calculated vs. computer MPG - Please post your results

317.8 miles
6.031 gal's
55.7 MPG Indicated
52.694 mpg Calculated

Reg gas with 10% Ethanol

95 % hwy driving / speed up to 75 mph

 

Well you guys peaked my interest so I decided to start keeping track of the difference. This is for the 2011 Prius

Miles = 379
Gallons=8.41
MPG displayed =48.1
Calculated 45.1
Tires =OEM 15" 40 front 38 Back
Shell regular with 10% ethanol
6.23% difference (ouch)
Most of my trips are no longer than 12 miles with two or three times per month having a 150 mile trip heavy traffic trip into Houston.

 

My last fill-up (2010 Prius)

530.6 miles using 8.958 gallons of gasoline

Calculated MPG = 59.2
Indicated MPG = 62.9
Difference = 3.7 mpg
% Difference = (62.9 - 59.2)/59.2 = 6.25%

 

50.8 displayed
48.9 actual
362 miles 7.41 gallons
Error 3.74%
Combined error last two fill ups 4.95%


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We have owned our '11 Prius III for six months and have just under 5K miles on it. We live near San Francisco CA where we have lots of traffic and mild weather. Our driving comprises 60% city and 40% highway. We regularly use CostCo regular gas. Our overall calculated gas mileage is 48.8 m/g. From my recollection that's 2-3 m/g less than what our Prius's computer has indicated. I will track the car's computed values in the future and report back when I have enough data.

I put 20% of those miles on our car and drive fairly economically, when I can. My wife put on the remaining 80% and is a more normal, less concerned driver.

Date of manufacture: 08/11

Update April 15, 2014: We have now owned our Prius for 3.5 years and love it more each day. We have just under 40K miles on it. It is still driven in the S.F. Bay area and uses CostCo regular gas. Our driving now comprises 40% city and 60% highway. My wife still puts on 80% of our car's mileage. Our overall gas mileage to date has averaged 52.4 and is still 2-3 m/g less than what our Prius's computer indicates.

 

only have the dealer fill up since I put my first tank fill a few days ago.

With 2 pips left
501 miles
9.041 to 1st click
car computer 52.7
calculated 55.41
Eco Mode- didn't know there was a "regular" mode
drove like normal car again since didn't know about other techniques
35 mph car computer avg.

I filled up with BP Non Ethonal 89 just to see if it made a difference. I doubt the Toyota dealership used Non Ethonal. I have no idea what my tires are or the pressure of them. I have driven the car mostly but my DH has also driven it. I don't want this tank to have his footprint on it so I can get a better idea of how my driving is. Employing some of the techniques offered here & now my mpg indicator is at 59.3mpg.

 

This is a very interesting post as one can see a significant improvement during one tank with the same driver just by employing gas saving techniques. Congatulations! :cheer2:

 

I think there will be variance with the results because of driving habits and situations. So I don't think that there will be an accurate standard for it. For the sake of trying to find it out, I will track my fill up and get the calculated results and post it too.

 

today driving around 60 miles round trip upped the trip computer to as high as 60.9 by the time I got home though it was back down to 60.1. Still really happy though- learning how to drive more "city" where there are multiple lights. The Hwy at 58-60 mph my mpg went down. Where I live more stop signs than any lights.

 

Have only had my 2012 Prius Two for two weeks. Driving in hilly terrain in Connecticut. My mileage (first calculation suspect due to the fact that I do not know how "full" the dealer filled the car before delivery):
FILL UP 1
MFD = 46.9
Calculated = 44.6
MFD vs. Calculated = -2.3
% Error = 5.16%

FILL UP 2
MFD = 52.4
Calculated = 50.0
MFD vs. Calculated = -2.4
% Error = 4.80%

 

What speeds ,type of driving(hwy/city) and tire pressure please im curious??

 

481 miles, last pip just started blinking
10.031 gallons

Calculated 47.95
Indicated 51.5
7.4%

almost all city miles

 

The comparison between calculated and computer MPG should be only modulated by the accuracy of gas pump and independent of car tires, driving habits/conditions, gas types... Costco gas pumps tend to inflate the gallon reading with which the company got class action lawsuit before.

 

Wow I think we need to get a life...

128 oz to a gal... yet your calculating your results using the first click of the pump as your top off point...Wow how many OZ in the average click? For what duration? and about a dozen other factors come into play here....the first thing you should do is adjust your results with a margin for error of 5-10% because this stuff is all over the board with the methods used...

Nice chat but completely worthless... and seriously do you really think your going to get Toyota to dial it in tighter... please think about it will you?

Toyota is actually far more precise than the collective chalk board scribbles being put up... don't believe me?

Plug in an OBD device into your OBD port and collect engine performance data (while driving) into a program... Garmin sells one called the EC0-HD I thnk? It sells for about $75 US as an add-on to some of their NUVI GPS units...then compare those results to your car computer results... want to bet how it turns out?

Seriously folks there are so many factors that impact your individual calculations that to get to within 5% will be more luck than anything else...

I can save you all $75. on the ECO-HD gizmo (which is kind of a cool gizmo) ... here is how->->-> Trust the car... Toyota is far closer to the real number than most of you will ever get... trust it.... I mean ...it's great isn't it go with it ?

 

2011 Prius

294 miles
5.962 gallons
Displayed 53.1
Ave speed 37
Actual 49.3
Difference 3.8 miles or 7.1%




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I just posted 7.5 years worth of calc vs display data here:
http://priuschat.com/forums/gen-ii-...90-updated-mpg-display-bias-calculations.html

 

2012 Prius Two - First fill by dealer. Most of my driving the first 1 1/2 weeks was to work, 28 miles one way, about 14 miles on the highway at 55 MPH. Tires filled by dealer with nitrogen. Checked last weekend and found 33 PSI front and rear. Adjusted front tires to 35 PSI, per specs - with air pump (not nitrogen). Drove very cautiously, 55 MPH on highway instead of 65 MPH. Slow acceleration, gliding to stops (or regenerative breaking), EV whenever possible.

Indicated 59.9 mpg (down from 60.0 mpg right before I entered gas station).
Mobil gas at 7-Eleven, up to 10% ethanol - regular gas.
530.3 miles, 9.281 gallons - 57.1 mpg, or 5% less than indicated.

This is my first Prius, and my goal was to get 60 mpg on my first tank. I did it, if I believe the trip computer.

I don't agree that we're lucky to get actual within 5% of computer. My last car, a Volvo V70, was right on the money. The car before that, a mini Cooper, was very optimistic. It looks to me like "efficient" cars tend to be optimistic.

 

The mini is not an efficient car, quite on the contrary, at least here in EU is seen as a (mini) gas guzzler. The Honda Insight is an efficient car and is spot on. The Yaris of my brother is older and far cheaper than my Prius and both tachometer and MFD are far more accurate than my Prius.

The purpose of this thread is not to complain about whether 5% is good or bad, but to assess if it changes over time, over temperature, over different revision of Prius (i.e. MY 2010 vs. MY 2012), over locations (e.g. EU vs. USA), over gas stations and so on.
And it looks like that 5-6% is the average MFD over estimation *worldwide*. As more MY 2012 owner show up on PC we will get an idea of whether Toyota fixed, or felt it had to fix, it's MFD.

I am personally of the opinion that 5% is still OK, as long as it constant over several tanks. It is my personal opinion that most gas stations are cheating about 1-3% in volume, and the rest is errors introduced either at the pump, gas volume depending on the temperature, etc.

Moreover another purpose of the thread is to reassure PC forum members and newbies that there is nothing wrong with their cars, and that 5-7% error is "normal" behavior.

I wonder if there is any other Internet resource that shows with accuracy the MFD error on fuel consumption of other car manufacturers. I think there would be a lot of surprises.