A change in diesel price looks small when quoted per gallon. Multiply it by monthly fuel use and it becomes a number you can put next to the operating budget. Start with the gallons consumed, or estimate them from the miles driven and measured fuel economy.
Build a budget from distance
Suppose ten trucks travel 6,500 miles each in a month and average 6.5 miles per U.S. gallon. The fleet drives 65,000 miles and uses 10,000 gallons. At $4.50 per gallon, monthly fuel costs $45,000, roughly $0.69 per mile. A price rise to $5.00 brings the estimate to $50,000.
Separate price from fuel use
The $5,000 difference assumes the same routes, distance and fuel economy. If the trucks run more miles or spend more time idling, update the gallons as well. For mixed fleets, calculate each group separately and add the results. This keeps a long-haul group from masking the fuel use of trucks running shorter city routes.
Choose a price that fits your operation
A national weekly retail average is a benchmark. Your invoice can reflect a regional market, fuel-card discounts and taxes. Use the price you expect to pay, then test a higher and a lower case. Keep the benchmark date with your notes so a colleague can repeat the estimate.
Repeat this example in the Fleet Fuel Cost Calculator or try the price slider on the Fuel Budget Simulator. See the EIA weekly on-highway diesel series for the U.S. retail benchmark.