Fuel Cost Calculator
Estimate trip fuel costs or find your real consumption
Fuel needed
L
Total cost
Cost per km
Per person
Actual consumption
L/100km
MPG (US)
How to Use
- Pick a mode — “Trip estimate” plans fuel costs before a journey; “Actual efficiency” reads your real consumption after a fill-up.
- Choose your units — metric (km, L/100km, price per litre) or US (miles, MPG, price per gallon). The English page starts in US units.
- Enter the numbers — trip mode asks for distance, efficiency, fuel price, and how many people share the cost. Actual mode asks only for distance driven and fuel used.
- Read the results — trip mode reports fuel needed, total cost, cost per km or mile, and cost per person. Actual mode reports consumption in both L/100km and MPG at once.
The Formulas Behind Each Result
The math depends on the unit system, because the two efficiency conventions are inverses of each other.
| Quantity | Metric | US |
|---|---|---|
| Fuel needed | distance ÷ 100 × L/100km | distance ÷ MPG |
| Total cost | fuel × price per litre | fuel × price per gallon |
| Cost per unit distance | total ÷ distance | total ÷ distance |
| Per person | total ÷ people | total ÷ people |
| Actual consumption | fuel used ÷ distance × 100 | distance ÷ fuel used (MPG) |
The conversion constant is (100 × 3.785411784) ÷ 1.609344 ≈ 235.2145833, where 3.785411784 is the litres in a US gallon and 1.609344 is the kilometres in a mile. Multiplying any consumption in L/100km by the same consumption in MPG gives that constant.
Worked Examples in Both Unit Systems
Metric trip. A 500 km drive in a car using 7 L/100km, fuel at 1.80 per litre, four people sharing. Fuel is 500 ÷ 100 × 7 = 35 L; total cost is 35 × 1.80 = 63.00; cost per km is 63 ÷ 500 = 0.126; per person is 63 ÷ 4 = 15.75.
US trip. A 300-mile drive at 30 MPG, fuel at 3.50 per gallon, two people. Fuel is 300 ÷ 30 = 10 gal; total cost is 10 × 3.50 = 35.00; cost per mile is about 0.12; per person is 17.50.
Actual efficiency. If you drive 500 km and refill with 40 litres, consumption is 40 ÷ 500 × 100 = 8 L/100km, which the tool also reports as about 29.4 MPG. In US units, 300 miles on 10 gallons gives 30 MPG, also shown as about 7.8 L/100km.
Why L/100km and MPG Move in Opposite Directions
This is the single most common source of confusion when comparing cars across regions. L/100km tells you how much fuel an engine drinks to cover a fixed distance, so smaller is better. MPG tells you how far a fixed amount of fuel takes you, so larger is better. A car rated 5 L/100km is efficient; a car rated 25 L/100km is not, even though 25 sounds like a bigger and therefore “better” number. Because the relationship is inverse, improvements are not linear: going from 10 to 8 L/100km saves more fuel per kilometre than going from 6 to 5. The unit buttons let you see both readings for the same fill-up so the comparison is unambiguous.
Common Mistakes
- Mixing US and imperial gallons. The calculator uses US gallons. An imperial (UK) MPG figure is roughly 20% higher for the same real consumption, so do not paste a UK figure into the US mode.
- Using the brochure number for a trip estimate. Manufacturer figures are measured on a test cycle. For budgeting, use the actual-efficiency mode across several tanks to get a realistic figure.
- Splitting cost by people before adding tolls and parking. The tool counts fuel only. Add non-fuel costs separately, then divide.
- Forgetting to reset the trip odometer. The actual mode asks for distance since the last fill-up; if you forget to reset, the reading is wrong.
- Assuming switching units converts your inputs. It does not; re-enter the values.
What the Calculator Leaves Out
Fuel cost is only part of running a car. Depreciation, insurance, maintenance, tyres, and tolls are not included, and EV energy use is out of scope by design. The tool also assumes a steady consumption rate for the whole trip; a route that is mostly uphill, heavily loaded, or stuck in traffic will burn more than the estimate. Use the result as a planning baseline and adjust with your own real-world numbers.
Planning a Road Trip with the Numbers
The trip mode is most useful when you run it a few times with different assumptions. Start with the manufacturer figure for a rough floor, then repeat with your real-world consumption from the actual-efficiency mode; the gap between the two is usually the difference between a comfortable budget and a surprise at the pump. Add a margin for detours, idling in traffic, and air-conditioning, all of which raise consumption above a steady-cruise figure. If the trip crosses regions with different fuel taxes, split the route into legs and price each one separately, since a long highway stretch at cheap rural prices can be cheaper than filling up before you leave. Finally, remember that range matters as much as cost: a car that needs two refills on a remote route may be a worse choice than a slightly thirstier one that can do it in one tank.
Related Tools
- Tip Calculator — split restaurant bills the same way you split fuel costs.
- Discount Calculator — work out sale prices and savings.
- Unit Converter — convert between other measurement units.
Frequently Asked Questions
In which unit system does the calculator open in English?
The English page defaults to US units — miles, MPG, and price per gallon — with sample values of 300 miles, 30 MPG, and 3.50 per gallon. The Chinese and German pages default to metric. You can switch at any time with the unit buttons.
When I switch units, does the tool convert the numbers I typed?
No. Switching units relabels the fields and reinterprets the same numbers in the new system, so a distance of 300 becomes 300 miles or 300 kilometres rather than being converted. Re-enter values if you switch systems.
Why does 8 L/100km equal about 29.4 MPG?
L/100km and MPG measure consumption in opposite directions, and their product is a constant. With US gallons the factor is 235.2145833, so dividing it by 8 gives 29.40 MPG, and dividing it by 30 MPG gives 7.84 L/100km.
Does a higher number always mean better fuel economy?
No, and that is the trap. In MPG a higher number is better; in L/100km a lower number is better. Always check which unit you are reading before judging a figure.
Can I use this for an electric vehicle?
No. EVs use kWh per 100 km and electricity tariffs, which involve charging losses and time-of-use rates that this calculator does not model. It is limited to gasoline and diesel.
What happens if I enter zero people to split the cost?
The calculator rejects it. The people field must be a whole number of at least 1, so the trip results hide and an invalid-input hint appears. Fuel price, however, may be zero, which is useful for a free or reimbursed fill-up.
Reviewed by the HandyTools Hub team · Last updated