How to calculate Fuel Economy

divide the number of miles by the number of gal.( 240 miles 6 gals. 40 miles per gal.)

 

let's make an example:
date 01/03/04 odo 0 miles 0 gas full
date 31/03/04 odo 320 miles 320 gas 12 MPG 27
date 30/04/04 odo 920 miles 600 gas 20 MPG 30

(number are fictious) odo is the total number of miles and gas is the gallons added at the date

 

Another example:

Figures below are made up by me...

When you bought your car, there were 5 miles on it and the tank was full (assuming the dealer did his job correctly). When your odo meter reaches 420 miles the last bar on the gas gauge (searching for the right word here?) is starting to blink so you fill her up. You put 10 gallons of gas into the tank. Now you can calculate the MPG:
You tanked 10 gallons and drove 415 miles (420 - 5). So to get the MPG you devide 415 by 10. Which would give you a MPG of 41.5.

The tank is full again. When next the little bar starts blinking the odo meter reads 910 miles. Once again you put some gas into the tank, 11 gallons this time.

You devide the number of miles you have driven since your last tankstop by the number of gallons you just paid for: (910 - 420) / 11, makes 490 / 11 = 44.5

Easiest thing is to use a spreadsheet to keep track of these things. Maybe you can find one on the website of John1701. http://john1701a.com/

 

From another PriusChat thread (the Average Miles per Tank topic), it sounded to me as if the calculated MPG on the fuel consumption screen of your Prius could be different than the calculations you take and calculate manually.

Would others agree with that?

At any rate, I certainly plan to keep track of the milelage manually -- just to check. These would be the "real" figures in any case.

 

One other thing that I haven't seen any discussion on about mileage calculation is the fact that its the amount of miles you get for the gas burned not the amount you put back in the tank. With the bladder system used in the prius I seem to remember that the tank capacity can vary which will affect your calculations on any individual fillup though over time if one totals the miles and totals the gallons of gas before figuring the miles per gallon, this should even out.

Jon

 

The key to getting a true MPG read on a car is to do it over a number of consecutive tanks, preferably over similar operating conditions. With a more primitive vehicle, I always recommended a minimum of three tanks. Each time you gas up, the respective pump's automated shutoff coupled with the pitch of the gas station's surface can alter your calculation appreciably. When you start dividing 1,500 miles by 31.5 gallons, the little stuff falls away.

(Note: WHY are gas stations allowed to have anything but relatively flat surfaces? A good number are so bad you don't dare to check your oil level. Or, worse yet, as you level your "tooped off" vehicle, you can get gas spilling from your cap.)

 

Ok, just got my car yesterday and drove back 1300 fun filled miles from WY to IL (dont ask). With 5 stops for gas, I used 27.08 gallons total which gives me a nice round figure of 48MPG.
I started yesterday at 4pm and arrived at 8pm. Am going to bed. (but my garage has a new occupant. :mrgreen: )