calculated vs. computer MPG - Please post your results

Something's not right in the above: there's a wide difference between the two liter/100km values, but very little between the mpg values. Metric might be correct: there's roughly 12% difference between the two metric values.

Should maybe 50.3 mpg be more like 56?

 

Actually the difference is about 3% - (50.3/48.9-1)*100=2.86%.

50.3 MPG are 4.676L/100km, and 48.9MPG are 4.81L/100km, which still yields about 3% discrepancy ((4.81/4.67)-1*100=2.99%).

MPG and L/100km are not in linear relationship to each other, hence the discrepancy in calculated % difference.

Does your Prius report MPG or L/100km? or km/L?

 

Hi thanks for reply.

Sorry supposedly to be ...

HSI states 55.4 MPG (4.2 L/100km)
Calculated 48.9 MPG (4.75 L/100km) - difference of about 12%; too far for my liking

My Prius records in L/100km

To get km/L - I take 100 divide by L/100km

And then take the km/L divide by 0.43 to get MPG.

I see most of the forumers here use MPG, therefore I converted it for easy reference for discussion.

I am wondering why my reading is so much different between calculated and HSI?

 

I'm not seeing the huge difference between displayed and actual MPG that some people are reporting. I have a 2011 Prius with 4k miles on it. My last tank, filled up this morning, read like this:

Miles = 405.9
Gallons to refilll (first click-off always) = 8.827
HSI = 47.6 MPG
Actual = 45.984
Difference = 3.514%

Not of consequence, but I live in Central Texas where it has been in the triple digits for 50 days. The A/C in the Prius is on all the time. I also drive in Eco mode all the time. All that said, this is my first Prius and I absolutely love it!

Thanks,
Jeff

 

That's actually less than a 3% difference. Not 12%

 

Check his post #643, he corrects a value.


BTW, to convert liters/100km to US mpg, or back, do:

235.2 divided by either value

(235.2 is rough, you could add a few more decimal places, but it's close)

 

Or easier yet - www.convert-me.com (section "Fuel Economy")

 

Well, for use without the internet (shudder), just knowing a number is handy.

 

My HSI consistently reads about 3-4% higher than calculated. I am keeping a spreadsheet on my phone and my overall average in 10501 miles is 47.0083174MPG calculated. I walk to work so the driving is a mixture of local errands and a few longer trips. My best tank was 52.7MPG on a trip where the first 100 miles was at 55MPH and the rest was at 70MPH (HSI indicated 57MPH). My worst tank was 42MPG where we had a bunch of short errands over a three week period and the HSI indicated an average speed of 37MPH. Overall we are extremely happy with the Gen 3, our first Prius but our 14th Toyota.

 

Miles: 227.8

Gal's: 4.201

MPG Computer: 57.9

MPG Calculated: 54.225

10% Ethanol reg gas / Costco

 

I had my 2nd fill up recently (37.055L)

Total distance travelled - 830.7km

HSI states 4.3 L/100km (54.7 MPG)

Calculated 4.46 L/100km (52.73 MPG) - difference of about 3.6%; thats more like it!

 

Miles: 419.3
MPG Indicated: 57.8
MPG Calculated: 55.294

Reg gas/ with 10% Ethanol

85% hwy driving, from Sea level up
the Santiam Pass, 4,800 + feet, and fill
up in Bend Oregon, about elev. 3,600 feet

My wife and I with luggage at speeds 70 mph
to city speeds

Return to Seaside Oregon.

Arrive Seaside (elev. sea level)
Miles; 257.6
fuel used: 4.386 gal's
MPG Indicated: 63.7
MPG Calculated: 58.73

 

I had my 3rd refill up recently (38.16 L)

Total distance travelled - 868.6 km
Fuel consumed - 38.16 L

HSI states 4.1 L/100km (57.4 MPG)

Calculated 4.39 L/100km (53.6 MPG) - difference of about 6.7%

 

Very similar to mine. Did you stop fuelling at the first click or did you push it further for a couple of click after the first one?

 

First, I top off to the nearest 1/4 or 1/2 gallon at the pump or the nearest 50 cents depending on my mood - I've always done this since I started driving. The best was still around 60+ MPG in some post I think I had way back when about a trip to Maryland or Virginia on my first Prius 2005. Anyways the juicy stuff and comparisons going from Current to Past:

Current Prius Gen III - 2011 Prius II in Silver Classic
Mileage: 573 miles
Gasoline Consumed at Pump: 10.35 gallons
HSI: 52.3mpg over 553 miles
Calculated: (553/10.35) = 55.36 MPG
Avg. Octane Rating: 87 (10% Ethanol)
PSI of tire(s): 42PSI front, 40PSI rear
Background: Stock car. Driving conditions - mostly driven on the main line jam packed L.I.E./495 (Long Island, NY) until I get my clean pass. Light-foot & hyper-miling. This is my 3rd Prius from the same dealership and the same Salesman (more or less) who also now owns a Prius. *lol*

Past Prius Gen II - 2008 Prius in Silver Classic Package #02
Mileage: 39351 miles
Gasoline Consumed at Pump: 888 gallons
HSI average: 46.20mpg
Calculated: (39351/888) = 44.31 MPG
Avg. Octane Rating: 87 (10% Ethanol)
PSI of tire(s): 38 front and 36 rear? Basically whatever was recommended.
Vehicle Background: Stock Car. Spirited driving. Kept tire inflation at recommended levels for mainly for comfort for Wifey. Tire change at around 39100 miles to the Continental ProContact with EcoPlus. The tires were replaced in the summer. The tires were quiet and handled well in wet weather. Not going to speculate on mileage or snow conditions due to the short time I had them.

Past Prius Gen II - 2005 Prius in Seaside Blue Package #02
Mileage: 27,635 miles
Gasoline Consumed: 520.5 gallons
Averaged HSI: 48.6mpg (avg of each trip)
Actual MPG based on totals: (27635/520.5) = 53.09 MPG
Average Octane rating: 89 (New York has 10% ethanol)
PSI of tire(s): 42 PSI for all four tires.
Vehicle Background: Stock car, stock tires. Lightfoot conservative driving style. Hyper-miling used. Tire inflation 2 PSI less max. New toy...

 

This is my first post in this thread. Im so excited. I feel a part of the group. I have a 2004 Prius with 75000 miles.

I went 410 miles.
Filled my tank = 8 gallons
For a grand total of 51.25 mpg

My car read that my mpg was 53.7 mpg.

That equates to about (if I calculated right) a 4.5% difference.
By the way, does the cars mpg always reset when you refill?

 

I try to fill until it doesn't allow me; meaning getting a few clicks.

 

Then your 4.5% is pretty good - meaning that either the Prius you have is more accurate (at least compared to mine...) or your fuel pumps are more accurate than elsewhere...

 

Miles: 370.0
Gal's: 6.778
MPG Computer: 57.1
MPG Calculated: 54.588

Reg gas with 10% Ethanol

 

I filled to the top of the filler, drove 314 miles, filled to the top of the filler again and the computer said 47 mpg. Took 6.916. gallons. 45.4 mpg. I find that tolerable.