How do I know how much fuel I am really using?

Don't know how many vehicles you can add to that app but its several if you wanna keep up with mileage on your car, pickup, motorcycle, ect....

Here's another free, simple ap that I use every once in a while. It's a speedometer and its dead on accurate with my garmin. Useful to check accuracy of your vehicle speedometer. Once you open it, it takes a min or two to stabilize then its dead on.

 

Starting off with full tanks, I set the 'driver 2' odometer on the GPS to 0. When it gets up to about 950 miles I know I better put some fuel on. But what if I only go 500 miles and decide I need fuel? So at 500 miles and putting on 50 gallons times 6.5 MPG, so I take 500 minus 325 equals 175 is my new "0" on the driver 2 odometer, just can't go over 950 still. So I drive 650 more miles and put on 75 gallons set the odometer to 337 for new "0".