Inverter Size Calculator
Calculate the recommended inverter size for your load with a margin for losses and headroom.
Size for continuous load only. Motors, compressors, and pumps draw 2–3× their running wattage on startup — verify the inverter's peak (surge) rating against your highest inrush load. Consult a qualified electrician before installation.
How it works
- 1Enter the total continuous load in watts — all devices running at once.
- 2Set the sizing margin (default 25%) for inverter efficiency losses and headroom.
- 3The calculator multiplies load by the margin factor for the minimum recommended rating.
Use cases
- Sizing an off-grid or solar backup inverter for a cabin or home.
- Selecting an inverter for an RV, van, or boat electrical system.
- Choosing an inverter for critical office or workshop loads.
Frequently asked questions
Why do I need a sizing margin?
Inverters run best at 50–80% of rated capacity. A 25% margin keeps the unit in its efficient band and leaves room for brief spikes.
Does this account for motor surge?
No — it sizes for continuous watts only. Motors and compressors can draw 2–3× their running watts at startup; check the inverter’s separate peak/surge rating.
Worked example: 1200 W load with 25% margin?
1200 W × 1.25 = 1500 W. Choose the next standard size up (1500 W or 2000 W), leaving about 300 W of headroom.
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