What Size Power Inverter Do I Need?
Choose inverter wattage from simultaneous running loads, startup surge, battery voltage and practical operating margin.
The right inverter is large enough to start the load but not so oversized that idle consumption and cost become unnecessary.
This guide separates AC load sizing from battery, cable and runtime requirements.
Add Running Loads, Largest Surge and 20% Margin
Use 300W for electronics, 1,000W for small appliances, 2,000W for RV kitchen loads and 3,000W+ for air conditioners or large systems—after verifying surge.
Sizing Verdict
Choose pure sine wave and size the DC side as carefully as the AC side. Above 2,000W, 24V or 48V is often preferable.
Inverter Sizing Formula
Common Inverter Sizes
| Inverter Size | Typical Loads | 12V Full-Load Current |
|---|---|---|
| 300W | Laptop, camera, TV | About 28–30A |
| 1000W | Small tools, fridge, coffee maker | About 90–100A |
| 2000W | Microwave, RV kitchen, larger tools | About 185–200A |
| 3000W | Air conditioner, large RV, off-grid loads | About 275–300A |
Running vs Surge Power
Motors, compressors and some power supplies draw more power for a brief startup period. The inverter’s surge rating and duration must exceed that startup event.
12V vs 24V vs 48V
12V
Common in cars and small RVs, but current becomes extreme above 2kW.
24V
Cuts current roughly in half versus 12V.
48V
Best for larger off-grid systems.
Match the Battery Bank
Input voltage must match exactly.
Check BMS Limits
Lithium batteries can shut down on overcurrent.
Account for Cable Drop
Low DC voltage makes resistance critical.
Battery Runtime
Inverter wattage determines power capability, not runtime. Runtime depends on battery watt-hours, usable depth of discharge and inverter efficiency.
Sizing Examples
| Load | Running | Startup / Surge | Recommended Class |
|---|---|---|---|
| Laptop + TV | 180W | Low | 300–500W |
| Refrigerator | 150–800W | 1,000–2,200W | 1,500–2,000W |
| Microwave | 1,200–1,500W | Low/moderate | 2,000W |
| Small room AC | 700–1,500W | 1,800–3,500W | 2,000–3,000W |
| RV air conditioner | 1,200–1,800W | 2,500–5,000W | 3,000W+ with soft start |
Final Buying Checklist
Measure Actual Loads
Use nameplates or a watt meter.
Add Only Simultaneous Loads
Do not total everything owned.
Include the Largest Surge
Not every surge unless they overlap.
Choose Pure Sine Wave
Best general-purpose option.
Size the DC System
Battery, cables and fuse must support full load.
Add Margin
Avoid continuous operation at the ceiling.
Frequently Asked Questions
What size inverter runs a refrigerator?
Usually 1,500–2,000W with adequate surge.
What size runs a microwave?
Commonly 2,000W.
Can 1000W run an air conditioner?
Usually not most household or RV units.
Why is 24V better for large inverters?
It reduces current and cable size.
How much margin should I add?
About 20% is practical.
Does a bigger inverter give longer runtime?
No; battery energy controls runtime.