Generator Wattage Calculator
Size a generator from the running watts and surge watts of the appliances you want to power.
Add up the equipment loads, then use the result to compare generator capacities and apparent power.
| Appliance | Running watts | Surge watts |
|---|---|---|
| Appliance 1 | ||
| Appliance 2 | ||
| Appliance 3 | ||
| Appliance 4 | ||
| Appliance 5 |
Result
--
Run the calculation to see the generator size.
| Metric | Value |
|---|---|
| Total running watts | -- |
| Total surge watts | -- |
| Recommended generator watts | -- |
| Apparent power | -- |
Quick Answer
Add the running and surge watts of the appliances you want to power. The safest generator estimate is usually the total surge wattage, adjusted for power factor and capacity margin.
How to Calculate
- Enter the running and surge watts for each appliance.
- Choose a power factor and utilization target.
- Click Calculate.
- Compare the result with available generator sizes.
Formula
Total running watts = sum of running watts
Total surge watts = sum of surge watts
Apparent power = generator watts / power factor
Worked Examples
Example 1: A refrigerator, fan, lights, and TV can require a few thousand surge watts together.
Example 2: A generator with a 0.8 power factor needs more apparent power than its running watt number suggests.
Example 3: Keeping a 25 percent capacity margin makes room for future appliances.
How to Interpret Your Results
| Output | Meaning | Action |
|---|---|---|
| Total surge watts | The best practical estimate for generator sizing. | Use it as the main target. |
| Apparent power | Adjusted generator size after power factor. | Compare this to generator ratings. |
| Utilization target | How much of the generator you plan to use. | Lower utilization gives more headroom. |
Frequently Asked Questions
Related Calculators
References
- OmniCalculator reference page
- Generator sizing should account for both running and surge watts.
- Last reviewed: March 2026.