Inverter Sizing Calculator
Size your power inverter correctly for solar, RV, and off-grid systems. Enter your load watts and surge factor to find the right inverter capacity.
Formula & How It Works
Inverter Size = Continuous Load / Efficiency Surge Capacity = Load × Surge Factor
Divide your total continuous load by the inverter efficiency to account for conversion losses. Most inverters are 85-95% efficient. The surge factor (typically 2x for inductive loads like motors) determines the peak power the inverter must handle for a few seconds during motor startup.
Inverter Sizing Reference Table
| Application | Continuous Load | Surge Load | Recommended Inverter |
|---|---|---|---|
| Small RV / Van | 500W | 1,000W | 1,000W |
| Large RV / Cabin | 1,500W | 3,000W | 2,000W |
| Off-Grid Cabin | 2,500W | 5,000W | 3,500W |
| Small Home Backup | 3,000W | 6,000W | 4,000W |
| Whole Home Off-Grid | 5,000W | 10,000W | 6,000W |
| Workshop / Job Site | 4,000W | 8,000W | 5,000W |
Choosing the Right Inverter
- Pure sine wave: Required for sensitive electronics, motors, and medical equipment
- Modified sine wave: Cheaper but can damage some electronics and cause motor buzzing
- Surge capacity: Most quality inverters handle 2x their rated output for 5+ seconds
- System voltage: Higher voltage (48V) means lower DC current, smaller wires, and less loss
- Idle consumption: Inverters draw 10-50W even with no load - factor this into battery sizing
Frequently Asked Questions
What size inverter do I need for my RV?
Most RVs need a 2,000-3,000W inverter to run a microwave, TV, lights, and small appliances. If you want to run an air conditioner, you will need at least 3,000-4,000W with a surge capacity of 6,000W+. A pure sine wave inverter is recommended for all RV electronics.
How do I calculate inverter size for solar?
Add up the wattage of all appliances you want to run simultaneously. Divide by the inverter efficiency (typically 90%). Then multiply by your surge factor (2x for motor loads). Round up to the nearest standard size (1,000W, 2,000W, 3,000W, etc.).
What is inverter surge capacity?
Surge capacity is the maximum power an inverter can deliver for a short period (usually 5-30 seconds) to start motors and compressors. Inductive loads like refrigerators, AC units, and pumps need 2-3x their running wattage during startup. Choose an inverter whose surge rating exceeds your highest starting load.
Pure sine wave vs modified sine wave - which do I need?
Pure sine wave inverters produce clean power identical to grid electricity, making them safe for all electronics, medical devices, and variable-speed motors. Modified sine wave inverters are cheaper but can cause buzzing in motors, reduce efficiency, and damage sensitive electronics. Always choose pure sine wave for whole-home or RV use.
What voltage should my inverter system be?
12V systems are fine for small loads under 1,500W. For 1,500-4,000W, use a 24V system to keep wire sizes manageable. For systems above 4,000W, 48V is recommended to minimize DC current, reduce wire costs, and improve efficiency.