Fuel Cost Calculator
Trip fuel cost from miles, MPG, and pump price — plus your fuel cost per mile and what an MPG bump is actually worth.
Enter your run and hit PUMP THE NUMBERS
How this calculator works
Three inputs, three answers. The calculator divides your trip miles by your real-world MPG to get gallons burned, multiplies gallons by the pump price for the trip cost, and divides price by MPG for the number worth memorizing: your fuel cost per mile. Add your monthly miles and it also projects your monthly diesel spend — and prices out exactly what half an MPG is worth on your miles, not a fleet brochure's.
trip cost = gallons × price per gallon
fuel cost per mile = price ÷ MPG
Use your actual loaded average for MPG — the number your ELD or a few fill-ups tell you, not what the truck did empty across Kansas with a tailwind. Fuel is typically a quarter to a third of every operating dollar, so this per-mile figure feeds straight into your cost per mile and every rate decision built on it.
Two worked examples
Example 1 — pricing a 1,000-mile run
Chicago to Laredo is right around 1,000 miles. At 6.5 MPG the truck drinks about 154 gallons, and at $3.85 a gallon that's $592 in diesel — $0.59 for every mile. Now that load offer has context: a $2.00/mile rate has 59 cents spoken for at the pump before the truck payment, insurance, or you see anything. If the broker adds 150 deadhead miles to reach the pickup, tack on another $89 of fuel nobody's paying for.
Example 2 — what slowing down is worth
Same truck, 10,000 miles a month, but it's been averaging 6.0 MPG at 68 mph on cruise. That's $6,417 a month in fuel. Backing the cruise down to about 63 and staying out of the throttle gets it to 6.5 — worth roughly 128 gallons, or $494 a month, $5,900 a year. Nothing was bought, nothing was installed; the load just gets there forty minutes later. Very few things in trucking pay $490 a month for showing up slightly less early.
From the road
The sign price is bait. What matters is your out-the-door number: a fuel card discount of 25 to 75 cents can make the expensive-looking stop the cheapest one on the exit, and the discounts reshuffle daily. Check the card app before you commit the tanks, and if you're running your own authority, learn the IFTA wrinkle — fuel tax settles by the miles you run in each state, not where you bought, so the sharp comparison across a state line is the price net of that state's tax. Sometimes the "cheap" side of the line isn't.
The other leak is the one you can hear. An overnight idle burns around eight gallons — call it $30 a night, $200-plus a week in the seasons when everybody idles. An APU pays itself off quietly, a bunk heater faster than that. And the boring stuff is real: soft drive tires drag MPG down tenths at a time, a roof fairing set wrong for the trailer gap costs you at 65 mph, and winter fronts help more than louvers in real cold. None of it is exciting. Neither is $6,000 a year, until it's in your account instead of the tank.
FAQ
How do I figure fuel cost for a trip?
Miles ÷ MPG = gallons, gallons × price = cost. 1,000 miles at 6.5 MPG is ~154 gallons; at $3.85 that's ~$592.
What MPG should a semi get?
Most loaded Class 8 trucks run 5.5–7.5 MPG. Speed is the big one — backing off from 70 to 62 mph can be worth over half an MPG. Weight, terrain, and trailer gap do the rest.
Is half an MPG really worth chasing?
At 10,000 miles/month and $3.85 diesel, 6.0 → 6.5 MPG saves ~$494 a month. That's a truck payment every five months.
How much fuel does idling burn?
Figure ~0.8 gallons an hour. A 10-hour break on the main engine is about 8 gallons — $30 a night, $200+ a week if it's every break. That's the math that buys an APU or a bunk heater.
Should I just fuel at the cheapest pump price?
Compare your out-the-door price, not the sign — card discounts move stops from priciest to cheapest overnight. And under IFTA, tax settles by where you drive, not where you buy, so across state lines compare prices net of tax.