Forum: Weblog comments

Further complicating the issue are the widely different energy densities of various fuels. Ethanol, for instance, contains only about three-quarters the combustion energy of an equal quantity of gasoline (petrol), which in turn contains about 30% or so less energy than diesel fuel. Both "miles per gallon" and "liters per 100km" are pretty broken measures of fuel efficiency when you take this into account. I blogged about this a while back if you're interested.

Even more confusing over here, where we are using miles for distances and fuel is sold in litres. Most people still seem to work in mpg (with a UK gallon rather than a US gallon), although l/100km is also quoted in places - but whatever you work in, if you want to calculate things based on how far you have driven and how much fuel you put in the car, you have to convert from miles per litre...