Determine the optimal inverter size for your power needs
Sum of all appliance power
Highest momentary load
Base Requirement: 0 W
With Safety Margin: 0 W
Efficiency Adjusted: 0 W
Recommended Inverter Size: 0 W
No appliances added yet. Start by adding appliances in the configuration panel.
Total Appliances: 0
Total Power: 0 W
An inverter is an electronic device that converts direct current (DC) to alternating current (AC). The converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits.
Inverters are commonly used in solar power systems, RVs, boats, and backup power solutions to power standard household appliances from batteries.
Continuous Power (Watts): This is the amount of power an appliance uses during normal operation. For example, a 60W light bulb uses 60 watts continuously when turned on.
Surge Power (Watts): Some appliances, particularly those with motors (like refrigerators or power tools), require a brief surge of power when starting up. This can be 3-7 times their normal operating power.
When sizing an inverter, you must account for both the continuous power requirements of all appliances that might run simultaneously, and the highest surge power that might occur.
The basic formula for inverter sizing is:
Inverter Size = (Total Load × Safety Margin) / Inverter Efficiency
Where:
The inverter must also be able to handle the highest surge power requirement among your appliances.
For DC systems (like solar or RV setups), you'll need to consider battery requirements:
DC Current (Amps) = Total Load (Watts) / Battery Voltage (Volts)
For example, a 500W load on a 12V system would draw about 41.7A (500W ÷ 12V).
To calculate battery capacity needed for a certain runtime:
Battery Capacity (Ah) = (Total Load (W) × Runtime (hours)) / Battery Voltage (V)
Remember to account for battery depth of discharge (typically 50% for lead-acid batteries) and inverter efficiency in real-world calculations.
This calculator determines the apparent power capacity (VA or Watts) required for an inverter to safely power your AC loads from a DC source. Proper inverter sizing is critical for:
This tool is used by professionals in multiple disciplines:
1. Base Inverter Requirement:
Ibase = max(∑Pcontinuous, Psurge_max)
Where:
∑Pcontinuous = Sum of all continuous power loads (W)
Psurge_max = Maximum surge power of any single appliance (W)
2. Efficiency-Adjusted Requirement:
Iadj = Ibase × (1 + Msafety/100) ÷ (η/100)
Where:
Msafety = Safety margin percentage (%)
η = Inverter efficiency percentage (%)
3. Battery Current Calculation:
IDC = Ptotal ÷ VDC
Where:
IDC = DC input current (A)
VDC = Battery bank voltage (V)
IMPORTANT: This tool provides theoretical calculations for educational and planning purposes only.
The calculator assumes:
Note: Real inverters have non-linear efficiency curves; these calculations use simplified constant efficiency.
For resistive loads (heaters, incandescent lights), Watts = VA. For reactive loads (motors, electronics), VA > Watts due to power factor. This calculator assumes unity PF for simplicity. In professional designs, use VA rating and consider PF derating.
Inverters typically derate above 40°C ambient. Add 10-20% margin for installations in hot environments or enclosures. Refer to manufacturer datasheets for specific temperature derating curves.
Continuous Rating: Power inverter can deliver indefinitely without overheating.
Surge Rating: Short-term overload capability (typically 3-5 seconds) for motor starting. Must be ≥ highest appliance surge requirement. For motor startup analysis, also check our motor starting current calculator.
Increase safety margin to 30-40% or add 20% to calculated size. Consider modular inverter systems for large anticipated growth. Document all assumptions for future reference.
Inverter sizing is one component of complete system design. Related calculations include:
Last reviewed for technical accuracy: September 2025. Based on NEC 2023 and IEEE 1547-2018 standards.