Generator Sizing Calculator
Calculate the right generator size for your appliances. Account for running and starting watts to avoid undersizing.
Appliance Power Calculator
Running Watts vs Starting Watts
Running watts = continuous power. Starting watts = that surge when a motor fires up. A 7,500-watt portable will run your fridge, well pump, and a few lights. But try starting the AC and the well pump at the same time? That starting surge will trip the breaker. Stagger your loads.
Motors pull 2-4 times their running current at startup because the rotor isn't spinning yet. Your generator has to handle that spike or everything shuts down. Undersized and the overload trips instantly.
Get It Right, Not Oversized
- Too Small: Breaker trips, nothing runs, you're sitting in the dark
- Right Size: Everything runs, good voltage, reliable. Add some reserve so startup surges and real-world load swings do not trip the generator.
- Too Big: Costs more, burns fuel inefficiently, poor at partial loads
Portable vs Standby (What You Actually Need)
| Type | Power Output | Typical Cost | Best Use |
|---|---|---|---|
| Portable (Small) | 3,500-10,000W | $500-$2,000 | Temporary power, jobsites, RVs |
| Portable (Large) | 10,000-20,000W | $2,000-$5,000 | Whole-home backup for days |
| Standby (Permanent) | 10,000-100,000W | $5,000-$20,000+ | Automatic, always ready, no setup |
Real Appliance Power Needs
Fridge: 600W running, 2,200W when it starts. Well pump: 800W running, 3,000W starting. AC unit: 3,500W running, 6,000W starting. Most homes need 10,000-15,000W for full backup, though smaller portables work if you're just covering essentials.
