How do you measure your MPG?
 

I can drive from Ft. Carson Colorado to Ft. Riley, Kansas (475 miles) on a single tank with 1/8's tank left over from a 30 gallon tank and cruising around 55-60 mpg from Ft. Carson via hwy 24 to I-70 and cruising at 70 mpg. So how do I figure out my MPG? I know going from Ft. Carson to Denver airport and back, I only burn just under a quarter of a tank, max speed is 70. So what the equation that I need?
Note my truck is a 2006 F-250 with a 6.0 bulletproofed engine with a 5" lift. I'm not exactly how heavy she is, but I did add a tool box and filled up with tools, the weight and lift kit doesn't seem to effect the fuel economy I'm getting now, compared with the 2-1/2" lift and no tool box and no tools.

Let fuelly do the work for you. You need to either keep a record of your odometer reading, or use your trip reading so you know how many miles you travel. When you add a fuel up, take note of how many gallons you put in, once you've entered both the miles traveled and the fuel used, fuelly will calculate your economy.

That's a thirsty beast you have there, I get almost 800 miles on my little 11 gallon tank, but that's a small car V's a big truck ;)

Figuring fuel mileage is relatively easy, but it does require taking notes. To get started fill the tank and make a note of the odometer reading, or zero your trip meter if your truck has one. Next time you fill the tank, note the odometer reading and subtract the last reading to get the distance travelled (or use your trip meter's reading). Divide the number of gallons you just bought into the distance and behold! your miles per gallon. You might find it interesting to fill at Fort Carson, then again at Limon to get your mpg on US24. Repeat for the higher speed run on I70, which might give you an interesting insight on the fuel mileage penalty of higher speed. I'd want to do the same thing on the return trip, too. I suggest that, because in going from Limon to Ft Riley you descend from about 5400 feet to about 1100 feet, over 4000 feet "downhill". Returning, you climb back up, and climbing hills takes more fuel than going down.

By the way, if you want to know how much your truck weighs, most truck stops have certified scales and most will weigh the front axle, the rear axle, and the total. They will probably charge about $8. The first time I weighed a pickup I went to a scrap metal dealer and asked, and they weighed it for free. They usually weigh the truck with any scrap metal on board, unload the metal, then reweigh the empty truck to get the weight of the metal they are buying.

I can make the trip from Ft. Riley to Ft. Carson and use the same amount of fuel as going the other way. I know from looking up my records on my first truck (Chevy K2500) it weighed 8,600 lbs, I haven't weighed it since I had the engine rebuilt, bulletproofed and added the additional lift. I know the original weight is on my registration paperwork.

Yea she is a thirsty big beast, I'm trying to figure out if I do an engine swap with either the 7.3 or a Cat if I'll get more mpg compared to my 6.0

Tank full, odometer reading recorded, rinse and repeat. Number of gallons, subtract refill odometer reading from previous refill odometer reading. Keep a notebook or a piece of masking tape in the glove box with a pencil.

Thanks, I've been doing that, or I'll write my mileage on the receipt like my dad does, but I tend to forget... Hopefully the app will work and get it close

If your registration is like mine, it does not list the weight of the truck. It lists the maximum allowable weight, the GVWR. The Gross Vehicle Weight Rating minus the actual weight is the payload capacity. There should be a sticker inside the driver's door (usually) listing the maximum allowable weights for front and rear axles, and the GVWR which might be less than the sum of front and rear. The only way to know what it actually weighs is to weigh it. Personally, I weigh mine with full fuel and whatever I usually carry in it. Be aware that people are also part of the payload. If you happen to carry four 200 pound men in the truck, you have used 800 pounds of your payload.

Your idea is good......but might not offer the desired effect.

It appears you're working against the grain for mileage. Got a lift kit, and extra weight? Gee... just lifting it kills mileage.

Another way you can easily get weight. Haul something to the landfill. When you leave. They will give you the weight of your vehicle. You might be able to just see it for yourself.