LPG mpg equivalent to petrol mpg

Just filled up my V8 with LPG so I now know what mpg I'm getting on it now.

Now I want to calculate the equivalent petrol mpg I would be getting if I was paying petrol prices, but don't know how, and googling hasn't really helped.

Anyone able to explain how?

Assuming you get the same mpg on LPG as you do petrol, you can work it out like this;

Edited
If LPG is 40% cheaper than petrol, you are getting 40% more miles for your money than you would on petrol. So if you take your fuel consumption of say 20 mpg, and multiply it by 0.4 (40% of it), you get 8. Add that to the original figure of 20 and you get your equivalent figure of 28mpg.

Think that is right. Add in your own figures and try it out

Cheers Langers, I just worked it out before you posted.

What I did was take the cost of how much I spent on lpg and divided it by the price of petrol, giving me the litres of petrol I would have got then just the normal mpg calculation.

Sound about right?

If so, would give the equivalent of 32.2mpg, not too bad!

gooselogan said:

Just filled up my V8 with LPG so I now know what mpg I'm getting on it now.

Now I want to calculate the equivalent petrol mpg I would be getting if I was paying petrol prices, but don't know how, and googling hasn't really helped.

Anyone able to explain how?

Click to expand...

Same for petrol or LPG. Start with a full tank. Zero the tripometer. When near empty fill up again and note the miles covered and the amount of fuel taken to fill up. Multiply the litres by 0.22 to convert to gallons. Divide the miles by the gallons to get the MPG.
To get the price per gallon multiply the litre price by 4.55
To get the price per mile divide to cost of the re-filled tank (in pence) by the number of miles covered.

That should cover most of what you want. If not post the figures and I will work it out. From experience you will get fewer MPG on gas than petrol.............but it's still cheaper.

gooselogan said:

Cheers Langers, I just worked it out before you posted.

What I did was take the cost of how much I spent on lpg and divided it by the price of petrol, giving me the litres of petrol I would have got then just the normal mpg calculation.

Sound about right?

If so, would give the equivalent of 32.2mpg, not too bad!

Click to expand...

Yeah that sounds spot on, think mine was just gibberish

gooselogan said:

Cheers Langers, I just worked it out before you posted.

What I did was take the cost of how much I spent on lpg and divided it by the price of petrol, giving me the litres of petrol I would have got then just the normal mpg calculation.

Sound about right?

If so, would give the equivalent of 32.2mpg, not too bad!

Click to expand...

Sorry........I sort of got the wrong end of the stick. Yep that works!

trucker5774 said:

Multiply the litres by 0.22 to convert to gallons.

Click to expand...

So hows that work then?
I thought it was 4.54 Lt to a gallon.............

Simples.

Just divide the price you paid to fill up by the cost per litre of LPG and then multiply the result with the cpst per litre of unleaded. That's what it would have cost!

ruffday said:

So hows that work then?
I thought it was 4.54 Lt to a gallon.............

Click to expand...

Get your calculator out ....enter 4.54 x 0.22 and press =

I think you will find that is 0.9988 That's close enough for me

trucker5774 said:

Get your calculator out ....enter 4.54 x 0.22 and press =

I think you will find that is 0.9988 That's close enough for me

Click to expand...

That maybe but why not just divide the total anout of lt by 4.54.

ruffday said:

That maybe but why not just divide the total anout of lt by 4.54.

Click to expand...

coz I'm lazy and there are less numbers involved and it's easier to remember

MMM, mine is doing about 8.4 mpg on LPG - ( just did 97 miles on 55 litres 50/50 stop start/motorway )
apart from selling the bugger any have any tips for improving on that?

From memory,lpg has about 80% energy of petrol,so need to factor that in to be a true comparison

yes i'd heard that - seems about right then
i was beginning to think it was leaking out somewhere
NO SMOKING in the rear !!!

Just worked it out on mine and I'm getting about 14mpg on LPG pottering about the place, in a 3.9 88" series 3. Sure that makes it cheaper to run than the Diesel equivalent.

had an lpg astravan, it was way less efficient on lpg, so used to work out miles against cost of fuel for both to make a comparison

did about 25mpg on lpg and about 33 on petrol