A generator's amp output depends on its wattage and voltage. At 120V, a generator produces 1 amp for every 120 watts. At 240V, it produces 1 amp for every 240 watts. A 7,500W generator delivers 62.5 amps at 120V or 31.25 amps at 240V. A 22,000W standby generator delivers approximately 183 amps at 120V or 91.7 amps at 240V.
The formula is simple: Amps = Watts ÷ Volts. But applying it correctly — accounting for starting surges, 120V vs. 240V circuits, and generator outlet ratings — is where most people get confused. This guide gives you the complete amp output chart and explains exactly how to match your generator's amperage to your electrical needs.
Interactive Amps/Watts Calculator
Convert between generator watts, amps, and voltage with wire size recommendations:
Generator Amp Output Chart
120V vs. 240V: Most household outlets are 120V (standard three-prong). Large appliances like central AC, electric dryers, electric ranges, and well pumps use 240V circuits. A generator's total amp capacity is split between these voltages. A 7,500W generator can deliver 62.5A total at 120V, OR 31.3A at 240V, OR a combination of both — but never 62.5A at 120V and 31.3A at 240V simultaneously.
The Watts-Amps-Volts Formula
Amps = Watts ÷ Volts
This is Ohm's Law applied to electrical power, and it is the foundation of all generator sizing.
Example — Can my 7,500W generator run a 30-amp RV? A 30-amp RV outlet operates at 120V. Maximum power: 30A × 120V = 3,600W. Your 7,500W generator produces 62.5A at 120V, which is more than enough for a 30A RV connection. You still have roughly 32.5A (3,900W) available for other 120V loads.
Example — Can my 5,500W generator run a 240V well pump? A typical ½ HP well pump draws about 10A at 240V (2,400W running) with a starting surge of about 17A (4,080W). Your 5,500W generator at 240V delivers 22.9A continuous — enough for the running load but the starting surge at 4,080W is close to the generator's capacity. It should work, but it will be at 74% of the generator's capacity during startup. A 7,500W generator provides much more headroom.
Example — What size generator for a 200-amp house panel? A 200-amp panel at 240V has a maximum capacity of 200A × 240V = 48,000W. However, no home runs at 100% panel capacity simultaneously. Typical peak demand for a 200-amp home is 40–60% of panel capacity, or 19,200–28,800W. A 22–24kW standby generator covers most 200-amp homes with load management.
Generator Outlet Types and Amp Ratings
Portable generators have specific outlet configurations, each rated for a maximum amperage. Understanding these outlets tells you exactly how much power you can draw from each connection.
Never exceed an outlet's amp rating. Plugging a 40A load into a 30A outlet causes overheating, wire damage, and fire risk. If you need more amps than a single outlet provides, use the generator's larger outlet (L14-30R or L14-50R) with an appropriate transfer switch, or distribute loads across multiple outlets.
How Many Amps Do Common Appliances Draw?
Knowing each appliance's amp draw helps you plan which circuits to power and verify you are not exceeding your generator's capacity.
Wire Gauge for Generator Connections
Using the correct wire gauge prevents overheating and ensures safe power delivery from your generator to your transfer switch or appliances.
Extension cord safety: For portable generators, use the shortest, heaviest-gauge extension cord possible. A 100-foot, 16-gauge extension cord can lose 10–15% of voltage at high loads, causing appliance damage and overheating. For 20A loads, use 10-gauge or 12-gauge cords no longer than 50 feet. Never daisy-chain extension cords.
Understanding Your Electrical Panel
Your home's main panel has a rating (typically 100A or 200A at 240V) that represents the maximum amperage it can handle from the utility. When connecting a generator via a transfer switch, you need to understand how the generator's amperage relates to your panel.
You almost never need a generator that matches your panel's maximum capacity. A 200-amp panel can theoretically draw 48,000W, but a typical home rarely exceeds 30–40% of panel capacity even during peak use. A 22kW standby generator with load management handles most 200-amp homes.
Real-World Example — Matching Generator to Panel: A homeowner with a 200A panel consulted an electrician who measured their actual peak load at 18,500W during a hot summer afternoon (AC + water heater + oven + dryer running). A 22kW standby generator (91.7A at 240V) covers that peak with room to spare. The 200A ATS passes through utility power at full 200A capacity during normal operation and switches to generator power during outages.
Key Takeaways:
- Amps = Watts ÷ Volts. A 7,500W generator produces 62.5A at 120V or 31.3A at 240V.
- A 22kW standby generator delivers ~183A at 120V or ~92A at 240V.
- Always account for starting amps — motors draw 1.5–5x their running amps during startup.
- Generator outlets have specific amp ratings (20A, 30A, 50A) — never exceed them.
- A 200-amp panel does not need a 48kW generator. Typical peak demand is 30–40% of panel capacity.
- Use correct wire gauge: 10 AWG minimum for 30A connections, 6 AWG for 50A.
- Never daisy-chain extension cords or use cords too small for the load.
Frequently Asked Questions
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