Trip Computer- MPG Estimate vs. Actual

davidyan

So I was bored and decided to create a spreadsheet to track the MPG I get everytime after fill up. Driving 333.3 miles since the last FULL fill up, I used 15.371 gallons equating to 21.7 MPG.

My trip computer read out an average of 21.1 MPG. I made sure it was reset immediately after I filled up last. This is a difference of about 3% between the computer reading and my actual calc. Does anyone think that this is significant?

Couple plausible explanations for the difference:

- The car's computer calculated that I used more than 15.371 gallons as per the gas station meter. If this is the case, I'll make sure to continue buying gas from that station at that pump...
- The gas pump could have stopped a little short of a full fillup.
- My previous tank could have been slightly overfilled and not again this time.

Its unlikely that the an inaccuracy in the odometer reading of 333.3 miles could be the culprit since the car's trip computer probably uses the same readout for its calculation, or something mathematically tied to it like avg. speed.

Sorry for the otherwise random post but I thought I'd share and will continue to track until I get tired of it.