A Fuel Time Calculator is a planning and performance tool that estimates the total amount of time an engine can run on a specific amount of fuel. This is often referred to as the engine's "endurance" or "runtime." The calculator works by taking the total volume of fuel available and dividing it by the engine's fuel consumption rate (e.g., gallons per hour). This calculation is essential for a wide range of applications, from pilots calculating the flight endurance of an aircraft, to boat captains determining how long they can cruise, to homeowners figuring out how long their generator will run during a power outage. Consequently, it provides a critical piece of information for safety, planning, and operational efficiency.
formula of Fuel Time Calculator
The formulas for fuel time calculations are based on the relationship between fuel volume, consumption rate, and time.
1. Primary Formula: Calculating Total Runtime (Endurance)
This is the core formula to calculate how long an engine can run.
Formula:
Runtime = Total Fuel Amount / Fuel Consumption Rate
- Runtime: The total time the engine can operate (e.g., in hours).
- Total Fuel Amount: The total volume of fuel available (e.g., in gallons or liters).
- Fuel Consumption Rate: The rate at which the engine uses fuel (e.g., in gallons per hour or liters per hour).
2. Calculating the Fuel Consumption Rate
Often, the fuel consumption rate must be calculated first.
- Formula from Direct Measurement (for stationary engines):
Fuel Consumption Rate = Fuel Used / Time Period of Operation - Formula for Vehicles (from Speed and Efficiency):
This converts a vehicle's standard fuel efficiency (like MPG) into a consumption rate in gallons per hour (GPH).
Fuel Consumption Rate (GPH) = Average Speed (MPH) / Fuel Efficiency (MPG)
3. Calculating Travel Time for a Journey
This is an essential part of trip planning.
Formula:
Travel Time = Trip Distance / Average Speed
Estimated Generator Runtime
This table provides quick estimates for the runtime of a portable generator based on its fuel tank size and its fuel consumption at a typical 50% load.
| Generator Tank Size | Fuel Consumption at 50% Load | Estimated Runtime |
| 2 Gallons | 0.25 Gallons per Hour | ~8 hours |
| 4 Gallons | 0.40 Gallons per Hour | ~10 hours |
| 6 Gallons | 0.50 Gallons per Hour | ~12 hours |
| 8 Gallons | 0.65 Gallons per Hour | ~12.3 hours |
Example of Fuel Time Calculator
A boat owner is planning a trip and needs to know the maximum time they can run their main engine.
First, they gather the necessary information.
- Total Fuel Amount: The boat's fuel tank holds 100 gallons. They plan to keep a 10% reserve, so the usable fuel is 90 gallons.
- Fuel Consumption Rate: At their planned cruising speed, the boat's engine consumes 12 gallons per hour (GPH).
Next, they apply the primary runtime formula.
Runtime = Total Fuel Amount / Fuel Consumption Rate
Runtime = 90 gallons / 12 GPH = 7.5 hours
Therefore, the boat owner can run their engine for 7.5 hours at their planned cruising speed before reaching their 10% fuel reserve.
Most Common FAQs
Miles Per Gallon (MPG) is a measure of efficiency that is useful for vehicles traveling over a set distance. For engines that operate in a stationary position (like a generator) or where the primary concern is time (like a boat or an aircraft), the fuel consumption rate is more practically expressed as a volume per unit of time, such as Gallons Per Hour (GPH) or Liters Per Hour (LPH). This directly tells you how long your fuel supply will last.
The load on an engine has a major impact on its fuel consumption. An engine running under a heavy load (e.g., a generator powering many appliances, or a truck driving up a steep hill) will consume fuel at a much higher rate than an engine running under a light load. This is why generator manufacturers often provide fuel consumption rates at different load levels, such as 25%, 50%, and 100% load.
The most accurate way to determine your boat's GPH is through direct measurement. Start with a full tank of fuel and run the boat at a specific, constant RPM for a set amount of time (e.g., one hour). After the test, return to the dock and carefully measure the exact amount of fuel required to refill the tank. The number of gallons you add is your fuel consumption rate in GPH for that specific RPM.