Generator Wattage Calculator

Calculate your total running watts and starting surge watts by adding appliances below to find the right generator size for your home, RV, or jobsite.

Quick Load Presets (1-Click Sizing): Click to instantly populate realistic power scenarios
Advertisement

Appliance Library

Tap + to add

Add Custom Item

Required Generator Size

0 Watts

Based on Running Watts + Highest Surge

Total Running

0 W

Peak Surge

0 W

Recommended Type

--
View Matching Generators AMAZON

Check live prices, discounts & ratings

Your Load List (0)

Your list is empty.

Add items from the library.

Generator Wattage Chart

Common wattage requirements for household appliances and tools. Use this chart as a reference guide.

Appliance Wattage Reference

Appliance Running Watts Starting Watts

How to Calculate Generator Sizing: Running vs. Starting Watts

Selecting the right generator size depends on two key electrical requirements: continuous running watts and initial motor starting surge watts.

Generator Wattage Calculator Guide - Running Watts vs Starting Surge Watts Diagram

Illustration: Understanding Running (Continuous) Watts vs Starting (Surge) Watts for Household Appliances & Equipment

Running (Rated) Watts

The continuous electrical power required to keep equipment operating after startup. Resistive devices like lights, heaters, and toasters only draw running watts.

Starting (Surge) Watts

The momentary extra burst of power (lasting 2–3 seconds) needed for electric motors and compressors (refrigerators, sump pumps, central AC) to start from a dead stop.

Standard Generator Sizing Formula

Sum all continuous running loads, add the single largest starting surge, and include a 15% to 20% safety buffer:

Generator Capacity = ( Total Running Watts + Largest Starting Surge ) × 1.20

Common Generator Size Applications

2,000W – 3,500W

Inverter / Tailgating & RV

Runs refrigerator, LED lighting, TV, laptops, and small kitchen appliances.

5,000W – 7,500W

Emergency Home Backup

Powers refrigerator, 1/2 HP sump pump, microwave, window AC, and home office.

9,000W – 13,000W+

Whole-House System

Connects to transfer switch for central AC (with soft start), well pump, and electric range.

Frequently Asked Questions

For essential circuits (refrigerator, lights, sump pump, router, and microwave), a 5,000 to 7,500-watt generator is usually ideal. If you want to power a central air conditioning unit or well pump, you typically need 9,000 to 12,000+ watts.
Running a generator at 100% capacity for extended periods causes engine strain, excessive fuel usage, and voltage instability. Operating around 70% to 80% load improves engine life and accommodates sudden startup surges.
Yes, but central AC units have high starting surge requirements. Adding a soft-starter device to your AC compressor reduces startup surge significantly, allowing a 7,500W to 9,500W generator to start the AC smoothly.
Use the formula: Watts = Volts × Amps. For standard 120V household outlets, multiply 120 by the amp draw (e.g. 120V × 10A = 1,200W). For heavy-duty 240V equipment, multiply 240 by the amp draw.

Share This Calculator

Help friends & colleagues calculate generator wattage accurately.