Power conversion equations
These equations convert real power, apparent power, and current for DC, single-phase AC, and balanced three-phase AC systems.
I = P / (V × η)I = P / (V × PF × η)I = P / (√3 × V × PF × η)S = P / PFwhere:
- I
- Calculated currentA
- P
- Real power converted to wattsW
- V
- System voltageV
- PF
- Power factor for AC systems
- η
- Efficiency as a decimal
- S
- Apparent powerkVA
Use equipment nameplate current when available, especially for nonlinear loads, motor loads, or equipment with high starting current.
Assumptions
- Balanced three-phase load
- Power factor applies to AC systems only
- Efficiency is treated as input-side correction
Important Warnings
- Use nameplate data when available.
- Nonlinear loads, harmonics, and starting current are not included.
FAQ
What is the difference between kW and kVA?
kW is real power. kVA is apparent power. For AC systems, kW = kVA x power factor.
Can I use this for motors?
Yes for a first estimate, but the motor current calculator is better because it includes efficiency and overload context.