Knowing what a drive will actually cost changes decisions. A road trip that looks expensive at first glance might be cheaper than the train once you split fuel across three passengers. A “cheap” weekly commute in a thirsty SUV can quietly cost as much as a car lease. This fuel cost calculator combines distance, efficiency, fuel price, and passenger count to give you a straight answer, works in both metric and imperial units, and accounts for the gap between official ratings and real-world consumption.

How fuel cost is calculated

Metric (L/100 km)

Europe, most of Asia, and Australia express fuel efficiency as litres per 100 km — how much fuel it takes to travel 100 km. A lower number means a more efficient car.

Total cost = (distance / 100) × efficiency × price per litre

Example: 500 km trip in a car that uses 6.5 L/100 km, with diesel at €1.80/L:
(500 / 100) × 6.5 × 1.80 = €58.50

Imperial (MPG)

The US and UK use miles per gallon — a higher number means a more efficient car. Crucially, a US gallon (3.785 L) is about 20% smaller than a UK gallon (4.546 L), so the same car has different MPG figures on each side of the Atlantic.

Total cost = (distance / MPG) × price per gallon

Example: 300 miles in a car rated 35 MPG, with gas at $4.10/gallon:
(300 / 35) × 4.10 = $35.14

Manufacturer ratings vs. reality

Official fuel-economy figures come from standardized test cycles: WLTP in Europe, EPA in the US, CLTC in China. The real-world number is almost always worse, because the tests:

Run at modest speeds (never highway cruising at 130 km/h)
Warm the engine beforehand (no cold starts in stop-and-go traffic)
Ignore climate control, roof racks, and headwinds
Use optimal gear ratios and ideal tire pressure

Typical real-world vs. rated gaps:

WLTP (Europe, post-2017): real-world usually 10–20% worse
EPA combined (US): usually within 5–10% of reality
NEDC (Europe, pre-2017): frequently 25–40% worse, which is why it was replaced

If you’re entering a number for long-term budgeting, check your trip computer or log a few tank-to-tank averages rather than using the brochure figure.

Factors that affect consumption

Speed. Aerodynamic drag scales with the square of speed. Going from 100 km/h to 130 km/h increases fuel use by roughly 25–30% on most cars.
Acceleration style. Hard accelerations waste fuel; smoother inputs can improve economy by 10–20%.
Cold starts and short trips. A cold engine runs rich for the first few kilometres. A 2 km shop run can use 2–3× the fuel of the same distance on a warm engine.
Weight. Every extra 100 kg costs about 0.3–0.5 L/100 km. Empty out the boot before a road trip.
Roof boxes and bike racks. A roof box can add 10–20% to highway consumption; a bike rack on the rear is roughly half that.
Tire pressure. Under-inflated tires add rolling resistance. Check monthly; most cars lose 0.1 bar per month naturally.
Terrain. Mountainous routes and heavy stop-and-go city driving can add 30–50% over steady highway cruising.
Ambient temperature. Cold weather thickens oil and engages heaters; consumption in winter can be 10–20% higher than summer for the same route.

Worked example: road trip vs. train

A 600 km trip for three adults, Tallinn to Riga and back (so 600 km total):

Car: 6.0 L/100 km diesel, €1.85/L → (600 / 100) × 6.0 × 1.85 = €66.60. Split three ways: €22.20 per person.
Bus: Typical round-trip ticket ≈ €35 per person. €105 total.
Train (where available): varies by route.

In this case the car is cheaper per person; with only one passenger it would be more expensive than the bus.

Worked example: diesel SUV vs. petrol hatchback commute

Same 30 km round-trip commute, 220 working days per year (6,600 km/year):

Diesel SUV at 7.5 L/100 km, diesel €1.75: 66 × 7.5 × 1.75 = €866
Petrol hatchback at 5.5 L/100 km, petrol €1.80: 66 × 5.5 × 1.80 = €653
EV at 17 kWh/100 km, home electricity €0.18/kWh: 66 × 17 × 0.18 = €202

The SUV vs. hatchback gap is €213/year — noticeable but not decisive. The SUV vs. EV gap is over €600/year and compounds with lower servicing costs.

How to use this tool

Pick your units (metric or imperial).
Enter the distance in km or miles.
Enter your car’s fuel efficiency (L/100 km or MPG).
Enter the current fuel price per litre or gallon.
Optionally enter the number of passengers to split the cost.

Tips to lower real-world consumption

Keep tires at the door-sticker pressure. 0.5 bar below the recommended value can cost 3–5% fuel.
Remove roof boxes and bike racks when not in use. Drag starts to dominate above 80 km/h.
Use cruise control on flat motorway. Humans are worse than cruise at keeping a steady speed.
Don’t idle. Thirty seconds of idling uses more fuel than restarting a modern engine.
Plan fewer trips. Three errands combined into one loop consume less fuel than three cold-start trips, because the engine warms once instead of three times.
Weight and drag scale nonlinearly. At highway speeds, cleaning out the car and closing the windows can pay off more than mild driving-style changes.

Frequently asked questions

My real MPG is much worse than the sticker. Is my car broken?

Usually not. The gap between official figures and real-world consumption is standard — typically 10–20% for WLTP, up to 40% for the older NEDC cycle. If your figure is worsening steadily over months, consider a service (tire pressure, air filter, spark plugs, fuel injectors).

Diesel or petrol — which is cheaper to run?

Diesel engines are usually 15–25% more efficient per litre, but diesel is often priced a similar amount higher at the pump. At similar prices, diesel wins on high-mileage highway driving; petrol can win on short urban trips where a diesel never warms up. For new purchases in Europe, EVs now undercut both on operating cost in most countries.

How do I compare an EV to a petrol car?

Convert the EV’s kWh/100 km to a “cost per 100 km” using your electricity price, and compare directly to the petrol car’s L/100 km × fuel price. An EV at 17 kWh/100 km on €0.18 home electricity costs €3.06 per 100 km; a petrol car at 6 L/100 km on €1.80 costs €10.80 per 100 km — roughly 3.5× more.

Does this tool account for tolls and parking?

No — it covers fuel only. For a full trip-cost picture, add tolls, parking, and any vignette or congestion charges separately.

How accurate is the passenger-split figure?

It is a straight division of total fuel cost by the number of occupants. In practice you’d factor in any added load (passengers and luggage add weight, which costs fuel), but the effect is small: even a fully loaded car adds maybe 5% to consumption.

Privacy note

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Car Fuel Cost Calculator