Generator & Electricity Calculators

Free, easy-to-use calculators for planning backup power. Size a generator, estimate fuel and runtime, work out costs and convert common electrical units. Every tool shows its formula and a worked example so you can check the numbers yourself.

Generator Calculators

Generator Load Calculator Choose common U.S. appliances or add your own loads to estimate running watts, startup surge, and generator demand. Generator Size Calculator Estimate generator capacity from running load, additional startup surge, and a capacity margin. Generator Runtime Calculator Estimate how many hours a generator runs on the fuel you have, from tank size and fuel use per hour. Generator Fuel Consumption Calculator Estimate gallons (or cubic feet) per hour and running cost for gasoline, propane, natural gas and diesel generators. Generator Cost Calculator Total cost of owning a generator per year, per running hour and per kWh, including fuel and maintenance. Appliance Wattage Chart Running and starting watts for 120+ common household, RV, workshop and business appliances. Battery Runtime Calculator How long a battery bank or portable power station will run your devices, in Wh or Ah.

Electricity Calculators

Watts to Amps Calculator Convert watts to amps (and amps to watts) for DC, single-phase and three-phase circuits. kWh to Watts Calculator Convert energy in kWh to power in watts over a period of time, and back again. Electricity Cost Calculator What an appliance costs to run per day, month and year at your electricity rate. kVA to kW Calculator Convert apparent power (kVA) to real power (kW) with power factor, as used on generator nameplates. Wire Size & Voltage Drop Calculator Smallest copper or aluminum conductor for your current and run length, with voltage drop.

Where to start

  1. Add up your load with the Generator Load Calculator, or look up individual appliances in the wattage chart.
  2. Size the generator with the Generator Size Calculator so it covers both running and starting watts.
  3. Plan your fuel with the Fuel Consumption Calculator and the Runtime Calculator.
  4. Compare costs with the Generator Cost Calculator.
  5. Plan the connection with the Wire Size Calculator and our guide to connecting a generator safely.

All results are estimates for planning. Confirm with your equipment’s specifications and, for anything connected to your home’s wiring, a licensed electrician.