Computing gas mileage

[DesmoDiva]

This is how I'm calculating the gas mileage in my car.  

Someone's trying to tell me I'm doing it all wrong.  

Last fill up mileage: A
Mileage this fill up: B
# of gallons of gas pumped in: X

B-A = miles/gal
X

Here's the twist; I don't always fill the tank.  I don't think it matters, B says it definitely does.

What do you think??

[He Man]

it only matters if you dont consistently fill her up to the same point in the tank.

[Popeye the Sailor]

It does matter.


Take your example.

Start at 0 miles, drive 300.

Stop for gas, and put in one gallon.

(300-0)/1= 300 miles/gallon.

[erkishhorde]

That's how I calculate my mileage but I fill until the pump stops. Assuming that every pump stops at the same "full" level, I feel that I get an accurate estimate of my mileage. Assuming that you top off to the nearest $.10 or something like that, the formula will not give you "accurate" results. You need to put in a full tank in order to calculate how much gas was actually used for the distance covered. Otherwise you're overestimating your mileage, as given my Mr. I's example.

[Latinbalar]

No you have it right no matter how you figure it.  You only fill up what you drove.  So what you put in the tank represents what you used. So that number will tell you how much you used previously.

[He Man]

So what you put in the tank represents what you used.

Only if you fill up to the point where you stopped last time. The logical place would be when the pump automatically stops.

[Popeye the Sailor]

Trust me.


I'm an engineer. 

[Speeddog]

The OP's formula will work, given the following:

Gas tank was full at mileage A.

Gas tank is full at mileage B.

X, the total amount of gas, is the *total* amount pumped in between mileage A and mileage B.

-------------------------
If you partially fill between mileage A and the fill-up at mileage B, then you've got to add that to the fill-up at mileage B to get a correct value for X.

[Popeye the Sailor]

I can sell you some magnets to put on the fuel line-they align your hydrocarbons and make you get way more better mileage. 

[Randimus Maximus]

don't for get that tornado thingamajig that swirls the air in the intake.

[Rev. Millertime]

[/quote]

don't for get that tornado thingamajig that swirls the air in the intake.

So much for my sales pitch... thanks Randy! 

[Speeddog]

There's no conveyor belt involved here, right?

[Popeye the Sailor]

There's no conveyor belt involved here, right?

It doesn't matter-the car won't take off.

[Randimus Maximus]

must be the meds, not sure why I spelled "forget" as "for get". 

[Goat_Herder]

The better way to do this:

Gas tank was full at mileage A.
Ride till you have 5 or 10 fill ups
Gas tank is full at mileage B.

(B - A) / total gas = better average

This way, you get a better measurement of gas consumed and therefore more accurate MPG.