fuel consumption formula?

[ramblingboy42]

what is the correct way ....or formula.....for caculating fuel consumption in litres/100km?

I have recently seen differing methods with differing results?

for example use 456km on 52litres.

[frantic]

what is the correct way ....or formula.....for caculating fuel consumption in litres/100km?

I have recently seen differing methods with differing results?

for example use 456km on 52litres.

Divide 52 by 4.56(km divided by 100)=11.4 litres per 100kms.

To test its correct it should be able to go backwards , 11.4 x 4.56= 52.

[bee utey]

The intuitive answer is to mentally convert the km to 100's of km by moving the decimal point two spots to the left, ie 456km equals 4.56 hundreds, then divide 52 litres by 4.56 hundreds km and you get 11.4 l/100km

Or mathematically (52/456) x 100

[Homestar]

Remember that some people - like my Father in law - use KM per litre, which is backwards to L/100KM. It is the same figure when your at 10.0 but skew wiff either side of that.

My FIL says he's getting 7.5 but he really means around 13.3. :D

[ramblingboy42]

thanks guys...I've always done (52/456)x100

some of the fuel figures espoused on this site make me wonder if they're using correct calculus.

[V8Ian]

I have to convert to MPG for relevance, l/100 and kpl are just numbers.

[Saitch]

I have to convert to MPG for relevance, l/100 and kpl are just numbers.
I tend to agree Ian.
Why did we always have "Distance from Usage" & then suddenly
" Usage in 100 klms". Why :confused:
Surely knowing that if your fuel capacity is say, 95 litres & you get 9.5 klm per litre it's an easier bit of maths (95x9.5) than using the litres/100k formula.
Maybe I'm just a dumb old fart?
Steve

[vnx205]

if you are going to talk about fuel "consumption", then logic dictates that you should express it as the amount of fuel "consumed" for a set distance.

Kilometres per litre, miles per gallon, furlongs per tank, or leagues travelled until I decide to fill up may be a measure of something, but it is not a measure of "fuel consumption".

As far as convenience goes, the example in the previous post is no more sensible or convenient than using litres per hundred kilometres. A more common situation than the one described above is that you have destination to reach and you can more easily calculate how much fuel you will use or whether you will make it on one tank by using litres/100km.

For example, your trip is 350 km and you know your gas guzzling V8 uses 20 litres/100km. It isn't hard to calculate that you will need 70 litres, so if your tank holds 75 litres, you won't have much in reserve when you arrive.

While we can all think of examples where your starting point might be the amount of fuel you are starting with, in the real world, your starting point is more often the distance to be covered. It is more likely that you will find your self thinking that your trip around Australia with a few deviations will cover about 18,000km, so if you trade in the V8 and get a modern turbo diesel that can manage 10 l/100k, you will have to budget for about 1800 litres of fuel instead of 3600 litres.

It is much less likely that you will find yourself in a position where SWMBO has dictated that you are only allowed to buy 2000 litres of fuel and it is up to you to work out how far you will be able to go.

Regardless of what you think is more sensible, convenient or logical, the official way of expressing fuel consumption is litres/100km, so you will just have to get used to it. :p

BTW, I am curious to know how anyone could attempt to measure consumption in litres/100 km without using the method described above. How could anyone get a different result? :)

[vnx205]

I tend to agree Ian.
Why did we always have "Distance from Usage" & then suddenly
" Usage in 100 klms". Why :confused:
... ....
Steve

Probably for the same reason that I had to spend time in school learning pounds, shillings and pence; as well as ounces, pounds, hundredweights, tons; as well as inches, feet, yards, chains, furlongs, leagues; and so on. Schoolchildren don't have to so that now.

Like the conversion to metric, we have moved on to a more logical, convenient system. :)

[ramblingboy42]

I had a guy swear black and blue that if you shift the decimal point for km two places you must also shift the fuel amount two places and divide it into the km....like the old way

you end up with 8.7 instead of 11.2.

I think some people are doing that.

[Tombie]

L/100km makes certain calcs easy...

If I am going to drive 700 km to Coober Pedy, and I get 12l/100km then I will need 700/100*12 = 84 litres

Can I carry 84 litres? > Yes.. Good to go...

(Corrected the missing part of the formula)

[Grappler]

Here is a spread sheet. Just enter your distance and volume and e formula does the rest....I hope

[BMKal]

L/100km makes certain calcs easy...

If I am going to drive 700 km to Coober Pedy, and I get 12l/100km then I will need 700/12 = 58.33 litres

Can I carry 58.33 litres? > Yes.. Good to go...

Not by my calculator. :)

If you are using 12 litres per hundred kilometres and you want to travel 700km, then you will need 7 x 12 litres = 84 litres for the journey. :D

[vnx205]

L/100km makes certain calcs easy...

If I am going to drive 700 km to Coober Pedy, and I get 12l/100km then I will need 700/12 = 58.33 litres

Can I carry 58.33 litres? > Yes.. Good to go...

Sorry, but if you set off with 58.33 litres, then you ran out of fuel about 2/3 of the way there.

The calculation is simpler than you suggested.

Multiplication is generally easier than division and that is the operation you needed.

Think of it this way, you use 12 litres per 100km. There are 7 lots of 100 km in your journey, so you will use 7 lots of 12 litres. That is 84 litres.

That multiplication is easier than the division that you did (which gave you the wrong answer). :)

EDIT BMKal can obviously type ore quickly than I can. :)

[Saitch]

When travelling I still prefer to work out how many klms I can get out of my tank.
I know it's 90 litres & I get around 12 klms to the litre highway & can get down to 9 otherwise so, when I'm at 1/2 a tank & doing it a bit tough using the 9 litres say, I would work on another 360 klms, factoring in a buffer, not how many blocks of a 100 klms I can go.
Steve

[Tombie]

Yup.. You are correct. I messed my own calc up!

[Tombie]

Not by my calculator. :)



If you are using 12 litres per hundred kilometres and you want to travel 700km, then you will need 7 x 12 litres = 84 litres for the journey. :D


Yeah you got me. :D

Been a long day and I transposed a formula in my head!!!

[d2dave]

When I was growing up the whole idea of knowing fuel consumption was to give an idea of running costs, not how far one can go.
This is what the fuel gauge was for. When it started to get low it was time to fill up

And we used miles per gallon, not how many gallons per 100 miles.

So if we used miles per gallon, why the hell when we went metric is it not Kms per litre?

[vnx205]

Just because we used to refer to "miles per gallon" does not mean that was the most logical or convenient way to express fuel consumption.

After all we used to have twelve pennies in a shilling and twenty shillings in a pound. When we changed to dollars and cents, should we have kept the same illogical relationships?

The only reason people think "miles per gallon" is better is that it is the system they grew up with and to which they have become accustomed. If they had grown up with fluid ounces per ten furlongs, they would be using exactly the same argument to retain that system as they advance in support of mpg.

The only reason some people have a problem with litres/100km is because no-one likes to change from the way they learned to do things and the way they learned to think.

There is nothing wrong with litres/100km and even if there was, it is here to stay; get used to it. :)

[DiscoMick]

Being numerically challenged, I just downloaded a fuel consumption app to my phone. It gives a choice of l/100km, which I use, or others. All I need is distance travelled since last refill (set trip meter when refill) and amount of fuel put I have put in and up it comes.

[Pedro_The_Swift]

Litres per 100kays means nothing to me,,
its a calc used after you return from the trip.

[superquag]

...Just to add a bit of fuel to the fire...

IF you're of a Senior vintage, and still pine for the Good 'ole MPGs, then this is the easy way...

First work out the kms per litre. Your trip meter....divided by the number of litres on the bowser.

Then, multiply that by 2.8248093 - which will do both conversions and give you the answer in MPG

eg, 410km on 29.2 litres = 14.041 kms per litre.

X 2.8248093 = 39.6634 MPG

39.6 MPG is only a measure of "Economy", the more the better, whereas the cold, metric expression of 7.12 litres/100km is more useful for calculating 'useage' / co$t.

IMHO, both are useful for what they are.
:D

[goingbush]

I use this online calculator

https://motormouth.com.au/myvehicle/consumptioncalculator.aspx

[landy]

Guys, guys! Whoa!
I've tried to read this thread. But frankly it's three pages of blah blah blah. I'm not that smart haha.
Just down load Roadtrip to your smart phone. Does it all. L/100km MPG and keeps track, easy!
Hope this helps the mathematically challenged!

[Chops]

First work out the kms per litre. Your trip meter....divided by the number of litres on the bowser.

eg, 410km on 29.2 litres = 14.041 kms per litre.



This is how I do it, and it seems to work well :D
It allows me to estimate how far I can go at any time basically. Now, knowing I get roughly 600K to the tank, approx 60 odd litres, by looking at the trip meter which is reset at every full fill, its easilly worked out.

[biggin]

Doesn't make any difference to me. 16.8 is what I usually average. Mpg or l/100km! [emoji4]

[Grappler]

Doesn't make any difference to me. 16.8 is what I usually average. Mpg or l/100km! [emoji4]

simultaneous equation?:(

[d2dave]

Guys, guys! Whoa!
I've tried to read this thread. But frankly it's three pages of blah blah blah. I'm not that smart haha.
Just down load Roadtrip to your smart phone. Does it all. L/100km MPG and keeps track, easy!
Hope this helps the mathematically challenged!

Don't have a smart phone.

[DiscoMick]

This is how I do it, and it seems to work well :D
It allows me to estimate how far I can go at any time basically. Now, knowing I get roughly 600K to the tank, approx 60 odd litres, by looking at the trip meter which is reset at every full fill, its easilly worked out.

Yep, that's what the app. I downloaded does - basically just a calculator.