How much does it cost to fill a semi truck?

This is the whole page. A car takes a dozen or so gallons; a semi's paired saddle tanks hold somewhere around 200 to 300 gallons, ten to twenty times as much, so the same act of filling up is a different order of transaction. At our defaults, topping two 120 gallon tanks from a tenth full is 216 gallons of diesel, and at $4.00 that is $864 before the DEF line. The reason this matters is not that the price per gallon is high, it is that the volume is large, and a large volume turns a per gallon price into the dominant term. A driver who spent years filling a car arrives with the intuition that the pump price is a minor detail, because on a car it is: a swing of thirty cents on twelve gallons is under four dollars. On 216 gallons the same swing is about $65, and it lands at every stop, which is how a habit that felt harmless on a car becomes the single biggest lever on a truck's running cost.

Because the price multiplies across hundreds of gallons, replacing our placeholder with the real number matters more here than on almost any other page on this site. Diesel is posted on a sign at the island you are pulling into, so the real number is right in front of you, and it moves with the day, the state, and whether you are on a fleet card or paying retail. If you run a fuel card with a negotiated discount or a per gallon rebate, the number that belongs in this calculator is your net cost per gallon, not the posted price, because the posted price is not what leaves your account. Where you buy also moves it: a truck stop on a major corridor, a small independent, and a cardlock fuel island are three different prices for the same fuel, and on a fill this size the gap between them is real money rather than a rounding detail.

The gallons you actually pump is the difference between full and whatever is already in the tanks, which is why this page asks how full you are rather than assuming zero. A driver who tops up at every stop pumps a small gap and pays a small amount often; a driver who runs a tank most of the way down pumps close to the whole capacity and pays a large amount less often. Over a week the fuel burned is the same either way, but the number on any single receipt is not, and this page prices a single stop. Running a diesel genuinely dry is a bad idea, because drawing the very bottom of the tank risks pulling sediment and air into the fuel system and can require priming it to restart, which is why a sensible reserve stays aboard and the honest fill level here is rarely a true zero. Set it to what you really pull in at, not to empty.

A modern diesel with emissions aftertreatment carries diesel exhaust fluid in its own tank, commonly around 13 gallons, and burns it at a small fraction of the diesel it uses, so it needs topping up far less often than it needs fuel. That is why the DEF default here is a modest partial top up and why zero is an ordinary answer at any given stop. It belongs on the ledger because it is a genuine cost and it is bought at the pump alongside the diesel, but it is a minor line next to the fuel, and buying it by the gallon at a highway pump costs more per gallon than buying it in bulk totes, so a fleet that plans ahead pays less for it than a driver who tops up on the road. The page keeps DEF on its own line rather than folding it into the diesel, so you can see the fuel cost cleanly and add the DEF only when you are actually buying it.

It is the gallons you pump times the diesel price on the sign, and both numbers are yours rather than a national figure, so this page multiplies them rather than printing an average. The gallons is the gap between full and however full the tanks already are, not the whole capacity, and the price is whatever the island is posting today at your net rate if you run a fuel card. At our defaults, topping two 120 gallon tanks from a tenth full is 216 gallons, which at $4.00 a gallon is $864 of diesel, and with a small DEF top up the stop comes to $882. Change the capacity to your truck's real spec and the price to the sign in front of you and the answer moves with them. The point the page is built to make is that on hundreds of gallons the per gallon price is the whole bill, not a detail, so it is the number worth getting exactly right.

It depends on the truck, because saddle tanks are ordered in a range of sizes rather than coming in one standard. A tractor usually carries two tanks, one on each side of the frame, and individual tanks commonly run somewhere from 100 to 150 gallons each, so a paired set lands somewhere around 200 to 300 gallons total. Our default of 240 gallons is two 120 gallon tanks, a middle of the range placeholder rather than a measured norm. The real number for your truck is on the fleet spec sheet and is often stamped on the tank itself, and it is worth reading off rather than guessing, because a day cab, a regional tractor and a long haul sleeper are frequently spec'd with different capacities. Put your truck's real total in the capacity field above and the fill is priced against the tanks you actually have.

DEF, diesel exhaust fluid, is on the ledger as its own line, and you control whether it is in the total by how many gallons you enter. It is a fluid that any modern diesel with emissions aftertreatment injects into the exhaust to cut nitrogen oxides, held in a separate tank that is commonly around 13 gallons with its own filler and its own price per gallon. The truck uses it at a small fraction of the diesel it burns, so it does not need filling at every fuel stop, which is why the page treats it as an occasional partial top up and why entering zero is perfectly normal. It costs less per gallon bought in bulk totes than bought by the gallon at a highway pump, so where you buy it matters. It is a genuine cost and it belongs on the bill, but it is a small one beside the diesel, and keeping it separate lets you see the fuel cost on its own.

Because the price multiplies across every gallon, and there are hundreds of them. On a car that takes twelve gallons, a thirty cent move in the pump price is under four dollars, small enough to ignore, which is the intuition most people carry to the pump. On a fill of 216 gallons the same thirty cent move is about $65, and unlike the car it lands at every single stop, week after week. That is why fuel is the running cost fleets negotiate hardest over and why a fuel card with even a modest per gallon discount is worth having: a few cents a gallon looks like nothing until you multiply it by the volume a truck actually burns. It is also why the diesel price is the one input on this page most worth replacing with the real number rather than leaving at our placeholder, since it moves the answer more than anything else here.