phase motor operating-point screen. It converts motor output to estimated line current, or measured line current to estimated shaft output, using the entered voltage, power factor, and efficiency. The page is intentionally narrower than a NEC branch-circuit sizing workflow, an overload-setting page, or a starting-current study.
Updated July 10, 2026
A 25 HP, 480V, 0.86 PF, 91% efficient three-phase motor screens at about 28.66A with 20.49 kW of electrical input, 23.83 kVA, and 12.16 kVAR.
Balanced operating point: input kW = output kW ÷ η | line current = kVA × 1000 ÷ (√3 × V)
Choose whether you are starting from motor output or line current, then enter voltage, power factor, and efficiency to screen current, kW, kVA, kVAR, and estimated shaft output
Example Calculations
How to Use
How to use the three-phase motor calculator
- Select whether you want to estimate line current from motor output or motor output from line current.
- Enter the balanced three-phase line-to-line voltage. Common U.S. low-voltage checks are 208V, 230V, 460V, 480V, and 575V.
- Enter either the motor output in HP or kW, or the line current in amperes.
- Enter the operating power factor and efficiency.
- Review the line current, electrical input power, apparent power, reactive power, and estimated shaft output.
Core balanced three-phase relationships used here
Input kW = Output kW ÷ Efficiency
kVA = Input kW ÷ Power Factor
Line Current = kVA × 1000 ÷ (√3 × Line-to-Line Voltage)
Output kW = Input kW × Efficiency
What the page returns
| Output | Meaning | Why it matters |
|---|---|---|
| Line current | Balanced three-phase operating current | Useful for quick feeder, panel, and transformer loading checks |
| Electrical input power | Real electrical power flowing into the motor | Shows the difference between electrical input and shaft output |
| Apparent power | Total kVA at the operating point | Useful when reviewing upstream transformer and distribution loading |
| Reactive power | kVAR associated with the entered power factor | Helps explain why low power factor raises current for the same shaft output |
| Estimated shaft output | Mechanical output expressed in kW and HP | Useful when you start from measured current and want an operating-point estimate |
Important scope notes
- This page assumes a balanced three-phase operating point.
- It does not replace motor nameplate data, manufacturer data, or a commissioned test.
- It does not perform NEC table full-load current sizing, overload settings, branch-circuit protection sizing, or starting-current analysis.
- Use the Motor Current Calculator when the job is formula running-current comparison, the Full Load Current Calculator when the job is NEC table FLC lookup, and the Motor Starting Current Calculator when the real question is inrush.
Example: a 25 HP motor at 480V, 0.86 PF, and 91% efficiency screens at about 28.66 A, 20.49 kW of electrical input, 23.83 kVA, and 12.16 kVAR.
If you start instead with a measured 35 A at the same 480V, 0.86 PF, and 91% efficiency, the same operating point screens at about 25.02 kW of electrical input and about 30.53 HP of estimated shaft output.
Use the Motor Power Calculator for broader electrical/mechanical conversion paths, the Power Factor Correction Calculator when the real question is capacitor-kVAR screening, and the Transformer Calculator when you need the upstream transformer current and kVA view.
Common Applications
More applications. Open to review 2 additional use cases.
Frequently Asked Questions
What is the main formula behind this calculator?
For a balanced three-phase motor, the page first connects output power, efficiency, and input power, then uses power factor to move from input kW to kVA, and finally converts kVA to line current with I = kVA × 1000 ÷ (√3 × V).
Why is this page different from the Motor Current Calculator?
Because this page is an operating-point estimate. The Motor Current Calculator is the better page for formula running-current comparison, while the Full Load Current Calculator is the better page for NEC table full-load-current lookup and the starting-current page is for inrush screening.
Why is electrical input power higher than shaft output?
Because efficiency is never 100%. Input power must cover both the useful mechanical output and the motor losses, so the electrical input kW is always higher than the shaft-output kW when efficiency is below 100%.
Can I use measured current to estimate motor output?
Yes, as long as you also enter realistic voltage, power factor, and efficiency for that same operating point. The result is still an estimate, not a replacement for direct mechanical measurement or full manufacturer data.
Should I use this page for VFD setup or branch-circuit sizing?
No. A VFD application or a branch-circuit sizing task needs a different workflow. Use this page only for balanced three-phase operating-point estimates, then move to the dedicated motor-current, starting-current, or manufacturer-specific workflow as needed.
Related Calculators
Motor Current Calculator
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Motor Starting Current Calculator
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Motor Power
Open the motor power for related motors & loads review.
Power Factor Correction Calculator
Screen capacitor kvar, corrected kVA, and line-current reduction for balanced three-phase loads.
Transformer Calculator
Screen transformer kVA, turns ratio, full-load current, losses, and a basic impedance-based fault-current check.
Electrical Load Calculator
Estimate demand load and service ampacity using NEC-style demand and diversity factors.