How we estimate generator size (methodology & sources)
Our sizing tool turns a use case into a kW range using wattages published by generator manufacturers and rental companies. We show a range, not a single number, because real equipment varies. Always confirm with the rental company.
The math
- Add the running watts of everything that runs at the same time (low and high ends of each published range).
- Add the single largest start-up surge (starting minus running watts of the biggest motor load), as Generac's and Champion's guides describe; where a source states a surge for a device (Del Rey: a DJ setup adds 1,500 W at start-up), we use the larger of the two.
- Multiply by 1.2 for a 20% safety buffer and divide by 1,000 for kW (Del Rey Party Rentals, steps 5–6). The result is rounded up to the next 0.5 kW.
The American Red Cross describes the same approach: add device watts, divide by volts for amps, and choose a generator that produces more than you need because some machines draw up to 3 times as much power when starting (American Red Cross: Generator Safety).
Type, fuel and extras (rules of thumb)
- Up to about 7 kW: portable, inverter when noise matters. Lightbulb Rentals describes quiet inverter generators of 2–7 kW for small film runs, and Champion's food-truck guide lists inverter or portable units up to 10,000 W.
- About 7–12 kW: large portable or small towable unit.
- Above about 12 kW: towable, trailer-mounted unit, typically diesel. Del Rey books 15–20 kW for a tented wedding and 20–50 kW+ for large outdoor events; Stag Power Rentals lists 50–150 kW for commercial and small film shoots.
- Distribution: cables sized for the load; distribution panels and Cam-Lok cables on larger units (San Diego Film Equipment pairs its 500 A tow plant with production cable, lunch boxes and Cam-Lok distribution). Del Rey notes voltage drop becomes a real problem beyond 50 feet on standard extension cords.
- Home use: power house circuits only through a transfer switch installed by an electrician; never backfeed through an outlet (American Red Cross: Generator Safety).
These thresholds are our editorial rules of thumb based on the sources above, not a standard. A rental company may recommend differently for your site.
Every wattage we use
| Item | Running W | Starting W |
|---|
| Outdoor light string (per string) | 250 | — |
| Item | Running W | Starting W |
|---|
| Uplight (each; 8 uplights = 400 W in the source example) | 50 | — |
| Chandelier (each) | 100–300 | — |
| DJ setup (speakers + mixer) | 1,000–2,000 | +1,500 surge |
| PA sound system | 500–2,000 | — |
| LED screen / video display | 200–500 | — |
| Holding & warming cabinet (each) | 1,000–1,500 | — |
| Electric grill / griddle (catering) | 1,200–2,000 | — |
| Catering cooking equipment (full setup) | 1,500–3,000 | — |
| Tent heater, LB White LB80 (each) | 1,500–2,000 | — |
| Tent heater, LB White LB170 (each) | 2,000–2,500 | — |
| Misting / cooling fan (each) | 50–300 | — |
| Item | Running W | Starting W |
|---|
| Coffee brewer | 800–1,500 | — |
| Commercial refrigerator | 600–800 | 2,000 |
| Air conditioner, 13,500 BTU (each) | 1,500–2,000 | 3,500 |
| POS system / register | 50–150 | — |
| LED interior lighting | 20–100 | — |
| Exterior menu / sign lighting | 50–200 | — |
| Commercial refrigerator | 600–800 | 2,000 |
| Commercial freezer | 700–1,000 | 2,500 |
| Ice maker | 300–700 | 1,200 |
| Vent hood / exhaust fan | 300–600 | 900 |
| Fresh water pump | 100–300 | 600 |
| Electric griddle | 1,500–3,000 | — |
| Electric deep fryer | 1,800–5,000 | — |
| Induction cooktop | 1,500–3,500 | — |
| Panini press | 1,000–1,800 | — |
| Microwave (commercial) | 1,000–1,800 | 2,200 |
| Espresso machine | 1,500–3,000 | — |
| Blender | 500–1,500 | 2,000 |
| Air conditioner, 13,500 BTU | 1,500–2,000 | 3,500 |
| Item | Running W | Starting W |
|---|
| Refrigerator | 150–400 | 1,200 |
| Freezer | 100–500 | 1,000 |
| Window AC, 10,000 BTU | 900–1,200 | 2,400 |
| Central AC, 3 ton | 3,000–3,500 | 6,000 |
| Sump pump, 1/2 HP | 800–1,050 | 2,150 |
| Well pump, 1 HP | 1,000–2,000 | 4,000 |
| Well pump, 1/2 HP | 750–1,000 | 2,000 |
| Furnace fan, 1/2 HP | 300–800 | 1,600 |
| Microwave | 600–1,200 | — |
| Electric water heater | 3,000–4,500 | — |
| Space heater | 750–1,500 | — |
| TV (32"–55") | 80–400 | — |
| LED light bulb (each) | 8–15 | — |
| Internet router / modem | 10–20 | — |
| CPAP with heated humidifier | 60–120 | — |
| Phone / laptop charger (each) | 20–100 | — |
| Washing machine | 500–1,000 | 2,300 |
| RV air conditioner, 13,500 BTU | 1,500–2,000 | 3,500 |
| RV air conditioner, 15,000 BTU | 2,000–2,500 | 4,500 |
| RV refrigerator | 150–600 | 1,000 |
| RV microwave | 600–1,200 | — |
| RV water heater | 1,200–1,500 | — |
| String lights / LED camp lights | 50–200 | — |
| CPAP (without heat) | 30–60 | — |
| Circular saw, 7-1/4" | 1,200–1,800 | 3,600 |
| Table saw, 10" | 1,800–3,000 | 6,000 |
| Miter saw, 10" | 1,200–1,800 | 3,600 |
| Angle grinder, 4-1/2" | 900–1,800 | 3,600 |
| Hammer drill | 900–1,200 | 2,400 |
| Air compressor, 1 HP | 1,500 | 4,500 |
| Air compressor, 2 HP | 2,500 | 7,500 |
| Pressure washer, 2,500 PSI | 2,000–2,500 | 5,000 |
| Work light, halogen 500 W | 500 | — |
| Welder (120 V) | 1,800–2,500 | 5,000 |
| Welder (240 V) | 3,000–8,000 | 16,000 |
| Job-site heater | 1,500–3,000 | — |
| Battery charger (heavy duty) | 1,500–2,000 | — |
| Item | Running W | Starting W |
|---|
| LED fixture, Aputure 600x class (each) | 720 | — |
| LED tube, Astera class (each; 4 ≈ 290 W) | 72–73 | — |
| Monitors + chargers (video village) | 200 | — |
Reference sizes shown next to estimates
- Small backyard party (lights + speaker + fans): 2,000–4,000 W load, book 5–6 kW (Del Rey Party Rentals)
- Mid-size outdoor birthday or graduation (DJ + bistro lights + catering): 5,000–8,000 W load, book 10 kW (Del Rey Party Rentals)
- Tented wedding (full lighting + DJ + catering + heaters): 8,000–15,000 W load, book 15–20 kW (Del Rey Party Rentals)
- Large outdoor corporate or social event: 15,000–30,000+ W load, book 20–50 kW+ (Del Rey Party Rentals)
- Commercial & small film shoots: 50–150 kW (Stag Power Rentals)
- TV & mid-size productions: 150–300 kW (Stag Power Rentals)
- Large film productions: 300–800 kW (Stag Power Rentals)
Sources
Sources fetched October 22, 2026.