Generator guides and free calculators

Size, run and troubleshoot your generator with confidence

Free calculators that show their formulas, plain-English guides and safety-first advice for homeowners, RV owners and small businesses.

Use the free calculators Fix a generator problem
  • Formulas explained
  • Worked examples
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Portable generator powering a modern home during an evening power outage

Free generator and electricity calculators

Every calculator shows its formula and a worked example, so you can check the numbers yourself.

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Generator Load CalculatorChoose common U.S. appliances or add your own loads to estimate running watts, startup surge, and generator demand.Open calculator Generator Size CalculatorEstimate generator capacity from running load, additional startup surge, and a capacity margin.Open calculator Generator Runtime CalculatorEstimate how many hours a generator runs on the fuel you have, from tank size and fuel use per hour.Open calculator Generator Fuel Consumption CalculatorEstimate gallons (or cubic feet) per hour and running cost for gasoline, propane, natural gas and diesel generators.Open calculator Generator Cost CalculatorTotal cost of owning a generator per year, per running hour and per kWh, including fuel and maintenance.Open calculator Watts to Amps CalculatorConvert watts to amps (and amps to watts) for DC, single-phase and three-phase circuits.Open calculator

Plan your backup power in three steps

Work from what you need to run to what it will cost, in this order.

Add up your load

List the appliances you want to run and total their running watts and starting surge.

Generator Load Calculator →

Choose the right size

Turn your load into a minimum generator rating with a sensible reserve for starting loads.

Generator Size Calculator →

Plan fuel and runtime

Estimate fuel per hour, how long a tank lasts and what an outage will cost to run.

Fuel Consumption Calculator →

Browse by topic

From choosing a generator to keeping it running for years.

Generator TypesHow portable, inverter, standby, dual fuel, propane, gasoline and solar generators work, and which type suits homes, RVs,…22 guides Sizing & PowerWork out how many watts you need, understand running and starting watts, and safely power appliances, computers and…5 guides Fuel & RuntimeHow much fuel generators use, how long they run per tank, and how to estimate runtime and running…4 guides Installation & SafetyTransfer switches, interlocks, grounding, placement and carbon monoxide safety: how to connect and run a generator without putting…7 guides MaintenanceOil changes, storage, lifespan and routine care to keep your generator starting reliably and running for years.3 guides TroubleshootingStep-by-step fixes for generators that will not start, surge, shut off, trip breakers or run with no power,…6 guides Brands & ModelsSpecifications, features and practical notes on generator brands and individual models, including Honda, Champion, Predator, Generac and Westinghouse.20 guides

Generator won’t cooperate?

Step-by-step fixes for the most common generator problems, with quick diagnosis tables.

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Latest guides

Sizing, fuel, runtime, installation and maintenance explained in plain English.

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Inverter Generators

Best Inverter Generators: Compared by Use

An inverter generator produces power that is cleaner and steadier than a conventional open-frame unit, and most are quieter and lighter for their output.…

Generator safety basics

Every year people are hurt by generators used indoors or connected the wrong way. These three rules prevent most of it.

Read the safety guide
  • Run it outdoors, away from the house. Carbon monoxide from the exhaust can be fatal within minutes. Keep the generator at least 20 feet from doors, windows and vents.
  • Never backfeed through a wall outlet. Use a transfer switch or interlock installed by a licensed electrician. See safe ways to connect a generator to a house.
  • Install battery-powered CO alarms on every level of your home and test them regularly.

How we write our guides

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Formulas, not guesses

Every calculator shows the math and a worked example, so you can verify any result by hand.

Sources you can check

Figures are based on manufacturer specifications, published fuel data and electrical codes, and we say when something is an estimate.

Independent advice

No manufacturer or retailer pays for rankings, reviews or recommendations on this site.