Conversion Calculator for Units of
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select units . . .
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Values are shown to . . . significant figures.

miles / gallon(UK)
gallons(UK) / 100 miles
km / gallon(UK)
gallons(UK) / 100 km
miles / litre
litres / 100 miles
km / litre
litres / 100 km
miles / gallon(US)
gallons(US) / 100 miles
km / gallon(US)
gallons(US) / 100 km
metric measures are shown in red.
Very large and very small numbers appear in e-Format and have not been spaced.
Unvalued zeros on all numbers have been suppressed.
NO guarantee as to the accuracy of these values is given.
And they should be checked against some other source.
This is a measure which many people use at some time or other, even if it is only in a casual rather than a calculated way. This is in connection with the motor-car, saying how much it "drinks" in miles per gallon (mpg). Here there are two units involved (distance/volume), either or both of which can be changed so we could have 'miles per litre' or 'kilometres per gallon' or 'kilometres per litre' and so on - whatever happens to be convenient.
Fuel consumption can also be stated in another way, by saying how much fuel is needed to make the car go a particular distance. This could be put as gallons per mile. However, unless we were describing the fuel consumption of a jumbo-jet, this figure would be rather small.
For example, a car doing 35 mpg uses about 0.0286 gallons per mile.
To make this figure more "friendly" it is usual to state the amount of fuel needed to go a greater distance - say 100 miles. Now 35 mpg becomes 2.86 gallons per 100 miles. In terms of planning fuel requirements for a trip this form is more directly usable. In fact the metric way of expressing fuel consumption has always been in litres per 100 kilometres.
The fuel consumption of 'ordinary' cars in 'ordinary' use varies between 30 and 50 miles per gallon, depending upon care and conditions. The size of the engine (and its condition), the weight of the vehicle, speed (and how much it varies), hills, length of the journey, are just some of the factors that affect how much fuel is needed for a given distance.
In very special record-breaking attempts, on a track, in a purpose-built vehicle (holding only one person), petrol consumptions of nearly 8,000 miles per gallon have been achieved!
The record breaking attempts of 'ordinary' cars (carefully tuned and driven) on level roads are more usually not much over 100 miles per gallon.
Note that all of this is directed towards vehicle movement.
Fuel consumption can arise in other circumstances.
For example, the fuel-flow to an engine might be measured in terms of mass per unit of time (kg/minute, pounds/hour etc.) or volume per unit of time (litres/second, cubic metres/hour etc.). These are referred to as 'mass rate of flow' and 'volume rate of flow' respectively and are dealt with in separate conversion calculators.
Alternatively, an engine (of any type) used to drive a generator might have its fuel consumption measured in terms of fuel used (in gallons, litres, kilograms etc.) per measure of electricity generated (kilowatt-hours etc.)