When purchasing a trailer or tow vehicle, or budgeting for a trip, it would be nice to know approximately what kind of mileage you might expect. However, this information is tough to find, probably because it varies so much from vehicle to vehicle, size of trailer, where you are driving, style of driving, and number of passengers.

Using a couple data points, some rules on thumb, and reports from travel trailer owners, here’s a quick calculation that is likely to be accurate within 15%.

Your average miles per gallon will decrease by about 50% of your town vehicle’s actual (not published) Highway MPG (not city) rating if (a) you drive at around 55-60 miles per hour using cruise control; and, (b) your trailer’s Gross Vehicle Weight Rating (GVWR) is between 50%-75% of your town vehicle’s towing capacity.

How We Calculated / Estimated This

Our current tow vehicle is a 2019 Ford Expedition XLT with heavy duty towing package, allowing for a towing capacity of 9,300 pounds. While driving on the freeway using cruise control at around 65 miles per hour, we can expect mileage of about 21-22 MPG in the two-wheel drive setting. (This is lower than the published expected 24 MPG on the Ford Website.)

Our travel trailer is a 2020 Lance 2185 with a dry weight of 4,565 pounds and cargo weight of 1,425 pounds, for a gross vehicle weight rating (GVWR) of 6,000 pounds. I estimate it’s loaded at about 50% of possible capacity (we don’t usually fill the fresh water track while traveling), for a typical weight of about 5,250 pounds. However, my experience is that 90% of people load their trailers largely about the same, so it’s easiest to just use GVWR for this measurement, since this is a well-known and published statistic.

On a recent three-week trip from California through Nevada, Utah and Colorado, we traveled 2,551 miles in 65 hours and 15 minutes of travel time, averaging about 39 miles per hour. The Ford Expedition recorded an average of 10.9 miles per gallon.

However, I estimate that we took eight short trips (under 20 miles), and one long trip (40 miles) in the vehicle without the Lance travel trailer. Adjusting for these trips, I estimate our average was 10.5 miles per gallon, or about 50% of our highway average using cruise control when not pulling the Lance 2185.

Our previous trailer was a 2016 Forest River RPod (With a gross vehicle weight of 3,760 lbs), pulled by a 2017 Toyota Highlander XLE with towing package, allowing for a towing capacity of 5,000 pounds. In this scenario, we averaged 23.8 miles per gallon (highway) in cruise control at 65 miles per hour not towing, and 12.1 miles per gallon towing at 55-60 miles per hour.

I found several other metrics from reliable sources:

• For heavy trailer loads of 5,000 or more, subtract 25-35 percent mileage. (Source: ItStillRuns)
• A simple roof rack decreases fuel economy by 5%. (Source: Consumer Reports)
• Every 100 pounds (45 kilograms) of extra weight in your vehicle decreases fuel efficiency by 2 percent. (Source: US Department of Energy, fueleconomy.gov)
• You can assume that each 5 mph you drive over 50 mph is like paying an additional $0.18 per gallon for gas. (Source: US Department of Energy, fueleconomy.gov)

After considering these sources, and talking with other people pulling travel trailers ranging from 16 feet to 32 feet, I find that this is a reusable rule of thumb. While actual mileage can vary by about 10%-15%, I find that using the tow vehicle’s (actual, not rated) higher highway MPG rating (rather than city MPG), you can consistently expect about 50% of this value for your actual miles per gallon while towing.