# Generator Size Calculator

Determine the right generator size for your needs. Select appliances to calculate running watts, starting watts, and get a generator size recommendation.

## What this calculates

Preparing for a power outage or need a generator for a job site? Select the appliances and devices you want to power, and this calculator totals the running and starting wattage to recommend the right generator size.

## Inputs

- **Refrigerator** — Running: 150W, Starting: 400W
- **Air Conditioner (window unit)** — Running: 1,500W, Starting: 2,200W
- **Sump Pump** — Running: 800W, Starting: 1,300W
- **Number of Light Bulbs** — min 0, max 50 — 60W-equivalent LED bulbs (~10W each running)
- **Television** — Running: 200W, Starting: 200W (no motor surge)
- **Microwave** — Running: 1,000W, Starting: 1,500W
- **Computer / Laptop** — Running: 200W, Starting: 200W

## Outputs

- **Running Watts** — Total continuous power draw of selected appliances
- **Starting Watts** — Peak power needed when motor-driven appliances start up
- **Recommended Generator** — formatted as text — Suggested generator size with headroom

## Details

Generators must handle two loads: running watts (the continuous power draw of all appliances) and starting watts (the momentary surge when motor-driven appliances like refrigerators and AC units start up). Starting watts can be 1.5-3x the running watts for appliances with motors.

The calculator adds a 20% safety margin above the peak wattage to prevent overloading. Running a generator at full capacity constantly reduces its lifespan and efficiency. A comfortable operating range is 50-75% of the generator's rated capacity.

For sensitive electronics (computers, TVs), an inverter generator is recommended as it produces cleaner power with less harmonic distortion. Conventional generators are fine for resistive loads like heaters and lights.

## Frequently Asked Questions

**Q: What is the difference between running and starting watts?**

A: Running watts is the continuous power an appliance uses. Starting watts is the brief surge of power needed when a motor starts (like a refrigerator compressor kicking on). Starting watts can be 1.5-3x the running watts but only last a few seconds.

**Q: Can I run everything at once?**

A: The calculator assumes worst-case with everything running simultaneously. In practice, you can manage loads by staggering when you turn on motor-driven appliances. Start the largest load first, let it stabilize, then add others.

**Q: Do I need an inverter generator?**

A: An inverter generator produces clean, stable power suitable for sensitive electronics. If you are powering computers, TVs, or medical devices, choose an inverter generator. For tools, pumps, and lights only, a conventional generator works fine.

**Q: How much fuel does a generator use?**

A: At 50% load, a typical portable generator uses about 0.5-1 gallon per hour for a 3,500W unit. Larger generators use more. Propane generators are cleaner but produce slightly less power per gallon equivalent.

**Q: Can I connect a generator to my house wiring?**

A: You must use a transfer switch installed by a licensed electrician. Never plug a generator directly into a wall outlet (backfeeding), as this is extremely dangerous and can electrocute utility workers and damage your home's electrical system.

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Source: https://vastcalc.com/calculators/everyday/generator-wattage
Category: Everyday Life
Last updated: 2026-04-21