What this calculator does
The Small Business Generator Size Calculator helps shop owners, restaurants, clinics, studios, offices, small warehouses, and service businesses build a practical outage plan. The question is not simply “what size generator do I need?” The better question is: which loads are critical, what are their running watts, and which devices create a starting surge?
A small business outage plan often prioritizes refrigeration, point-of-sale systems, internet, security, lighting, phone charging, critical computers, medical or shop equipment, and limited comfort cooling or ventilation. Trying to power everything can make the generator far larger and more expensive than necessary.
Quick answers
How to estimate generator size
This calculator assumes the largest motor starts while other critical loads are already running. In real installations, staged startup can reduce required generator size.
| Load type | Planning note |
|---|---|
| Refrigerators and freezers | Usually critical for food, medical, or inventory protection; check compressor surge. |
| POS and internet | Small wattage, but essential for sales, payments and communication. |
| Lighting | LED lighting can reduce generator load compared with older fixtures. |
| HVAC | Often one of the largest loads; decide whether it is truly critical during an outage. |
| Kitchen equipment | Heating appliances can be very power-hungry and may require a much larger generator. |
How to build a critical-load plan
- List everything you want to run during a power outage.
- Mark each item as must-run, nice-to-have, or shut off.
- Use nameplate watts or manufacturer specifications when possible.
- Identify motors and compressors that need starting surge allowance.
- Plan safe generator placement, extension rating, transfer switch, fuel storage and staffing procedures.
- Test the plan before storm season or before the next known outage risk.
Example
A small shop may need refrigeration, POS, router, lighting and one computer. A restaurant may need refrigeration plus selected kitchen equipment, which can dramatically increase generator size. An office may need internet, servers, lights and a few workstations but not full HVAC.