What Is a Good MPG for a Semi Truck — and What Does Half an MPG Cost You?

By Erkan Ozturk — owner-operator, HAWD Trucking LLC (USDOT 4436030), Chattanooga TN · Last updated July 11, 2026

What MPG does a semi truck actually get?

There is no single answer, but there are honest landmarks. NACFE’s Fleet Fuel Study — the running record of what real North American fleets achieve — put efficiency-focused fleets at a 7.77 MPG average in 2023, while the broader national average sits nearer 6.9 MPG. The best-run trucks clear 8; older equipment hauling heavy over mountains in the cold can live below 6.

The spread is that wide because MPG is the sum of a dozen things you half-control: engine and gearing, gross weight, terrain, speed, wind, tire choice and pressure, aerodynamics, and — often the biggest single lever — idle time. So the useful question is not “what’s the average” but “what’s mine, and what is each tenth of it worth?” That second question has a clean formula.

Why does MPG matter so much to your cost per mile?

Because fuel is usually the single largest variable cost a mile creates, and its price per mile falls straight out of your MPG:

fuelCostPerMile = dieselPrice ÷ MPG

One division, and it’s unforgiving in the middle of the range. The move from 6.0 to 6.5 MPG saves more per mile than the move from 8.0 to 8.5, because you’re dividing a fixed diesel price by a smaller number down low. Here is the whole curve at today’s national diesel average:

From the bottom of that table to the top is a swing of about 22 cents on every mile — the difference between an aging, heavy, high-idle operation and a dialed-in one. Fuel cost per mile is one line of your full cost stack; the mechanics of the fuel line, including surcharges and pump-price swings, get their own page: how do I calculate fuel cost per mile for a truck?

What does half an MPG actually add up to over a year?

Half an MPG sounds like a rounding error until you multiply it by a year of miles. Take the per-mile savings from the table above and run them across 90,000 miles — a common owner-operator year — and the numbers stop looking small:

Roughly $4,500 a year for finding half a mile per gallon — held speed, less idling, correct tire pressure, trimmed deadhead. That’s not a fuel-card gimmick; it’s the same math the brochure MPG hides. And it compounds with diesel: the higher the price at the pump, the more each tenth of an MPG is worth, which is exactly why a live diesel number beats a stale one. Fuel surcharges are meant to offset part of that price swing — how does a fuel surcharge work? walks through when they actually cover you.

Do semis get better MPG loaded or empty?

Empty, and it’s intuitive once you think in terms of energy: a lighter truck takes less work to get moving and less to hold at speed, so a deadhead leg usually posts a higher MPG than the same lane loaded to 80,000 pounds. The gap is real but modest — a well-loaded aerodynamic truck doesn’t collapse to half its empty mileage, because a large share of highway fuel goes to pushing air, not weight.

The trap is reading “better MPG” as “cheaper.” Those empty miles still burn diesel, still wear tires and brakes, and earn nothing while they do it. That’s why deadhead is counted as a cost of the load that caused it rather than a free repositioning bonus — the full accounting is in what does deadhead really cost per mile? A higher empty MPG softens the blow of a deadhead leg; it never erases it.

Why use your own MPG instead of the average?

Because the average describes the industry, not your truck. Two owner-operators pulling the same lane at 6.5 and 7.5 MPG are running fuel costs about 9 cents a mile apart — over $8,000 a year at 90,000 miles — while a fleet average of 6.9 tells neither of them the truth about their own week. Fuel cost per mile is the biggest movable line in your cost per mile, so plugging in a brochure number quietly mis-prices every load you evaluate.

The cleanest way to measure it is the honest one: miles driven divided by gallons burned across several fill-ups from your own receipts, tracked across seasons so winter blends and headwinds land in the average instead of hiding from it. That real MPG then flows into the rest of the cost stack — see how do I calculate cost per mile for a semi truck? for how fuel sits alongside fixed and variable costs. LoadWizz uses your truck’s real MPG — not a fleet average — every time it prices fuel on a load. The math itself needs nothing but your odometer and your fuel receipts; more of it lives in the Learn library.