Why idling adds up
An idling engine burns fuel without moving a vehicle anywhere, and over months of daily idling (warming up a car, waiting in a work truck, or running a generator) that unproductive fuel use can become a real cost.
The formula
Total fuel used = Idle rate (gallons per hour) × Hours idling per day × Number of days. Total cost = Total fuel used × Fuel price. A heavy diesel truck typically idles at around 0.6 to 1 gallon per hour, while a passenger car idles at a much lower rate, so adjust the idle rate field to match your specific engine.
This is an estimate; actual idle fuel consumption varies by engine size, accessory load (like AC or a lift-gate), and ambient temperature.
Last reviewed August 2026