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Gas per km Calculator: How to Work It Out

Updated · Standard formula, shown below

Fuel consumption 8.00 L/100km
Cost per km
0.12 per km
Result
Cost per 100 km
12.00 per 100 km
Result
Distance
100 km
You entered

Gas per km Calculator: How to Work It Out

This calculator works out your fuel consumption in litres per 100 kilometres (L/100 km) and the cost per kilometre, based on the distance you travelled, the fuel you used, and the price you paid. You enter the distance driven, the fuel used in litres, and the fuel price per litre; you get back your average fuel consumption and the cost per kilometre. It is the standard metric way to measure a car’s fuel efficiency in most of the world.

Formula

The fuel consumption in litres per 100 kilometres is:

FC = (F ÷ D) × 100

  • FC = fuel consumption in litres per 100 km (L/100 km)
  • F = fuel used in litres (L)
  • D = distance driven in kilometres (km)

The cost per kilometre is:

Cost per km = P × F ÷ D

  • P = fuel price per litre (currency/L)

The cost per 100 km is simply the cost per km multiplied by 100.

Worked Example

Using the default values: distance = 100 km, fuel used = 8 L, price = 1.50 per litre.

  1. Fuel consumption = (8 L ÷ 100 km) × 100 = 8.00 L/100km
  2. Cost per km = 1.50 × 8 ÷ 100 = 0.12 per km
  3. Cost per 100 km = 0.12 × 100 = 12.00 per 100 km

So with those numbers, the car uses 8 litres of fuel for every 100 km, costing 12 currency units per 100 km.

How to Measure Your Own Fuel Use

The most accurate way to get the inputs is the “full tank to full tank� method:

  1. Fill the tank completely and note the odometer reading (or reset the trip meter).
  2. Drive normally for as many kilometres as you can – the more, the better (at least 300 km).
  3. Fill the tank completely again. The amount of fuel pumped is exactly what you used.
  4. Note the new odometer reading. Subtract the first reading to get the distance.

Enter those two numbers into the calculator. This method smooths out daily variations from hills, traffic, and weather.

What the Result Means

A lower L/100km number is better – it means the car uses less fuel for the same distance. Typical values:

  • Small city car: around 5–6 L/100km
  • Midsize sedan: around 7–9 L/100km
  • Large SUV or pickup: 10–14 L/100km
  • Hybrid: 3–5 L/100km

Note that official fuel consumption figures (from laboratory tests) are usually lower than real-world numbers. Your actual result depends on driving style, traffic, tyre pressure, air conditioning use, and load.

Common Mistakes and Misconceptions

  • Mixing up units: The calculator uses kilometres and litres. If you measure distance in miles, convert to km first (1 mile = 1.60934 km). If you measure fuel in gallons, convert to litres (1 UK gallon = 4.546 L, 1 US gallon = 3.785 L).
  • Not filling the tank completely: If you don’t fill to the same level each time, the fuel used won’t match the distance driven.
  • Short trips: A 10 km trip will give a very inaccurate reading because the tank level reading is coarse.
  • Confusing L/100km with km/L: Some countries use km per litre (km/L). To convert: km/L = 100 ÷ L/100km. For example, 8 L/100km = 12.5 km/L.
  • MPG confusion: Miles per gallon (MPG) is common in the US and UK. To convert L/100km to US MPG: MPG = 235.215 ÷ L/100km. To convert to UK MPG: MPG = 282.481 ÷ L/100km.

Why It Matters

Knowing your car’s real fuel consumption helps you:

  • Budget for fuel costs on a trip or for a monthly commute.
  • Compare your car’s real efficiency with official figures.
  • Spot problems early – a sudden increase in fuel use can indicate under-inflated tyres, a dirty air filter, or an engine issue.
  • Choose a more efficient car when you’re buying.

Limits of This Calculator

This calculator gives an average over the distance you entered. It doesn’t account for:

  • Driving conditions (city vs. highway, hills, stop-and-go traffic).
  • Weather (cold starts, headwinds, rain).
  • Vehicle load and towing.
  • Fuel quality and ethanol content.

For the most accurate picture, measure over several tanks and take the average.

Frequently Asked Questions

How do I convert L/100km to MPG?

Divide 235.215 by the L/100km value to get US MPG, or divide 282.481 by the value to get UK MPG. For example, 8 L/100km is about 29.4 US MPG (235.215 ÷ 8) and 35.3 UK MPG (282.481 ÷ 8).

What is a good L/100km figure?

For a modern petrol car, anything under 6 L/100km is very good; under 5 is excellent. For a diesel, under 5 is good. For a large SUV, 10 or higher is typical. Hybrids often achieve 3–4 L/100km.

Why is my car’s real fuel consumption higher than the official figure?

Official tests are done in controlled conditions with specific driving cycles that don’t include real-world factors like traffic, air conditioning, roof racks, or aggressive acceleration. Real-world figures are typically 10–20% higher.

Can I use this calculator for a trip to estimate fuel cost?

Yes. Enter the total trip distance, your car’s average fuel consumption (from the calculator or the owner’s manual), and the current fuel price. The cost per km output will give you the total cost when multiplied by the trip distance.

What’s the difference between L/100km and km/L?

L/100km is litres used per 100 km – lower is better. km/L is kilometres per litre – higher is better. To convert km/L to L/100km, divide 100 by the km/L value. For example, 12.5 km/L = 8 L/100km.

Related

Formula used
in d | Distance | km | 100 | 0
in f | Fuel used | L | 8 | 0
in p | Fuel price | per L | 1.50 | 0
out fc | Fuel consumption | L/100km | f / d * 100 | 2
out cp | Cost per km | per km | p * f / d | 2
out cf | Cost per 100 km | per 100 km | p * f / d * 100 | 2

Each line is one input (in, sel, list) or one result (out: label, unit, formula, decimals). How the calculators work

Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.