Skip to main content
Calcimator

Backup Generator Runtime Calculator

Estimate generator runtime based on fuel tank size, connected load, and fuel type. Calculate fuel consumption and operating costs.

Inputs

W
gal
W

Results

Estimated Runtime

15.1 hours

Fuel Consumption0.4 gal/hr
Load Percentage47%
Cost per Hour$1.39
Full Tank Cost$21.00
How to Use This Calculator
  1. Enter Generator Watts (the rated output on the nameplate) and Fuel Tank Gallons for your generator model.
  2. Select Fuel Type (propane, natural gas, or gasoline) as each has different energy density and consumption rates.
  3. Enter Connected Load Watts — the total wattage of appliances you plan to run during an outage.
  4. Review Runtime Hours to see how long your fuel supply will last at the specified load level.
  5. Check Load Percent to ensure the generator is loaded between 50–80% for efficient operation and longevity.
  6. Use Cost per Hour and Total Fuel Cost to plan outage budgets and compare generator options.

How the result changes with Fuel Tank Size

Fuel Tank SizeEstimated Runtime
51128.3 hours
176442.8 hours
325817.6 hours
4501,132.1 hours

What each input means

Generator Capacity
Rated running watts of your generator (not peak/surge watts).
Fuel Tank Size
Fuel tank capacity in gallons. Portable generators are typically 5-8 gal.
Connected Load
Total wattage of appliances and circuits connected to the generator.
Fuel Type
0 = Gasoline, 1 = Propane, 2 = Diesel.

What each result means

Estimated Runtime
Hours the generator can run on a full tank at the given load.
Fuel Consumption
Estimated fuel consumption rate adjusted for load percentage.
Load Percentage
Connected load as a percentage of generator capacity. Optimal is 50-75%.
Cost per Hour
Fuel cost per hour of operation at current load.
Full Tank Cost
Cost to fill the fuel tank at current average fuel prices.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Generator Capacity = 7500, Fuel Tank Size = 6, Connected Load = 3500, Fuel Type = 0 = 4 input(s) provided
  2. Calculate Estimated Runtime
    Estimated Runtime
    15.1 = 15.1
  3. Calculate Fuel Consumption
    Fuel Consumption
    0.4 = 0.4
  4. Calculate Load Percentage
    Load Percentage
    47 = 47%

Related Calculators

The questions that sit next to this one — chosen by subject, including calculators filed under a different category.

Home Automation & Smart Home

UPS Battery Sizing Calculator

Size an uninterruptible power supply for your home office. Calculate VA rating, battery capacity, and runtime for your equipment.

Home Automation & Smart Home

Whole-House Surge Protector Calculator

Size a whole-house surge protector for your electrical panel. Calculate kA rating, cost, and ROI based on your home and risk profile.

Military Planning

Fuel Consumption Calculator

Calculate fuel planning requirements from vehicle types, distance, terrain, and idle time for military logistics.

Emergency Management

Emergency Generator Fuel Calculator

Calculate fuel storage needs for emergency generator runtime based on generator size, load, fuel type, and duration.

Electrical Engineering

Emergency Generator Calculator

Size emergency generators with altitude and temperature derating, fuel consumption, and runtime estimates.

More in Home, Garden & Maintenance.