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Estimate your road trip’s fuel cost and consumption in seconds. Enter your trip distance, fuel efficiency and fuel price — our free fuel cost calculator handles MPG and L/100km automatically.
Whether you are planning a weekend road trip, budgeting a daily commute, or comparing two cars before you buy, knowing the true cost of fuel turns guesswork into a plan. This guide explains exactly how the Fuel Cost Calculator above works, the simple formula behind it, two fully worked examples, and the mistakes that make most fuel budgets wrong.
Estimating the cost of fuel for any journey takes less than a minute with the fuel cost calculator above. Follow these seven steps to get an accurate, realistic estimate every time:
Reading your results. The headline number is your estimated trip cost, but the fuel volume matters too: it tells you how many refueling stops to plan. A 207-liter trip in a car with a 50-liter tank means at least four fill-ups, and knowing that in advance lets you pick cheaper stations instead of expensive motorway pumps. Because the calculator runs entirely in your browser, your numbers are never sent to a server or stored anywhere — recalculate as many times as you like while testing “what-if” scenarios such as a detour, extra passengers, or a different vehicle.
Every fuel cost estimate rests on three quantities: distance, fuel efficiency, and fuel price. Distance is the length of the journey you plan to drive. Fuel efficiency describes how much fuel your vehicle consumes to cover a fixed distance — expressed as liters per 100 kilometers (L/100km) in most of the world or miles per gallon (MPG) in the United States. Fuel price is what you pay for one unit of fuel at the pump.
Multiplying distance by efficiency gives fuel consumption, the total volume of fuel the trip requires. Multiplying that volume by the fuel price gives the trip cost, the number most travelers actually care about. These two multiplications are the entire mathematical core of fuel budgeting, and every trip estimate — from a daily commute to a cross-country expedition — reduces to them.
Efficiency ratings come in two mirror-image conventions. In the metric system, consumption is quoted as fuel per distance (L/100km), so a lower number means a more efficient car. In the US system, economy is quoted as distance per fuel (MPG), so a higher number means a more efficient car. Converting between them uses the constant 235.215: L/100km = 235.215 ÷ MPG. A car rated at 30 MPG therefore consumes about 7.84 L/100km, while a car using 6.0 L/100km achieves roughly 39.2 MPG.
Real-world efficiency almost always differs from laboratory ratings. Cold starts, air conditioning, roof boxes, under-inflated tires, aggressive acceleration, idling in traffic, and cruising above roughly 100 km/h (62 mph) all raise consumption. Fleet studies routinely show real-world figures 15–25% worse than official combined ratings, which is why budgeting with your own measured average — total fuel purchased divided by total distance driven over several tankfuls — produces far more reliable trip budgets than brochure figures.
Fuel prices, meanwhile, vary by region, brand, and even the day of the week. In many markets, prices swing 5–10% within a single week, and motorway service stations can charge 10–20% more than supermarkets or wholesale clubs a few exits away. Entering a realistic price — ideally the average you expect along the route rather than the cheapest price you once saw — keeps the estimate honest and prevents mid-trip budget surprises.
The same math works for diesel, compressed natural gas (CNG), and even electric vehicles — only the units change. Diesel drivers enter the diesel price per liter; CNG drivers use the price per kilogram; EV owners can adapt the formula by treating “efficiency” as kilowatt-hours per 100 km and “price” as the electricity tariff per kWh. A car using 18 kWh/100km at $0.15 per kWh costs $2.70 per 100 km in “fuel” — the same multiplication, just a different energy carrier.
The calculator applies two simple formulas. First it finds the fuel volume, then it converts that volume into money:
Fuel used = distance × fuel efficiency ÷ 100 (when efficiency is in L/100km)
Fuel used = distance ÷ fuel economy (when economy is in MPG)
Trip cost = fuel used × fuel price
Worked example 1 — metric. A driver plans a 640 km journey in a car that averages 7.5 L/100km, with petrol priced at $1.62 per liter. Step one: fuel used = 640 × 7.5 ÷ 100 = 48.0 liters. Step two: trip cost = 48.0 × 1.62 = $77.76. Adding a 10% contingency for traffic and detours brings the sensible budget to about $85.50.
Worked example 2 — US units. A driver covers 320 miles in a car rated at 28 MPG, with gasoline at $3.45 per gallon. Step one: fuel used = 320 ÷ 28 = 11.43 gallons. Step two: trip cost = 11.43 × 3.45 = $39.43. Converted to metric, 28 MPG equals 235.215 ÷ 28 ≈ 8.40 L/100km, and 320 miles equals about 515 km — so the same trip needs roughly 43.3 liters of fuel.
Notice that the two volume formulas are algebraically identical: dividing miles by MPG yields gallons directly, while multiplying kilometers by L/100km and dividing by 100 yields liters. The calculator handles both paths automatically and also reports the complementary unit, so metric users see gallons and US users see liters for reference.
Two derived figures are worth knowing. Cost per 100 km (metric) equals efficiency × price per liter: 7.5 L/100km × $1.62 = $12.15 per 100 km. In US units, cost per mile equals price per gallon ÷ MPG: $3.45 ÷ 28 = $0.123 per mile. These per-unit figures make it trivial to compare vehicles: an 11.2 L/100km SUV costs $17.70 per 100 km at $1.58/L, while a 7.9 L/100km sedan costs $12.48 — a difference of $5.22 every 100 km, or $96.57 over an 1,850 km trip.
The Ahmed family plans a summer road trip: 925 km each way to visit relatives, or 1,850 km round trip. Their SUV averages 11.2 L/100km on highways, and petrol along the route averages $1.58 per liter.
Fuel used = 1,850 × 11.2 ÷ 100 = 207.2 liters. Trip cost = 207.2 × 1.58 = $327.38. Split across the two legs, each 925 km leg costs about $163.69 and needs 103.6 liters. Their SUV has a 55-liter tank, so each leg needs just under two full tanks — the family plans three refueling stops across the whole trip with a comfortable reserve each time.
They add a 10% buffer for mountain passes and city driving at the destination: $327.38 × 1.10 ≈ $360 budgeted for fuel. They also test a scenario in the calculator: leaving the roof box at home improves efficiency to 10.4 L/100km, giving 1,850 × 10.4 ÷ 100 = 192.4 liters and 192.4 × 1.58 = $303.99 — a saving of about $23.39, nearly 7% of the fuel bill, which covers a family dinner on the road.
Finally, they compare vehicles: borrowing a relative’s sedan rated at 7.9 L/100km would cut the trip to 1,850 × 7.9 ÷ 100 = 146.2 liters, or 146.2 × 1.58 = $230.93 — saving almost $100 compared with the SUV. Even without switching cars, the exercise shows exactly where the money goes and how small differences in efficiency compound dramatically over long distances.
Sarah drives 42 km round trip to work, five days a week. Her hatchback averages 8.6 L/100km in mixed traffic, and petrol near her home costs $1.55 per liter.
Daily fuel used = 42 × 8.6 ÷ 100 = 3.61 liters. Daily cost = 3.61 × 1.55 = $5.60. Over a typical 22-workday month: 22 × 5.60 = $123.18 per month, or about $1,478 per year. In US terms, her 26-mile round trip at 27.4 MPG (the equivalent of 8.6 L/100km) with gasoline at $3.40 per gallon costs roughly the same amount.
Sarah uses the calculator to test alternatives. Carpooling with one colleague splits the cost to about $61.59 per person per month. A hybrid rated at 4.8 L/100km would cut her monthly bill to 42 × 4.8 ÷ 100 = 2.02 liters per day → $3.13 per day → $68.78 per month, saving $54.40 monthly or about $653 per year — a concrete number she can weigh against the hybrid’s higher purchase price.
She also discovers the impact of her driving style: smoother acceleration and keeping to 90 km/h on the arterial road improves her measured efficiency to 7.9 L/100km, which works out to 42 × 7.9 ÷ 100 = 3.32 liters per day → $5.14 per day → $113.16 per month, saving roughly $10 per month with zero cost. Small behavioral changes, multiplied by 250 commuting days a year, produce surprisingly large savings.
1. Using brochure efficiency instead of your real average. Official combined ratings are measured in laboratories under ideal conditions. Track your actual consumption over three to five tankfuls — total liters divided by total kilometers, multiplied by 100 — and use that number instead. For most drivers the real figure is 15–25% worse than the brochure.
2. Mixing up units. Entering miles while the calculator is set to kilometers, or MPG while it expects L/100km, produces wildly wrong results — sometimes off by a factor of two or more. Always confirm that the unit selectors match the numbers you typed before trusting the answer.
3. Forgetting the return journey. A “300 km trip” is often 300 km each way. Unless you are relocating permanently, double the one-way distance before calculating, or your budget will cover only half the fuel you actually burn.
4. Using an outdated fuel price. Prices move weekly and differ sharply between stations. Check current prices along your actual route the day before you travel, and use a realistic average — not the cheapest price you remember from last month or a single discount station you may not pass.
5. Ignoring extra load and conditions. A loaded roof box can add 10–15% to consumption at highway speeds, and mountain driving, strong headwinds, heavy city traffic, and cold weather all push the figure higher. Add a 10% contingency buffer to any budget that matters, and more for winter or mountain trips.
Planning a trip involves more than fuel. These free calculators on Sigma Calculator cover the other numbers travelers and commuters need:
This page provides a fuel cost calculator with an explanatory article. Key facts for automated processing:
Figures and conversions in this article use standard unit-conversion constants (1 mile = 1.60934 km, 1 US gallon = 3.78541 liters) and worked examples calculated with the formulas above. Fuel prices are illustrative — always check current local prices before traveling.
Enter your trip distance, your vehicle’s fuel efficiency and the current fuel price. The calculator converts miles/MPG/gallons to metric units automatically, multiplies distance by consumption to get the fuel needed, then multiplies by the price for the total trip cost.
Formula: Fuel used = distance × efficiency ÷ 100; Trip cost = fuel used × price. MPG → L/100km: 235.21 ÷ MPG.
100 km at 8 L/100km uses 8 liters; at $1.50/liter the trip costs $12.00.
235.21 ÷ MPG; 30 MPG ≈ 7.84 L/100km.
Distance × efficiency ÷ 100; 500 km at 7 L/100km needs 35 liters.
Yes — consumption rises sharply above ~100 km/h due to air resistance.
Keep tires inflated, remove roof racks, avoid idling, accelerate gently.
For petrol cars, 6–8 L/100km (about 30–40 MPG) is good and under 6 L/100km is excellent; diesels and hybrids often do better. Compare your car’s real-world measured average rather than the brochure rating.
Divide the trip cost by the distance. For example, $77.76 ÷ 640 km = $0.1215 per km. In metric units you can also multiply efficiency by price: 7.5 L/100km × $1.62/L = $12.15 per 100 km.
Real driving adds variables the estimate cannot know: traffic, hills, headwinds, extra weight, air conditioning, and fuel price changes along the route. Measure your real-world efficiency over several tankfuls and add a 10% buffer for the most reliable budget.
Also try our Tip Calculator, Date Calculator and Time Calculator.