Fuel consumption describes how much fuel a vehicle uses to cover a given distance. In metric markets it is commonly expressed as litres per 100 kilometres (L/100 km), while specifications and travel information may also use km/L or MPG.
A related practical question is how much fuel a planned route will require and what that fuel will cost at a given price. That is a planning calculation: trip distance is combined with the vehicle's average fuel economy, then required fuel is combined with the price per litre or gallon.
This guide covers both tasks: measuring actual consumption from real distance and fuel used, and estimating the fuel and cost of a future trip.
What fuel consumption means
The same physical fuel economy can be written in different ways. With L/100 km, a lower number means less fuel used. With km/L or MPG, the direction is reversed: a higher number means the vehicle covers more distance per unit of fuel.
For example, 7.5 L/100 km means that under the stated conditions the vehicle requires about 7.5 litres to travel 100 km. It is a consumption rate, not a guarantee that every future 100 km will produce exactly the same result. Speed, traffic, temperature, terrain, load and driving style can all change real-world consumption.
How to calculate actual fuel consumption
If you know the actual distance travelled and the actual fuel used, the main formula is:
Fuel consumption, L/100 km = fuel used, L ÷ distance, km × 100
Suppose a vehicle travels 500 km and uses 37.5 L:
37.5 ÷ 500 × 100 = 7.5 L/100 km
The same result can be expressed as kilometres per litre:
km/L = distance, km ÷ fuel, L
For this example:
500 ÷ 37.5 = 13.333... km/L
Both values describe the same physical efficiency, but they use opposite conventions: lower is better for L/100 km, while higher is better for km/L.
L/100 km, km/L and MPG: how the units differ
When comparing vehicles or data from different countries, the unit system matters. LUKIK normalizes calculations through kilometres and litres, then presents equivalent values in the supported systems.
- L/100 km — litres required to travel 100 km;
- km/L — kilometres travelled per litre;
- MPG (US) — miles per US gallon;
- MPG (UK / Imperial) — miles per Imperial gallon.
The L/100 km conversions use different constants:
MPG (US) = 235.214583... ÷ L/100 km
MPG (UK) = 282.480936... ÷ L/100 km
Why MPG (US) and MPG (UK) must stay separate
A US gallon and an Imperial gallon are different volumes. One US gallon is approximately 3.785411784 L, while one Imperial gallon is 4.54609 L. As a result, the same physical fuel consumption produces different MPG numbers.
At 7.5 L/100 km, the equivalents are approximately:
- 31.362 MPG (US);
- 37.664 MPG (UK).
That is why a bare value such as “30 MPG” can be ambiguous unless the gallon system is identified.
How to measure real consumption with the full-to-full method
A practical way to estimate a vehicle's actual consumption is to measure the interval between two comparable full refuelling stops.
- Fill the vehicle to your normal automatic pump cut-off.
- Reset the trip meter or record the odometer reading.
- Drive a distance that represents your normal use.
- Refill to the same practical level.
- Use the distance travelled and the fuel added at the second fill.
- Apply the L/100 km formula.
A very short interval may not represent typical use. For planning, a longer sample that resembles your real driving conditions is usually more useful than a single unusually short journey.
How to calculate fuel required for a trip
If the vehicle's average consumption is already known, required fuel is calculated from route distance:
Fuel, L = distance, km × consumption, L/100 km ÷ 100
For a 500 km route at 7.5 L/100 km:
500 × 7.5 ÷ 100 = 37.5 L
For a return trip, double the distance once. A 500 km one-way route becomes 1000 km total:
1000 × 7.5 ÷ 100 = 75 L
The LUKIK calculator provides a dedicated round-trip toggle so the distance is doubled exactly once.
How to calculate trip fuel cost
Once the required fuel amount and the matching fuel price are known:
Trip cost = required fuel × fuel price
For 37.5 L at 60 UAH/L:
37.5 × 60 = 2250 UAH
For the 75 L return-trip example:
75 × 60 = 4500 UAH
The calculator can also show cost per kilometre or mile and per 100 km or 100 miles. Currency in the tool is display metadata only: it does not fetch exchange rates or convert one currency to another.
Calculate fuel consumption and trip cost with LUKIK
Worked examples with MPG and gallons
300 miles at 30 MPG (US)
At 30 MPG (US), a 300-mile trip requires:
300 ÷ 30 = 10 US gal
That is approximately 37.854 L. At 3.50 USD per US gallon:
10 × 3.50 = 35.00 USD
The equivalent metric consumption is approximately 7.840 L/100 km.
250 miles at 45 MPG (UK)
At 45 MPG (UK) over 250 miles:
250 ÷ 45 = 5.555... Imperial gal
That is approximately 25.256 L. At 1.45 GBP per litre:
25.256 × 1.45 ≈ 36.62 GBP
This example again shows why the gallon system must be known before calculating or comparing MPG values.
Why real-world fuel consumption can differ
The arithmetic is exact for the values entered, but the inputs themselves can vary between journeys. Real consumption can change with speed, urban or motorway driving, traffic, temperature, engine warm-up, tyre pressure, vehicle load, terrain, wind, mechanical condition and acceleration or braking style.
For that reason, LUKIK v1 does not add universal buttons such as “winter +8%” or “air conditioning +7%”. Fixed adjustments would imply the same effect for very different vehicles and conditions. For planning, it is better to enter an average consumption figure that actually represents the journey you expect to make.
Common calculation mistakes
Confusing L/100 km with km/L
They are not the same numeric value. 10 L/100 km happens to equal 10 km/L, but 8 L/100 km equals 12.5 km/L.
Using MPG without identifying US or UK
Different gallon sizes produce different results. LUKIK always keeps MPG (US) and MPG (UK) separate.
Doubling a return trip twice
A round trip requires the distance to be doubled once. The fuel formula is then applied to that effective total distance.
Entering a per-gallon price as a per-litre price
The price unit must match the value entered: per litre, per US gallon or per Imperial gallon.
Treating a published economy figure as a guarantee
For a practical trip budget, your own representative average consumption can be more useful when it is available and measured under similar conditions.
How the LUKIK calculator helps
The calculator has two separate modes. “Actual fuel consumption” uses real distance and fuel used. “Trip fuel & cost” uses route distance and a known average fuel economy.
It supports kilometres and miles, litres, US gallons and Imperial gallons, L/100 km, km/L, MPG (US) and MPG (UK). If a price is supplied, it adds monetary results without performing currency conversion.
Open the LUKIK Fuel Consumption & Trip Cost Calculator
Conclusion
Actual consumption needs two measured inputs: distance travelled and fuel used. Trip planning needs route distance and the vehicle's average consumption. A fuel price can then turn the required fuel amount into an estimated trip cost.
The key is to keep units consistent, distinguish MPG (US) from MPG (UK), and use an average fuel-consumption value that reflects the conditions of the journey you are planning.
FAQ
How do I calculate fuel consumption per 100 km?
Divide litres used by kilometres travelled and multiply by 100. For example, 37.5 L over 500 km equals 7.5 L/100 km.
Which is better, L/100 km or km/L?
Both express the same fuel economy. Lower is better in L/100 km; higher is better in km/L.
What is the difference between MPG (US) and MPG (UK)?
The gallon size is different. An Imperial gallon is larger than a US gallon, so the same physical consumption produces a higher MPG (UK) value.
Does the calculator account for traffic, winter or air conditioning?
No. It calculates from the average consumption you enter. For a realistic plan, use a value that represents your expected conditions.
Does LUKIK convert currencies?
No. Currency is used only to label the displayed result. Exchange rates are not fetched or applied.