RV & Off-Grid Inverter Sizing Calculator
In short, Determine the continuous and surge wattage rating your inverter must support, plus calculate the heavy DC battery cables and Class-T fuse required to feed it safely.
1. Simultaneous 120V AC Household Loads
Check the appliances you intend to power simultaneously through your inverter.
2. Battery Bank Voltage & Safety Margin
Continuous vs Surge Wattage for Common RV & Marine Appliances
| Appliance | Running Power (Watts) | Surge Multiplier | Peak Surge (Watts) | Recommended Inverter |
|---|---|---|---|---|
| RV Rooftop Air Conditioner (13.5k BTU) | 1,500W – 1,800W | 3.0x | 3,500W – 4,500W | 3,000W Pure Sine Wave (with Soft Start) |
| Microwave Oven (700W Cooking) | 1,050W – 1,150W | 1.5x | 1,600W | 2,000W Pure Sine Wave |
| Single Burner Induction Cooktop | 1,200W – 1,800W | 1.1x | 1,900W | 2,000W – 3,000W Pure Sine Wave |
| Residential 120V Refrigerator | 120W – 180W | 4.0x | 600W – 800W | 1,000W Pure Sine Wave |
Inverter Continuous Rating vs Motor Surge Capacity
When sizing an off-grid or mobile solar power inverter, you must account for both continuous running wattage and transient startup surge. Inductive loads like compressor refrigerators, air conditioners, and power tools draw 2x to 5x their nominal power for the first 500 milliseconds of operation. Always select an inverter with a continuous rating at least 20% to 25% higher than your maximum simultaneous continuous load to prevent thermal tripping during peak ambient temperatures.
Planning an RV or cabin installation? Check out our complete guide on What Size Inverter Do You Need for an RV or compare system architectures in 12V vs 24V Solar System Comparisons.
Frequently Asked Questions
How accurate are these engineering numbers?
All figures are derived directly from published empirical engineering standards including NEC 310.15, NREL photovoltaic datasets, and manufacturer polymer technical datasheets.
Are calculations processed on a remote server?
No. Every tool runs 100% locally in your client web browser with zero server transmission, guaranteeing complete data privacy.