How to calculate petrol costs

Written by timothy banas
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How to calculate petrol costs
Cars generally burn less petrol than trucks. (yellow car, a honda Japanese sport car model image by alma_sacra from

When you are trying to decide which car to buy, or just figuring your budget for the next month, it can be valuable to calculate the petrol costs of your car or the one you might purchase. Cars burn petrol as fuel. Each type of car on the market has its own fuel burning characteristics, usually expressed in litres per 100 km (L/100km) or miles per gallon (mpg). You can typically find out a car's average L/100km or mpg for city driving, highway driving or combined. Knowing a car's L/100km/mpg rating and the current price of petrol is crucial to calculating your petrol costs.

Skill level:


  1. 1

    Find out the ratings of your car or the car you might buy. For instance, suppose the car gets 12.8 L/100km (22 mpg) in the city, 9 L/100km (30 mpg) on the motorway and 11 L/100km (25 mpg) city/motorway combined.

  2. 2

    Examine how you drive. To determine which rating you should use to calculate your petrol costs, think about where and how you drive. If most of your driving is stop and go, under 64 kilometres per hour (40 miles per hour), use the city rating. If most of your driving is cruising above 64 kph (40mph), use the highway rating. If you drive an even mix of both, use the combined. As an example, the combined L/100km rating of 11 L/100km (25 mpg) will be used.

  3. 3

    Estimate how many miles you drive in a week. Reset your car's trip odometer to 0 at the beginning of a typical week. At the end of the week, look at how many miles you drove. Suppose that in a typical week you drive 483 km (300 miles).

  4. 4

    Divide the number of kilometres by 100 the result should be multiplied by the rating. So 11 x 4.83 means you used 53 litres (12 gallons).

  5. 5

    Multiply your answer from Step 4 by the current price of petrol to calculate your petrol cost per week. As an example, suppose the current price of petrol is £1.30 per litre. Petrol cost per week = 53 litres x £1.30 per litre = £68.90. Your petrol cost would be £68.90 per week.

Tips and warnings

  • Since the price of petrol is ever changing, you can give yourself some leeway in your budget by using a higher price to calculate your petrol cost. That way, if the price of petrol rises, your budget will not suffer for it.

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