Calculate fuel burned and idling costs per hour, day and year by vehicle type or engine size, using fuel price and idle time in liters or gallons.
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Idling Fuel Consumption Formula
The calculator estimates idle fuel use in liters per hour, then uses your idle time and fuel price to estimate cost.
By vehicle type
F = R
By engine size
F = D_L * k
Fuel cost
C_hr = F * P_L
C_day = C_hr * H
C_year = C_day * 365
Fuel_year = F * H * 365
- F = fuel burned while idling, in liters per hour
- R = typical idle fuel rate for the selected vehicle type, in liters per hour
- D_L = engine displacement in liters
- k = idle fuel factor, in liters per hour per liter of engine displacement
- P_L = fuel price per liter
- C_hr = cost per hour of idling
- C_day = cost per day of idling
- C_year = cost per year of idling
- H = hours idling per day
The vehicle mode uses a typical idle rate for the selected vehicle. The engine size mode converts displacement to liters, then multiplies by a gasoline or diesel factor. If you enter fuel price per gallon, the calculator converts it to price per liter before calculating cost.
Typical Idle Fuel Rates by Vehicle
| Vehicle type | Typical idle rate | Approx. US gal/hr |
|---|---|---|
| Compact car, gas, about 1.5 L | 0.4 L/hr | 0.11 gal/hr |
| Sedan or small SUV, gas, about 2.5 L | 0.6 L/hr | 0.16 gal/hr |
| Pickup or large SUV, gas, about 5 L | 0.9 L/hr | 0.24 gal/hr |
| Heavy-duty pickup, diesel | 1.5 L/hr | 0.40 gal/hr |
| School bus or delivery truck, diesel | 1.9 L/hr | 0.50 gal/hr |
| Semi-truck or Class 8, diesel | 3.0 L/hr | 0.79 gal/hr |
Engine Size Factors Used for Idle Estimates
| Fuel type | Factor | Meaning |
|---|---|---|
| Gasoline | 0.30 L/hr per engine liter | A 2.0 L gas engine idles at about 0.60 L/hr. |
| Diesel | 0.25 L/hr per engine liter | A 6.0 L diesel engine idles at about 1.50 L/hr. |
Example Calculations
Example 1: Sedan idling 1 hour per day
A sedan or small SUV uses about 0.6 L/hr while idling. If fuel costs $3.50 per gallon, the price per liter is $3.50 ÷ 3.785 = $0.9247/L.
Cost per hour = 0.6 × 0.9247 = $0.55. Cost per year = $0.55 × 1 × 365 = about $203.
Example 2: 6.0 L diesel engine idling 2 hours per day
Fuel per hour = 6.0 × 0.25 = 1.50 L/hr.
If diesel costs $1.40/L, cost per hour = 1.50 × 1.40 = $2.10. Cost per year = $2.10 × 2 × 365 = $1,533.
FAQ
How accurate is an idling fuel consumption estimate?
It is an estimate. Real idle fuel use depends on engine size, fuel type, engine temperature, accessories, air conditioning, electrical load, idle speed, and emissions equipment. The result is useful for planning fuel cost, but it may not match a measured fuel-flow reading exactly.
Does using air conditioning increase fuel burned while idling?
Yes. Air conditioning adds load to the engine. That can raise idle fuel consumption, especially in small gasoline vehicles. Heaters, defrosters, lights, PTO equipment, and high electrical loads can also increase idle fuel use.
How do I convert liters per hour to gallons per hour?
Divide liters per hour by 3.785. For example, 1.50 L/hr ÷ 3.785 = 0.40 US gal/hr.
