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Fuel Economy Calculator – Get Your *Real* MPG, L/100km

Petrol pump filling car

Is your garage giving the right amount of fuel. Is expensive fuel really more expensive?

Is your on-board computer telling porkies? Is it really more expensive to run your car on high octane fuel? Get the real number with these fuel economy calculators.

Enter the cost of the fill up, the price per litre and the distance travelled.

Quick Links: USA MPGUK MPGLitres/100km & UK MPG

Fuel Economy Calculator US (Miles per gallon US)

Fuel Economy Calculator UK (UK miles per gallon)

Fuel Economy Calculator World (litres/100km & UK MPG)

Why would the on board computer be inaccurate?


The engine sensors are critical to giving accurate figures but like anything else, sensors age and get inaccurate over time.


Remaps and chip tuning boxes can also massively effect fuel economy figures depending on how the tune is done and what modifications are done along with the remap/tuning box.


Conspiracy, I cant confirm this but is it possible the on-board computer from the factory is inaccurate to give owners the false impression of how efficient their car is? I do not know if this happens but our fuel economy calculator will tell you the reality.

Why did I make this fuel economy calculator?

Because I could not find an easy to use calculator online.

I just want to be able to put in distance travelled, price per litre and the cost of the fill up to get the number I want.

This calculator is helpful to me so hopefully you will find it helpful also!


In the US fuel economy calculator. You can also use it if your country uses miles to measure distance and prices the fuel in gallons. Just substitute dollars for your currency.

In the UK calculator. You can use it for any country where distance is measured in miles and fuel is sold by the liter.

Other Uses

Measure Fuel Pump Accuracy

You can also use these calculators to get an idea if the petrol station/gas station you use is dispensing the correct amount of fuel at the pump. You can compare fuel economy between gas stations/petrol stations to see if there are any noticeable differences.

I have done this. I thought some gas stations gave more fuel than others but I was wrong. All the gas stations I used gave me around the same range after I took into consideration where I was driving.

High Octane Fuels – Really More Expensive?

This calculator can also help identify if buying high octane fuel costs you more money or less money or does not make a difference at all.

In my testing I compared 100 octane wih 95 octane fuel. The range of the car did not change noticeably between the two different types of fuel.

Maybe this was because the prices are quite close but whatever the case maybe, by doing these calculations I now use 100 octane fuel whenever I can because it does not seem to cost any more, distance covered wise, and the engine seems much happier using high octane fuel

Share Your Fuel Economy Figures

It would be interesting to see the difference between cars of different ages and engine sizes eg are new cars really as efficient as they claim?

Leave a comment below with your:

Car details – Make, Model, Year, Engine Size (& Horsepower if relevant)

Type of driving

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This page was last modified May 19, 2022 @ 12:46 pm

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