When comparing diesel generators, you will often see power ratings expressed in both kW and kVA. For example, a generator may be rated at 100 kVA / 80 kW.
Although kW and kVA are closely related, they represent different electrical quantities. Understanding the difference helps you read generator specifications correctly and match generator ratings with electrical applications.
kW vs kVA: The Basic Difference
| Rating | Meaning | Unit |
|---|---|---|
| kW | Active power | Kilowatt |
| kVA | Apparent power | Kilovolt-ampere |
| PF | Power factor | Ratio |
kW represents the active power that performs useful work or is converted into heat, light, motion, and other forms of energy.
kVA represents the total apparent power in an AC electrical system and accounts for both active and reactive components.
What Is Power Factor?
Power factor (PF) describes the relationship between active power and apparent power in an AC system.
PF = kW ÷ kVA
A lower power factor means more apparent power is required for the same active power. Motors, transformers, UPS systems, and other electrical equipment can have different power factor characteristics.
How kW, kVA and Power Factor Are Related
kW = kVA × PF
kVA = kW ÷ PF
PF = kW ÷ kVA
These formulas show why the kW and kVA values of a generator are different when the power factor is below 1.0.
How to Convert kVA to kW
Use the following formula:
kW = kVA × PF
Example: A 250 kVA generator at a power factor of 0.8:
250 × 0.8 = 200 kW
How to Convert kW to kVA
Use the following formula:
kVA = kW ÷ PF
Example: A load requires 160 kW at a power factor of 0.8:
160 ÷ 0.8 = 200 kVA
Why Are Diesel Generators Rated in kVA?
Generator alternators must handle the electrical current flowing through their windings. Because current is related to apparent power, the alternator rating is commonly expressed in kVA.
This also allows generator ratings to be compared across applications with different power factors.
For this reason, generator specifications commonly show both kVA and kW.
What Does a 100 kVA / 80 kW Generator Mean?
A generator rated at 100 kVA / 80 kW has an apparent power rating of 100 kVA and an active power rating of 80 kW at a power factor of 0.8.
100 kVA × 0.8 = 80 kW
The two values describe different electrical characteristics and should not be added together.
What Happens When Power Factor Changes?
For the same active power, a lower power factor results in a higher kVA requirement.
| Load | Power Factor | Required kVA |
|---|---|---|
| 80 kW | 1.0 | 80 kVA |
| 80 kW | 0.9 | 88.9 kVA |
| 80 kW | 0.8 | 100 kVA |
| 80 kW | 0.7 | 114.3 kVA |
How to Read kW and kVA on a Generator Specification
A typical diesel generator specification may list:
○ Rated power: 500 kVA / 400 kW
○ Power factor: 0.8
○ Voltage: 400/230 V
○ Frequency: 50 Hz
○ Phase: Three-phase
The 500 kVA and 400 kW ratings describe the apparent and active power capabilities of the same generator at the specified power factor.
kW vs kVA: Quick Reference
| Item | Formula / Meaning |
|---|---|
| kW | Active power |
| kVA | Apparent power |
| Power Factor | PF = kW ÷ kVA |
| kVA to kW | kW = kVA × PF |
| kW to kVA | kVA = kW ÷ PF |
Related Article
Diesel Generator Sizing Guide: How to Calculate the Right Generator Capacity
Conclusion
kW measures active power, while kVA measures apparent power. The difference between them is determined by power factor.
For diesel generators, understanding kW, kVA, and power factor makes it easier to read technical specifications and evaluate electrical requirements accurately.
Contact GENLITEC POWER for diesel generator sets and professional power solutions.
Post time: Aug-17-2026
