What is the difference between running watts and starting watts?

Running watts (continuous watts) is the steady power an appliance needs while operating. Starting watts (surge watts) is the brief spike needed to start motors — typically 2–3× the running wattage. Your generator must handle both: enough running watts for continuous load and enough surge capacity for the highest starting spike.

Why does the recommendation add 25% headroom?

Running a generator at 100% capacity shortens its lifespan and can cause voltage instability. The 1.25× multiplier on starting watts keeps the generator comfortably within its rated capacity and leaves room for minor loads you may have forgotten.

Can I run all appliances at the same time?

Only if your generator's rated wattage exceeds the total starting wattage shown. If not, stagger startup: turn on the highest-surge appliance first, let it stabilize, then start the next. Refrigerators, AC units, and sump pumps have the biggest surge spikes.

What generator class should I choose?

Portable generators (under 4,000 W) cover lights, small appliances, and a phone charger. Mid-range (4,000–7,500 W) handles a refrigerator, window AC, and several circuits. Standby generators (over 7,500 W) are installed permanently and can power most of a home automatically during an outage.

Are these appliance wattage values accurate?

The preset values are typical averages. Actual draw varies by brand, age, and load. Check your appliance's nameplate or owner's manual for the exact rating, then use Manual Entry mode to enter the precise value.

Generator Wattage Calculator

Name: Generator Wattage Calculator
Availability: InStock
Author: Nham Vu

Add appliances or enter wattage manually to find out what generator size you need.

Check every appliance you plan to run simultaneously.

Generator Recommendation

Running Watts

W continuous

Starting Watts

W peak surge

Recommended Generator

0 W

starting watts × 1.25 headroom

Enter appliances to see generator class

Summary

Add appliances or enter wattage manually to find out what generator size you need.

How it works

Choose the Appliance List tab to pick from common appliances, or switch to Manual Entry to type in your own wattage values.
Check the boxes next to each appliance you plan to run at the same time.
The tool sums running watts and starting (surge) watts and applies a 1.25× safety buffer.
Read the recommended generator size and class (portable, mid-range, or standby).

Use cases

Plan a backup generator for home power outages.
Size a portable generator for a job site or camping trip.
Check whether an existing generator can handle a new appliance.
Compare running load vs. peak surge to avoid tripping the generator.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu