Comparing a fuel-powered generator against a battery backup for an outage? See the Battery Backup Calculator.
Your Recent & Past Results
Restored a past calculation.
Compare Calculations
Side-by-Side Comparison
A comparison of your calculations' results.
Downloads
Includes your inputs and results for this calculation, plus any additional calculations you've compared.
Share & Print
The link includes your inputs and results, so anyone who opens it sees this exact calculation.
Disclaimer
This calculator provides estimates for informational purposes only. Always follow manufacturer instructions and local building or electrical codes, and consult a licensed contractor or electrician before acting on this information -- especially for structural work, electrical wiring, or fuel-burning equipment.
Estimating Runtime and Fuel Needs From Tank Capacity and Consumption Rate
A generator’s runtime on a full tank is its fuel tank capacity divided by its fuel consumption
rate at your typical load. Enter your tank’s capacity and the consumption rate from your
generator’s spec sheet (usually listed in gallons per hour at 50% and 100% load), and this
calculator estimates how long a full tank lasts. Add a target outage duration in the optional
section to see the total fuel — and number of tank refills — that outage would need.
A generator burns fuel faster at a heavier load, so use whichever consumption figure is closest to
what you actually plan to run.
Key Factors to Consider
Consumption rate varies with actual load, not just the generator’s rated capacity. A
generator running well below its maximum rated wattage typically burns noticeably less fuel per
hour than one running near full load — use the consumption figure closest to what you’re
actually powering, not the highest number on the spec sheet, for a more accurate runtime
estimate.
Planning fuel storage around a worst-case outage length means balancing two risks. Storing
too little risks running out mid-outage; storing more than local regulations allow, or more than
can be safely stored in approved containers, creates its own hazard. Check your local rules on
maximum safely storable fuel quantities before planning a large reserve.
Stored gasoline degrades over time. Fuel kept for an extended period (many months) can
degrade and cause starting or running problems later — a fuel stabilizer additive, used according
to its own instructions, is a common way to extend gasoline’s safe storage life if you’re keeping
a fuel reserve on hand for occasional outages rather than using it up regularly.
Useful to Know
Never refuel a generator while it’s running or still hot. Spilled fuel contacting a hot engine
or muffler is a real fire risk — always shut the generator off and let it cool for several minutes
before refueling, even mid-outage when it’s tempting to top off quickly and keep it running.
For a target outage duration, total fuel needed is the consumption rate multiplied by the outage
hours, and the number of tank refills is that total divided by the tank capacity, rounded up.
Worked Example
A 5-gallon tank with a generator burning 0.75 gallons per hour:
Runtime on a full tank: 5÷0.75≈6.7 hours.
Running continuously for a full day would use 0.75×24=18 gallons.
For a 72-hour (3-day) outage: 0.75×72=54 gallons total, or
⌈54÷5⌉=11 tank refills.
Estimar el Tiempo de Funcionamiento y la Necesidad de Combustible a Partir de la Capacidad del Tanque y el Consumo
La autonomía de un generador con el tanque lleno es la capacidad del tanque de combustible dividida por la tasa de consumo de combustible a tu carga típica. Ingresa la capacidad de tu tanque y la tasa de consumo de la hoja de especificaciones de tu generador (generalmente listada en galones por hora al 50% y 100% de carga), y esta calculadora estima cuánto dura un tanque lleno. Agrega una duración de apagón objetivo en la sección opcional para ver el combustible total — y el número de recargas de tanque — que ese apagón necesitaría.
Un generador quema combustible más rápido a una carga más pesada, así que usa la cifra de consumo más cercana a lo que realmente planeas operar.
Factores Clave a Considerar
La tasa de consumo varía según la carga real, no solo la capacidad nominal del generador. Un
generador que funciona muy por debajo de su vataje nominal máximo normalmente quema notablemente
menos combustible por hora que uno que funciona cerca de su carga completa — usa la cifra de
consumo más cercana a lo que realmente estás alimentando, no el número más alto de la hoja de
especificaciones, para una estimación de autonomía más precisa.
Planificar el almacenamiento de combustible según la duración de apagón del peor caso implica
equilibrar dos riesgos. Almacenar muy poco arriesga quedarse sin combustible a mitad del apagón;
almacenar más de lo que permiten las regulaciones locales, o más de lo que se puede almacenar de
forma segura en contenedores aprobados, crea su propio peligro. Verifica las reglas locales sobre
las cantidades máximas de combustible que se pueden almacenar de forma segura antes de planificar
una reserva grande.
La gasolina almacenada se degrada con el tiempo. El combustible guardado durante un período
prolongado (muchos meses) puede degradarse y causar problemas de arranque o funcionamiento más
adelante — un aditivo estabilizador de combustible, usado según sus propias instrucciones, es una
forma común de extender la vida útil segura de almacenamiento de la gasolina si mantienes una
reserva de combustible a mano para apagones ocasionales en lugar de usarla regularmente.
Útil Saber
Nunca reabastezcas un generador mientras está funcionando o todavía está caliente. El
combustible derramado en contacto con un motor o silenciador caliente es un riesgo real de incendio
— siempre apaga el generador y déjalo enfriar durante varios minutos antes de reabastecerlo, incluso
en medio de un apagón cuando es tentador llenarlo rápidamente y mantenerlo funcionando.
La Fórmula
Autonomıˊa (horas)=Tasa de Consumo de Combustible (gal/hr)Capacidad del Tanque (gal)
Para una duración de apagón objetivo, el combustible total necesario es la tasa de consumo multiplicada por las horas de apagón, y el número de recargas de tanque es ese total dividido por la capacidad del tanque, redondeado hacia arriba.
Ejemplo Resuelto
Un tanque de 5 galones con un generador que quema 0,75 galones por hora:
Autonomía con tanque lleno: 5÷0.75≈6.7 horas.
El funcionamiento continuo por un día completo usaría 0.75×24=18 galones.
Para un apagón de 72 horas (3 días): 0.75×72=54 galones en total, o
⌈54÷5⌉=11 recargas de tanque.
How is this different from the Generator Sizing Calculator?
Generator Sizing Calculator answers a POWER question -- what wattage generator you need to survive your appliances’ running load plus startup surge. This calculator answers a DURATION and FUEL question -- once you have a generator, how long it runs on a tank and how much fuel a multi-day outage will use.
Where do I find my generator’s fuel consumption rate?
“Gallons per hour” is a standard spec on a generator’s data plate or manual, usually listed at both 50% and 100% load -- use whichever is closer to your actual running load, since a generator burns noticeably more fuel at full load than at half load.
Should I plan fuel storage around the worst-case outage length?
It’s common to plan for a few days beyond your area’s typical outage length as a buffer, but always follow local regulations on how much fuel can be safely stored at home, and store it in approved containers away from the generator itself.
Is it safe to refuel a generator while it is running?
No -- never refuel a generator while it's running or still hot. Spilled fuel contacting a hot engine or muffler is a real fire risk. Always shut the generator off and let it cool for several minutes before refueling, even mid-outage.
Does stored gasoline go bad?
Yes -- gasoline stored for an extended period (many months) can degrade and cause starting or running problems later. A fuel stabilizer additive, used according to its own instructions, is a common way to extend safe storage life for fuel kept on hand for occasional outages.
Does this work for propane or natural gas generators too?
Yes -- the math is the same regardless of fuel type: divide tank or supply capacity by the consumption rate. Propane and natural gas generators have their own consumption rate (often listed in gallons or cubic feet per hour) on their spec sheet, so use that fuel's own rate rather than a gasoline generator's rate, since the two aren't interchangeable.
We use cookies for analytics and ads to help support this free site. You can accept all, or decline and we'll only use what's needed for the site to work.