Semi truck fill-up cost calculator

How the calculator works

The math is simple, but it's easy to get wrong at the pump when you're tired. The calculator follows four steps.

1. Capacity. Tank size x number of tanks.
2. Fuel left. Capacity x the gauge level. Gauges aren't precise, so treat this as an estimate.
3. Gallons needed. Capacity minus fuel left.
4. Cost. Gallons needed x (diesel price minus any fuel card discount).

It also shows your range on full tanks (capacity x mpg) and what a completely full load of fuel would cost, which is useful when you plan a run through expensive states.

A worked example

A tractor has two 125-gallon tanks, and the gauge reads a quarter full. Diesel is $3.90 a gallon with no discount, and the truck averages 6.5 mpg.

What the result means

The fill-up cost tells you what this stop will cost, not what fuel costs your business. For that, track fuel per mile. Divide what you spend on diesel by the miles you drive, or use the semi truck MPG calculator to see your fuel economy and cost per mile over several fill-ups.

Range is the other useful number. If full tanks take you about 1,600 miles, you can plan to buy fuel where prices are lower instead of wherever the gauge happens to run low. Leave a healthy reserve: running a diesel engine out of fuel can mean a costly roadside call.

Ways to spend less at the pump

• Plan fuel stops. Diesel prices can differ a lot between states and between stops on the same highway. Fuel up before an expensive stretch, not in the middle of one.
• Use a fuel card. Many fuel cards offer discounts per gallon at partner stops. Enter your discount in the calculator to see what it saves per fill-up.
• Watch your speed. Fuel economy drops as speed rises. The speed limiter impact calculator shows what a few miles per hour cost over a week.
• Cut idling. Idling burns fuel without moving freight. Auxiliary power units and bunk heaters can cut the burn on long rests.
• Cut empty miles. Fuel burned driving empty earns nothing. Planning the next load before you deliver is one of the best fuel savers there is.

Fuel weighs something too

Diesel weighs roughly 7 lb a gallon, so 250 gallons adds about 1,750 lb to the truck. On a light load that doesn't matter. On a heavy one it can decide whether you scale legal. If you're close to 80,000 lb, fill only what you need to reach the next stop and check your axle weights with the truck weight limit checker. The tanks sit between the steer and drive axles, so the weight lands on both.

Checking diesel prices

Prices change every week and differ by region. The U.S. Energy Information Administration publishes weekly average diesel prices on its gasoline and diesel fuel update (checked October 2026), which is a good guide to the national and regional picture. For the price at a specific stop, check your fuel card app or the stop itself.

Fuel in the bigger picture

Fuel is one of the biggest costs of running a truck, which is why fuel prices move freight rates and fuel surcharges. Our guide to trucking industry statistics covers the numbers behind the industry, and the 18 wheeler guide shows where the tanks sit on a standard rig.

Fewer empty gallons

Every gallon burned on an empty mile is money spent with nothing coming back. Lining up the next load before the current one delivers is the cheapest fuel saving there is, and it's a habit on our desk. More on that in our page for owner-operators.