How Long Can A Generator Run On A Tank Of Gas?

How Long Can A Generator Run On A Tank Of Gas

A generator can be a real lifesaver in an emergency, but how long can a generator run on a tank of gas? Generator manufacturers typically list the expected runtime for a full tank of gas, but several factors can affect how long your generator runs. Taking a look at these factors and maximizing your generator’s gas tank will help you get the most out of your generator.

How Long Can A Generator Will Run On A Tank Of Gas?

The manufacturers of generators always indicate how long they expect to run on a full tank of gas. There are, however, some additional factors that can affect runtimes:

Cold Weather

Cold weather will cause most generators to use more fuel per hour than in normal conditions. The reduced efficiency means cranking up the generator’s engine speed to compensate, which uses even more gas. If you live in a cold area, it’s worth the time to experiment with running your generator on a full tank before an emergency strikes to find out how long it will last during colder months.

High Altitude

As elevation increases, air pressure drops. This means there is less oxygen available for the generator’s engine (the same principle applies when breathing at high altitudes). The reduced oxygen supply means more fuel must be burned per hour to maintain power output. Therefore generators run at lower efficiency and consume more fuel than they would at sea level. To compensate, some generators include or can be fitted with an exhaust gas recirculation loop that routes unburned gasses back into the air intake for burning (this also reduces exhaust emissions).

High Load

The more electricity a generator’s engine is asked to produce, the more fuel it must consume. If your home appliances are larger than average or you intend to use multiple devices at once (for example, running several power tools), expect to see lower runtimes. Most generators will show some drop in efficiency if they are pushed beyond their continuous load rating. Running air compressors and other high-load equipment can also pull too much amperage for your generator’s circuit breakers to handle, requiring them to be replaced with higher amperage units.

Low Fuel Level

The lowers the level in your generator’s tank when you try to restart it, the harder its engine must work to suck up gas from the tank. This strains the generator’s engine with little reward; running an almost empty tank dry will cause irreparable damage to most generators’ engines (you should always follow the manufacturer’s recommended low-fuel-level procedure). If you plan to store a generator long-term during a power outage, be sure to fill it with a stabilizer/conditioner like Sta-bill to prevent the fuel from degrading.

New vs. Old

Newer model generators are more efficient than older, less advanced models. They use less fuel per watt of power produced and produce cleaner emissions. These gains come at a cost, however; new generators tend to run on the more expensive side.

How To Calculate How Long Your Generator Will Run On A Tank Of Gas

In order to determine how long your generator will run on a full tank of gas, you need to know its wattage and the capacity of the fuel tank. The formula is:

$((tank size in gallons x estimated output watts) / 30)) = hours of runtime

If you have a 500-watt generator with a six-gallon tank, the formula works out to:

$((6 x 500)) / 30 = 4.2 hours of runtime

So a six-gallon tank should provide you with about four and a half hours of power. Remember that many factors can affect how long your generator will run on a full tank of gas. This will give you a close estimate of your generator’s runtime, but it may vary depending on the quality of gas and other conditions.

How To Maximize Your Generator’s Runtime On The Gas Tank?

You can get the most runtime from your generator by doing the following:

  • Maintain the engine properly by changing the oil regularly and making sure there is no debris in the air filter or carburetor. If your generator has a fuel filter make sure it is clean.
  • Keep the tank full of gasoline. A full tank won’t keep the engine running any longer than an empty one, but it will allow you to get the most runtime out of every drop. (Extend your generator’s life too!)
  • Make sure that all vents are free of debris, particularly around the fuel cap area.
  • Fill your generator with premium gasoline if at all possible. It’s a little more expensive, but it provides better performance and extends the life of your generator.

How To Get The Most Out Of Your Generator’s Gas Tank?

You can improve your generator’s run time by learning how to conserve its power

  1. Make sure your generator is in good working order because a faulty generator will use more fuel to do the same amount of work.
  2. Don’t overload your generator by running too many appliances at the same time or using a heavy load, such as an oven.
  3. Be careful with extension cords—if you can, plug appliances directly into your generator to access its full power.
  4. Use a DC to AC power inverter or an adapter so you can use small appliances that need to be plugged in.
  5. Consider using a gas stabilizer to reduce engine problems that can arise from old fuel.
  6. If you’re not going to use your generator for an extended period, store it in a cool, dry location.
  7. Keep an eye on your gas tank levels to make sure you’re never caught short-handed.

What Factors Can Affect How Long You Run A Generator?

When it comes to emergency power, generators are very useful. But you need to know how long it will run on a tank of gas before you can make an informed decision. Here are some factors that will affect how long a generator runs:


A generator only has a limited amount of power, so the more you ask it to do, the less time it will run.


Cold weather affects the power output of a generator in two ways: lower gas mileage and reduced engine power.

Fuel type

One gallon of propane can produce up to 91,500 BTUs. Approximately 124,000 BTUs can be generated by 1 gallon of gasoline. Considering that gasoline generators are the same energy efficient as propane generators, they will run 36% longer.

 Manufacturer’s specs

The manufacturer of your generator will provide an estimated runtime, which can vary depending on the load and environmental factors like temperature and fuel type.


Which Generators Are The Most Fuel-Efficient?

When it comes to generators, less fuel used means more money saved. Similar to how you don’t want a car that guzzles gas and spews out the exhaust, you probably don’t want a generator that demands premium fuel and leaves a trail of fumes behind. Therefore, we selected the least expensive models as our most fuel-efficient picks. Let’s take a look at the generators’ torque and wattage in order to understand how much power output you’ll have relative to consumption.
When looking for a generator, it is essential that you consider what appliances or tools will be running from it.
To find out which pieces of equipment can run off of your portable generator, check your owner’s manual or contact the manufacturer.

How To Store Gasoline For Your Generator?

Gasoline has a shelf life of just six to 12 months. Storing the fuel in an external container ensures that humidity doesn’t get into the container and create rust. Keep your generator equipment clean, too. Dusty equipment can cause problems with the fuel system and running the engine. In addition to keeping gas fresh, you’ll need a method of charging or powering your generator without draining its gasoline supply.

You should run your generator at least once a month for 10 minutes. Gasoline doesn’t evaporate when you don’t use it, but it can go stale. Keeping gasoline in your generator for longer than six months can cause problems. A stale tank of gas will make it hard for your generator to start the next time you need it.
You’ll also need to keep your generator clean if you want it to run correctly. Dusty equipment can prevent the motor from running correctly, so take some time to clean your generator between uses.

How Long Will A Generator Run On 5 Gallons Of Gas?

Your generator will run for at least 6 to 8 hours on 5 gallons of gas. Generally, the time depends on generator size, load on the generator, and fuel choice (gasoline vs. propane). 

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