PickMyWatt

Inverter Generator Size Calculator

Inverter generators produce clean, stable power ideal for sensitive electronics. Use this calculator to find the right size and estimate fuel costs based on your appliance selection.

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Sensitive Electronics
Safe for laptops, phones, TVs, and medical devices with less than 3% THD clean power output.
🤫
Quiet Operation
Typically 50-65 dB, much quieter than conventional generators. Perfect for campgrounds and neighborhoods.
⛽
Fuel Efficient
Eco-mode adjusts engine speed to load, using 20-40% less fuel than conventional generators.
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Parallel Ready
Most inverter generators can be linked in parallel. Two 2,200W units give you 4,400W when needed.
W
NEC 80% Rule: Per NEC 210.20(A), continuous loads (running 3+ hours) should not exceed 80% of rated capacity. Your 3,500W generator safely handles 2,800W continuous load.

Your appliances

Running W = normal draw · Starting W = motor startup surge · Contruns 3+ hours (NEC continuous load) · Non-Contshort duty

W
W
W
W
W
W
W
W
3 appliances · 1,850W running
Generator Size
3,500W
watts
Load Status67%
NEC Load: 1,888WUsable: 2,800W
Refrigerator150/600WCont
Microwave (1000W)1,200WNon-Cont
Washing MachineMAX SURGE500/1,200WNon-Cont

Fuel Cost Estimate

gal
Price
$$/gal
Hours/Day8h
Diversity?75%
Avg Load?
3%
Rate: 0.075 gal/kW/hr. Sources: Generac, Honda, US EIA
Per Hour
$0
Per Day
$0
Per Month
$6
Calculation breakdown
Base Load: 150W ÷ 3,500W = 4%
Avg Load: 4% × 75% = 3%
Fuel/hr: 3.5 kW × 0.075 × 3% = 0.01 gal/hr
Cost/hr: 0.01 × $3.00 = $0.02/hr
Cost/day: $0.02 × 8h = $0/day
Cost/month: $0 × 30 = $6/mo

PickMyWatt.com

Inverter Generator Size Calculator

Your Generator
3,500
watts
Load: 67%
Continuous
150W
Non-Cont
1,700W
Starting Surge
700W

Selected Appliances

Refrigerator150/600W
Microwave (1000W)1,200W
Washing MachineMAX SURGE500/1,200W
Fuel Cost Estimate
Per Hour
$0.02
Per Day
$0
Per Month
$6
gasoline

Calculated with PickMyWatt.com

NEC Article 220 Compliant

Calculation Standard: Based on NEC Article 220 load calculation principles. Continuous loads (>3 hours) sized at 125% per NEC 210.20(A). Non-continuous loads use only the largest expected simultaneous load.
Data Sources: Energy Star, DOE, Manufacturer specs (Generac, Honda, Champion, Kohler)

Why Choose an Inverter Generator?

An inverter generator produces clean, stable electricity with less than 3% Total Harmonic Distortion (THD), making it safe for sensitive electronics like laptops, smartphones, TVs, and medical devices. Unlike conventional generators that run at a fixed speed, inverter generators adjust their engine speed to match the electrical load — resulting in quieter operation and better fuel efficiency.

Inverter Generator Size Guide

SizeWattsBest ForWeight
Ultra-light1,000-2,200WCamping, tailgating, phone/laptop charging30-50 lbs
Mid-size2,500-3,500WRV, small home backup, fridge + window AC50-80 lbs
Large4,000-5,000WHome backup essentials, job site tools80-120 lbs
Extra-large6,000-7,600WExtended home backup, multiple appliances120-200 lbs

Inverter vs Conventional Generator: Key Differences

FeatureInverterConventional
Power Quality (THD)<3% — safe for electronics5-15% — may damage sensitive devices
Noise50-65 dB (conversation level)65-80 dB (lawnmower level)
Fuel Efficiency20-40% better (variable speed)Fixed speed, always at full RPM
Runtime per Tank8-18 hours6-12 hours
Price30-50% more expensiveLower upfront cost
Max WattageUp to 7,600W (single unit)Up to 15,000W+

How to Calculate the Right Size

Use our calculator above to select your appliances. The calculator applies NEC 210.20(A) continuous load sizing and accounts for motor starting surges. For inverter generators, pay special attention to starting watts — the eco-mode feature means the generator ramp up to handle surges, so starting watt capacity matters more than with conventional units.

Parallel Operation: Doubling Your Power

Most inverter generators support parallel connection, allowing you to link two identical units for double the wattage. For example, two Honda EU2200i units can produce 4,400W together. This gives you flexibility: use one unit for light loads, connect both when you need more power. Note: you typically need a parallel kit from the same manufacturer.

Frequently Asked Questions

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References & Sources