Fuel Cost Calculator: How to Work Out Gas Mileage, Trip Cost & Fuel Efficiency (2025 Guide)
Fuel prices move up and down, but one thing never changes: nobody likes surprises at the pump. Whether you’re planning a family road trip, running weekly errands, driving for work, or managing a small business fleet, knowing the real cost of every journey helps you budget with confidence. That’s exactly what this fuel cost calculator is built for – a simple way to turn distance, fuel efficiency and fuel price into clear numbers you can actually use.
Instead of guessing, you can see in seconds how much fuel you’ll burn, how much the trip will cost, and how those costs add up over a month or year. If you’re comparing two different cars, thinking about buying something more efficient, or deciding whether a long commute is really worth it, these numbers make the decision much easier. You can even combine the results with tools like our Mortgage Calculator or Percentage Calculator when you’re planning bigger life changes that affect your overall budget.
Understanding MPG vs L/100km (and why both matter)
Different countries measure fuel efficiency in different ways, but they’re really talking about the same thing. In places like the US and UK, you’ll often see MPG (miles per gallon). The higher the number, the better: 35 MPG means the car can travel 35 miles on one gallon of fuel. In most of Europe and other regions, you’ll see L/100km (liters per 100 kilometers). Here, lower is better: 6 L/100km means the car uses 6 liters of fuel to travel 100 km.
MPG (Imperial)
MPG = Distance traveled (miles) ÷ Fuel used (gallons)
L/100km (Metric)
L/100km = (Fuel used (liters) ÷ Distance (km)) × 100
Convert MPG ⇄ L/100km
L/100km = 235.214 ÷ MPG
MPG = 235.214 ÷ L/100km
Real-world fuel efficiency is usually a bit lower than the “official” numbers in brochures, because those are measured in ideal test conditions. That’s why it’s helpful to use your own real figures when you can – for example from your car’s trip computer or from fuel receipts. The closer the MPG or L/100km value is to what you actually get on the road, the closer your trip cost estimate will be to reality.
How to calculate fuel cost for any trip (with simple examples)
Under the hood, the calculator is using straightforward formulas. Once you understand the logic, you can check the numbers yourself and trust what you see on the screen. You only need three things: distance, fuel efficiency and fuel price. The calculator then shows fuel needed, total cost and cost per mile or kilometer.
Trip distance: 450 miles
Fuel efficiency: 30 MPG
Fuel price: $3.60 per gallon
Fuel needed = Distance ÷ MPG = 450 ÷ 30 = 15 gallons
Total cost = Fuel needed × Price = 15 × 3.60 = $54.00
Cost per mile = Total cost ÷ Distance = 54 ÷ 450 ≈ $0.12 per mile
Trip distance: 700 km
Fuel consumption: 7.5 L/100km
Fuel price: €1.70 per liter
Fuel needed = (Distance × L/100km) ÷ 100 = (700 × 7.5) ÷ 100 = 52.5 liters
Total cost = Fuel needed × Price = 52.5 × 1.70 = €89.25
Cost per km = Total cost ÷ Distance = 89.25 ÷ 700 ≈ €0.13 per km
Instead of doing this math by hand every time, the fuel cost calculator does it instantly for you and then goes one step further: it shows a round-trip estimate, plus a rough monthly and yearly cost if you make the same journey regularly. That’s extremely useful when you’re thinking about a new job with a longer commute or comparing two possible routes to the same destination.
If you drive for work, freelance, deliver goods or manage a small fleet, these numbers can feed directly into your prices and day rates. You can also save your results in CSV format and open them in a spreadsheet alongside other costs such as insurance, tolls and maintenance. For more complex planning you can pair this with tools like our Auto Loan Calculator or Loan Calculator to see the full cost of owning and running a vehicle.
Simple ways to reduce fuel cost without changing your car
A more efficient car is great, but you don’t always need a new vehicle to start saving. Small changes to how you drive and maintain your current car can make a noticeable difference. Once you’ve used the calculator, try adjusting the MPG or L/100km value to see how a small improvement affects your yearly fuel cost – it’s often more than people expect.
- Drive smoothly: harsh acceleration and heavy braking can easily waste 10–20% more fuel. Gentle inputs and looking further ahead help a lot.
- Stick to sensible speeds: most cars are much more efficient at moderate highway speeds. Jumping from 60 mph to 75 mph can increase fuel usage significantly.
- Check tire pressures monthly: soft tires create extra drag and can quietly eat into your MPG. Proper pressure also makes the car feel nicer to drive.
- Lighten the load: roof boxes, bike racks and “just in case” heavy items in the boot all make your car work harder than it needs to.
- Combine short trips: engines use more fuel when cold. Doing one longer errand run instead of several very short trips can reduce overall consumption.
As you tweak these habits, you can come back to this page and plug in better MPG or L/100km figures to see how much you are actually saving over the year. If you’re tracking other areas of your health and finances, you might also like our BMI Calculator and Budget Calculator to keep everything in one place.
In short, this fuel cost calculator turns confusing fuel bills into clear, simple numbers. Once you see what each journey really costs, you can make better decisions about how often you drive, which routes you choose and which vehicle you rely on the most. Over time, those small decisions add up to serious savings.
Fuel Cost Calculator – Frequently Asked Questions
1. How do I calculate fuel cost for a road trip?
Enter the total distance of your trip, your car’s fuel efficiency (MPG or L/100km) and the fuel price per gallon or liter. The calculator will instantly show you how much fuel you’ll use and the total cost. You can also see cost per mile or kilometer and a round-trip estimate.
2. What information do I need to use the fuel cost calculator?
You only need three things: distance, fuel efficiency and fuel price. If you don’t know your exact MPG or L/100km yet, you can start with an estimate from your car’s manual and refine it later using your real usage.
3. What if I do not know my car’s MPG or L/100km?
You can estimate it by filling the tank, resetting your trip counter, driving as normal and then dividing the distance you drove by the fuel you used. Most modern cars also show average fuel economy on the dashboard, which you can use directly in the calculator.
4. Can I use this fuel cost calculator for diesel, LPG or other fuels?
Yes. The calculator works with any road fuel. Just use the correct fuel price per gallon or liter and enter the correct MPG or L/100km for that fuel type. The formulas behind the calculator are the same.
5. How do I work out cost per mile or cost per kilometer?
The calculator shows this automatically. Cost per mile is fuel price divided by MPG. Cost per kilometer is fuel price multiplied by L/100km and divided by 100. This is a useful number when you want to compare different routes or see how much regular commuting really costs.
6. Is this fuel cost calculator accurate enough for business mileage and budgeting?
For most people, yes. As long as your distance, fuel efficiency and fuel price are realistic, the results are accurate enough for personal budgeting, quotes and basic business planning. For official mileage claims, always follow the rules from your local tax authority.
7. Does the calculator support both one-way and round trips?
The main calculation is for one direction, but the results section includes a round-trip breakdown and a simple estimate of what you would spend monthly or yearly if you repeat the same trip regularly.
8. How can I reduce my fuel costs using the results?
Try changing the MPG or L/100km value to see how better driving habits, lighter loads or a more efficient car affect the yearly cost. You can also experiment with different distances to compare routes, or check whether carpooling might make more sense for longer trips.