Generator Size Calculator

Calculate generator wattage needed based on appliances. Accounts for starting watts on motor loads.
Select Appliances to Power

Use the Generator Size Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.

Disclaimer: This calculator is for informational purposes only and does not constitute tax, financial, or legal advice. Results are estimates based on the information you provide and current rates. Always consult a qualified tax professional or financial advisor for advice specific to your situation.

How It Works

Our 2026 Generator Size Calculator helps you determine the precise wattage your generator needs to power your essential appliances. Avoid costly over-sizing or frustrating under-sizing by accounting for both running and crucial starting wattages, especially for motor-driven devices.

This calculator sums the running watts for all selected appliances. For motor-driven appliances, it identifies the highest starting wattage among them and adds it to the total running wattage, as only one motor typically starts at a time. This provides the minimum required surge wattage.

A common mistake is only considering running watts; motor loads like refrigerators or air conditioners require significantly more wattage to start. Always factor in a 10-20% buffer for future needs or unexpected loads. Don't forget small but numerous loads like phone chargers or LED lighting.

Example: Home Backup Scenario

  1. 1 Input your appliances: Refrigerator (700 running, 2200 starting watts), Microwave (1500 running, 1500 starting watts), 50-inch Smart TV (120 running, 120 starting watts), 10 LED Light Bulbs (10 watts each, 100 running total).
  2. 2 Calculate: Total running watts = 700 + 1500 + 120 + 100 = 2420 watts. Highest starting wattage (from refrigerator) = 2200 watts. Therefore, required surge wattage = 2420 (running) + 2200 (highest starting) = 4620 watts. Continuous running wattage = 2420 watts.
  3. 3 Result: You need a generator capable of at least 2420 continuous running watts and 4620 surge (starting) watts. A 5000-watt generator would provide a comfortable buffer.
  4. 4 Context: This calculation ensures your generator can handle the initial power spike when a major appliance, like your refrigerator, kicks on, preventing overload and ensuring continuous power for your other devices. Always consult your appliance manuals for exact wattage figures.

Source: DOE · Last updated: April 2026

Frequently Asked Questions

What size generator do I need for my house?
Most homes need a 7,500 to 10,000 watt generator for essentials like the fridge, sump pump, lights, and a few outlets. A whole-house standby generator for central air and all circuits typically requires 20,000 to 25,000 watts.
What is the difference between running watts and starting watts?
Running watts is the continuous power an appliance uses during normal operation. Starting watts (or surge watts) is the extra power needed for the first few seconds when a motor starts, typically 2-3 times the running watts.
Can a generator run a central air conditioner?
Yes, but a 3-ton central AC unit requires about 3,500 running watts and 4,500-6,000 starting watts. You need at least a 7,500-watt generator to run AC along with other basic loads.

You might also need

Solar Panel Savings Calculator

Estimate solar panel system cost, payback period, and 25-year savings with federal tax credit and state incentives.

Electricity Bill Calculator

Calculate your monthly electricity bill by adding appliances and their usage. Find your biggest energy consumers.

Carbon Footprint Calculator

Estimate your annual carbon footprint from driving, electricity, flights, and diet. Compare to the US average.