Calculate inverter efficiency, input power, or output power from any two values, with watts, kilowatts, and megawatt units supported.
Customize This Calculator
Build your own version. Describe what you want changed, added, or compared.
Inverter Efficiency Formula
The basic inverter efficiency formula compares usable AC output power to DC input power:
The same relationship can be rearranged to solve for the missing value:
- η = inverter efficiency, as a percentage
- Pin = inverter input power, usually DC power supplied to the inverter
- Pout = inverter output power, usually AC power delivered by the inverter
The calculator lets you enter any two values and solves for the third. If you enter input power and output power, it calculates efficiency. If you enter input power and efficiency, it calculates output power. If you enter output power and efficiency, it calculates the required input power.
Power values can be entered in watts, kilowatts, or megawatts. The calculation converts the selected units internally so the input and output power can use different units.
Typical Inverter Efficiency Ranges
| Inverter type or use | Typical efficiency range | Notes |
|---|---|---|
| Small portable inverter | 80% to 90% | Efficiency can drop at very low loads or near maximum load. |
| Modified sine wave inverter | 85% to 92% | May be less suitable for sensitive electronics or inductive loads. |
| Pure sine wave inverter | 88% to 96% | Common for solar, battery backup, RV, and off-grid systems. |
| Grid-tie solar inverter | 94% to 98% | Often highest near its rated operating range. |
Power Unit Conversions
| Unit | Equivalent in watts | Example |
|---|---|---|
| 1 W | 1 W | 500 W = 500 W |
| 1 kW | 1,000 W | 2.5 kW = 2,500 W |
| 1 MW | 1,000,000 W | 0.01 MW = 10,000 W |
Example Calculations
Example 1: Calculate inverter efficiency
You measure 1,000 W going into an inverter and 920 W coming out.
The inverter efficiency is 92%.
Example 2: Calculate output power
An inverter receives 5 kW of input power and operates at 94% efficiency.
The inverter output power is 4.70 kW, or 4,700 W.
FAQ
Can inverter efficiency be over 100%?
No. A real inverter cannot output more power than it receives. If the calculated efficiency is over 100%, the most likely causes are mismatched units, measurement error, using input and output values from different times, or measuring apparent power instead of real power.
Why is output power lower than input power?
Some energy is lost inside the inverter as heat and in the switching electronics, transformer, wiring, cooling fan, and control circuits. Efficiency measures how much of the input power becomes useful output power.
Does inverter efficiency stay constant?
No. Efficiency changes with load, input voltage, temperature, and inverter design. Many inverters are most efficient at a moderate to high load, but less efficient at very light loads or when operating near their limits.
