Inverter Sizing Calculator
Minimum inverter rating for a set of AC loads.
Enter your values
Enter the total running load in W.
Enter the largest surge/starting load in W.
Enter the safety margin in %.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Minimum continuous rating
- 960 W
- Minimum surge rating
- 1650 W
- Recommended inverter size
- 1650 W
Quick answer
Inverter continuous rating should exceed total running watts x safety margin.
Inverter rating >= total load x margin
At a glance
| What it does | Minimum inverter rating for a set of AC loads. |
|---|---|
| Category | Engineering |
| Inputs needed | Total running load, Largest surge/starting load, Safety margin |
| Main output | Minimum continuous rating |
| Formula | Inverter rating >= total load x margin |
| Cost | Free — no sign-up, no download |
How to use the Inverter Sizing Calculator
- 1Add up the running wattage of all devices to run simultaneously.
- 2Identify the single largest surge load (motors and compressors draw 2-3x their running watts at startup).
- 3Choose an inverter that comfortably covers both figures with margin.
Inputs explained
- Total running load(W)
- Enter the total running load in W.
- Largest surge/starting load(W)
- Enter the largest surge/starting load in W.
- Safety margin(%)
- Enter the safety margin in %.
Worked example
Using the values the calculator loads with:
Inputs
- Total running load800 W
- Largest surge/starting load1500 W
- Safety margin20 %
Results
- Minimum continuous rating960 W
- Minimum surge rating1650 W
- Recommended inverter size1650 W
Frequently asked questions
Why is surge rating important?
Motors, pumps and compressors need a brief high-current surge to start; an undersized inverter will trip or fail.
Pure sine vs modified sine?
Sensitive electronics and motors run better and last longer on pure sine wave inverters.
What do I need to enter into the Inverter Sizing Calculator?
Just 3 values: total running load, largest surge/starting load, safety margin. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Inverter Sizing Calculator work out the answer?
Inverter continuous rating should exceed total running watts x safety margin. It applies the formula Inverter rating >= total load x margin and shows the working so you can check each step by hand.
Is the Inverter Sizing Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.