Semi truck MPG calculator: loaded vs empty

This semi truck MPG calculator returns your loaded and empty fuel economy, the percentage drop when loaded, and fuel cost per mile for each.

Fuel is the largest variable cost for most trucks, and miles per gallon decides how big it is. The catch is that MPG is not one number. The same truck gets very different fuel economy loaded at 75,000 pounds than it does deadheading empty, and a single average can make some loads look better than they are.

How it works

Enter two fill-ups: one where the truck ran loaded and one where it ran empty or light. For each, the calculator divides miles driven since the last full fill-up by the gallons it took to refill.

• MPG = miles since last fill-up / gallons to fill
• Fuel cost per mile = diesel price / MPG
• Loaded drop = 1 - (loaded MPG / empty MPG)

Switch Units to see liters per 100 kilometers, the usual measure outside the US. Lower is better there.

A worked example

A truck runs 620 miles loaded at 72,000 pounds gross and takes 102 gallons to fill: about 6.1 MPG. Later it runs 540 miles empty and takes 74 gallons: about 7.3 MPG. Loaded fuel economy is about 17% lower. At $3.90 a gallon, fuel costs about 64 cents per mile loaded and about 53 cents empty.

That difference matters when you judge a load. If you plan a heavy load using your empty MPG, you will underestimate fuel by more than ten cents a mile.

What affects semi truck miles per gallon

• Weight. Heavier loads cost more fuel, especially on grades and in stop-and-go traffic. Our guide on how much a semi truck weighs covers empty weights and legal limits.
• Speed. Aerodynamic drag rises quickly with speed. A few miles per hour slower often saves real fuel on long runs.
• Aerodynamics. Trailer skirts, gap reducers and a clean roof line help at highway speed. Flatbeds and car haulers face more drag from the load itself.
• Terrain and weather. Mountains, headwinds, cold weather and winter blend fuel lower MPG.
• Idling. Idle time burns fuel without adding miles, which drags down the tank average.
• Tires and maintenance. Low tire pressure, dragging brakes and a dirty air filter all cost fuel.
• Driving habits. Smooth acceleration, progressive shifting and coasting into stops make a measurable difference.

Getting an accurate number

Fill the tanks to the same point each time, ideally at the same pump. Record miles and gallons from the receipt, not from memory. One tank can be off by several gallons, so average three or more fill-ups before drawing conclusions. If you run dual tanks, fill both.

Knowing your tank size helps you plan fuel stops on long runs; our guide to the semi truck fuel tank covers common capacities and how to check yours.

Using your MPG

Once you know loaded and empty MPG, plug them into the trip fuel cost calculator to price a specific trip. If you are on the shipper or broker side of a fuel surcharge, or want to check one, the fuel surcharge calculator shows how a surcharge is built from a base price and MPG.

Best miles per gallon truck habits

The trucks that post the best numbers are rarely magic. Their owners keep tires at the right pressure, hold a steady highway speed, keep idle time low and spec the truck for the work it does. Small changes add up: a couple of miles per hour off the cruise setting, a lighter right foot on the climbs and less time idling at the dock can each move the tank average. Track one change at a time over several fill-ups, so you know which ones pay off on your truck and your lanes.

What the results mean

If your loaded drop is far bigger than you expect, look at what changed between the two tanks: terrain, weather, speed or idle time. If both numbers drop over a few months, check tire pressure, alignment, brakes and the air filter, and look at fault codes. A sudden fall in MPG is often an early sign of a mechanical problem.

Where we fit

Our desk prices every load with your real fuel cost, not a guess. We find and negotiate the load, you say yes, counter or no, and the broker sends the rate confirmation to you to sign. Our page for owner-operators explains how it works for single trucks.