Jack
02-10-10, 01:30 PM
There's been quite a few questions about what MPG people get from different car/engine combinations lately. Many people simply post miles per £ of petrol, which is fine but then considering the value of petrol varies so much across the board its not a reliable measure.
To get calculate the MPG, you will need to know either:
Litres
or
Total Cost and Pence Per Litre
How to calculate MPG if you know the quantity of petrol (litres)
This is quite simple, all you're essentially doing is dividing the miles driven by the amount of fuel. As almost all the pumps in the UK deal in metric Litres, you'll then want to convert to gallons - there's 4.546 litres in a UK gallon, so all thats needed there is a simple multiplication.
Miles / Litres x 4.546 = MPG
Example:
90 miles on 8.5 litres:
90 / 8.5 x 4.546 = 48.12
How to calculate MPG if you know the price of the petrol
This time, we don't know the quantity in litres, but we do know the total cost and pence per litre. All we need to do is just figure out how many litres that total cost has bought us, then we can proceed as above.
Cost (in pence) / Pence Per Litre = Litres
Miles / Litres x 4.546 = MPG
Example:
105 miles on £23 at 120.9ppl
2300 / 120.9 = 19.02
105 / 19.02 x 4.546 = 25.10
Getting an accurate calculation
Obviously the more specific your numbers are, the more accurate your calculations will be, so its wise to use a couple of decimal places - don't go overboard.
If you want to keep an eye on your MPG, consider keeping a log of fillups. Each time you refuel, note down how much you put in (and the price if you like) and your car's mileage. Over time you can then create a picture of your MPG, allowing you to see what mods/actions have affected your cars running.
The most accurate way to track regular MPG is to fill the tank to the brim each time you refuel. Whilst you don't then have to use ALL that petrol each time, your calculations will look a lot better if you top the tank each time.
There are a whole load of online mileage trackers out there - have a look on google for things like MyMileageTracker, Fuelly, etc. These will do most of the calculations for you, and some even have the capacity for keeping records of modifications and servicing schedules!
To get calculate the MPG, you will need to know either:
Litres
or
Total Cost and Pence Per Litre
How to calculate MPG if you know the quantity of petrol (litres)
This is quite simple, all you're essentially doing is dividing the miles driven by the amount of fuel. As almost all the pumps in the UK deal in metric Litres, you'll then want to convert to gallons - there's 4.546 litres in a UK gallon, so all thats needed there is a simple multiplication.
Miles / Litres x 4.546 = MPG
Example:
90 miles on 8.5 litres:
90 / 8.5 x 4.546 = 48.12
How to calculate MPG if you know the price of the petrol
This time, we don't know the quantity in litres, but we do know the total cost and pence per litre. All we need to do is just figure out how many litres that total cost has bought us, then we can proceed as above.
Cost (in pence) / Pence Per Litre = Litres
Miles / Litres x 4.546 = MPG
Example:
105 miles on £23 at 120.9ppl
2300 / 120.9 = 19.02
105 / 19.02 x 4.546 = 25.10
Getting an accurate calculation
Obviously the more specific your numbers are, the more accurate your calculations will be, so its wise to use a couple of decimal places - don't go overboard.
If you want to keep an eye on your MPG, consider keeping a log of fillups. Each time you refuel, note down how much you put in (and the price if you like) and your car's mileage. Over time you can then create a picture of your MPG, allowing you to see what mods/actions have affected your cars running.
The most accurate way to track regular MPG is to fill the tank to the brim each time you refuel. Whilst you don't then have to use ALL that petrol each time, your calculations will look a lot better if you top the tank each time.
There are a whole load of online mileage trackers out there - have a look on google for things like MyMileageTracker, Fuelly, etc. These will do most of the calculations for you, and some even have the capacity for keeping records of modifications and servicing schedules!