What Size Generator Do I Need?
For most homes, you need a 5,000 to 7,500 watt portable generator for essential circuits (fridge, lights, sump pump, WiFi), or a 15,000+ watt standby generator for whole-home backup including central AC.
Use the calculator below to get an exact recommendation based on the appliances you need to power, or scan the quick reference table for common scenarios.
Generator Sizing Calculator
Select your use case, check the appliances you need to power, and get an instant recommendation.
Step 1: What are you powering?
Quick Reference: What Size Generator Do I Need?
Skip the calculator. Find your scenario and get the answer.
| If You Need To Power... | You Need At Least... | Generator Type |
|---|---|---|
| Phone, laptop, lights, small devices | 2,000W | Portable Inverter |
| Fridge + lights + sump pump + WiFi | 3,500–5,000W | Portable |
| Fridge + window AC + essentials | 5,000–7,500W | Portable |
| Most home appliances (no central AC) | 7,500–10,000W | Portable |
| Full home backup with central AC | 15,000–22,000W+ | Standby |
| RV with AC | 3,500–5,000W | Portable Inverter |
| Jobsite power tools | 5,000–7,500W | Portable |
Frequently Asked Questions
What size generator do I need for my house?
Most homes need a 5,000–7,500W portable generator for essentials (fridge, lights, sump pump, WiFi) or a 15,000–22,000W+ standby generator for whole-home backup with central AC.
What size generator do I need to run a refrigerator?
A refrigerator needs about 150 running watts but up to 1,200 starting watts. A 2,000W generator handles a fridge easily with room to spare for lights and phone chargers.
What size generator do I need for an RV?
3,500–5,000W covers most RVs including AC. Get an inverter generator for clean power that protects sensitive electronics like TVs and laptops.
What size generator to run a window air conditioner?
A 10,000 BTU window AC needs about 1,200 running watts and 3,600 starting watts. A 5,000W generator handles one window AC unit plus other essentials.
What is the difference between running watts and starting watts?
Running watts measure continuous power draw during normal operation. Starting watts measure the brief surge when a motor kicks on, typically 2–3x higher than running watts. Your generator must handle the highest starting surge on top of everything else running.
Can I run my central AC on a portable generator?
Central AC needs 10,500+ starting watts. You need a standby generator (15,000W+) or a very large portable (12,000W+). Most standard portable generators can't handle central AC.
How long will a generator run on a tank of gas?
Most portable generators run 8–12 hours at 50% load on a full tank. Inverter generators with eco-mode can stretch to 10–18 hours. Larger tanks and lower loads mean longer runtime.
Inverter generator vs conventional generator — what's the difference?
Inverter generators produce cleaner power (safe for electronics), run quieter (48–58 dB vs 70+ dB), weigh less, and use less fuel. They cost more and usually max out around 7,000W. Conventional generators are louder but cheaper and available in higher wattages.
What size generator do I need for a construction site?
5,000–7,500W for basic power tools like drills and circular saws. 10,000W+ if running multiple tools simultaneously or heavy equipment like an air compressor.
Do I need a transfer switch?
Yes, if connecting a generator to your home's electrical panel. A transfer switch prevents backfeeding into power lines, which is illegal and dangerous. Professional installation typically costs $200–$500.