Generator Sizing by Scenario
What Size Generator for a 1,000 Sq Ft House?
A 1,000 sq ft home typically needs 3,500–5,500 watts for essential backup. This covers a refrigerator, sump pump, furnace blower (gas heat), lights, TV, and phone charging. If you also want a window AC unit for a small bedroom, budget 5,000 watts minimum.
What Size Generator for a 2,000 Sq Ft House?
A 2,000 sq ft home with gas appliances and a gas furnace needs 5,000–7,500 watts for essentials. Add central air conditioning and the requirement jumps to 12,000–15,000 watts. Many homeowners with 2,000 sq ft homes choose a 7,500-watt portable generator for essential-only backup, or a 14–16 kW standby generator for full coverage.
What Size Generator for an RV?
The RV AC unit is the primary sizing driver. A 13,500 BTU rooftop AC needs 1,500W running and up to 4,000W to start. Without a soft-start kit: you need a 3,500W minimum generator. With a soft-start kit (recommended): a 2,200–2,500W inverter generator can handle the AC. Add 700–1,000 watts for an RV microwave, 200–300W for TV and lighting, and you arrive at 3,000–4,500 watts total for comfortable RV use.
What Size Generator for a Sump Pump and Refrigerator?
Running just a sump pump (up to 3,150W surge) and refrigerator (up to 1,200W surge) together requires a generator that can handle these surges without tripping. The surges don't happen simultaneously, but your generator must handle each independently. A 3,500-watt generator can do this, though a 5,000-watt unit gives better headroom and lets you add lights and phone charging.
What Size Generator for a Well Pump?
A 1 HP shallow well pump surges to 2,100–2,400 watts. A 1.5 HP deep-well submersible pump surges to 3,150–3,600 watts. For a well pump alone, a 3,000-watt generator is the minimum. For a well pump plus refrigerator, sump pump, and lights, plan for 5,500–7,500 watts.
Understanding the 80% Capacity Rule
Every generator has a rated (running) wattage — the maximum continuous load it's designed to sustain. However, running any generator at exactly 100% capacity is not recommended. The standard guideline is to plan for no more than 80% of rated capacity as your sustained load.
Why? Operating at 100% causes excessive heat buildup, higher fuel consumption, accelerated engine wear, and increases the risk of overloading when any appliance has a brief surge. The 80% rule gives you a safety buffer that extends engine life and improves reliability.
In practice, this means: if your appliances total 4,000 running watts, you should buy a generator rated for at least 5,000 watts (4,000 ÷ 0.8 = 5,000). Our calculator applies this rule automatically in its recommendations.
Quick Reference: Generator Size Summary
| Generator Size | What It Can Power | Best For |
|---|---|---|
| 1,000–2,000W | Phone charging, laptop, LED lights, small fan, 12V cooler | Camping, tailgating |
| 2,500–3,500W | Above + RV AC (with soft-start), refrigerator | RV camping, essential backup |
| 3,500–5,000W | Refrigerator, sump pump, lights, fans, TV | Home essential backup |
| 5,000–7,500W | Above + window AC, well pump, most home circuits | Home comfort backup |
| 7,500–10,000W | Above + small central AC, more circuits simultaneously | Large home essentials |
| 10,000–14,000W | Most home circuits except electric dryer and large central AC | Near-whole-home coverage |
| 14,000–22,000W | Complete whole-home coverage including central HVAC | Whole house standby |
For a personalized recommendation, use the calculator above or navigate to our specialized pages: home generator calculator, portable generator calculator, or whole house generator calculator.
