Fuel Cost Calculator — Road Trip Gas Cost
Enter your trip distance, fuel economy, and current gas price to calculate the exact fuel cost for any journey. Supports US (MPG/gallons), UK (MPG/litres), and metric (L/100km) units. No signup, runs entirely in your browser.
How the Fuel Cost Calculator Works
- 1Select your unit system — US (miles and gallons), UK (miles and litres), or metric (km and L/100km).
- 2Enter the trip distance in miles or kilometres.
- 3Enter your vehicle's fuel economy — MPG from the dashboard or owner's manual, or L/100km for metric vehicles.
- 4Enter the current fuel price per gallon or litre, and the number of trips if calculating a round trip or commute total.
MPG vs L/100km — Which Fuel Economy Measure Is More Useful?
MPG (miles per gallon) is intuitive — bigger is better. But it is non-linear, which means the fuel saving from going from 15 to 20 MPG is much larger than going from 40 to 50 MPG, even though both are 5 MPG improvements. L/100km (litres per 100 km) is linear and proportional — halving L/100km always halves fuel cost. For comparing vehicles with very different efficiency levels, L/100km gives a clearer picture of real-world saving.
Tips for Reducing Fuel Costs
Drive at optimal speed
Fuel efficiency peaks for most cars between 45–55 mph (70–90 km/h). Highway driving above 70 mph can reduce MPG by 15–20%. On long trips, using cruise control in this range saves meaningfully over hours.
Check tyre pressure before a trip
Under-inflated tyres increase rolling resistance. Each 10 PSI below recommended pressure reduces MPG by roughly 0.5–1%. On a long trip, properly inflated tyres can save 3–5% in fuel costs.
Limit air conditioning
Air conditioning reduces fuel economy by 5–25%, with the largest impact at low speeds. At highway speeds, AC has less impact than opening windows (which increases drag). Use AC on motorways; consider opening windows in town.
Use the highway MPG rating for road trips
The EPA combined MPG is weighted 55% city, 45% highway. For a mostly-highway road trip, use the highway MPG figure in the calculator for a more accurate cost estimate — combined will overestimate your actual consumption.
Compare fuel prices along the route
Gas prices can vary by 20–40 cents per gallon across a state. Apps like GasBuddy show prices at stations along your route. Filling up in lower-price areas can save several dollars on a long trip, especially with a large tank.
Calculate per-trip commute cost
Use the calculator with your daily commute distance, your car's MPG, and current gas price. Multiply by working days to see the monthly fuel cost — a useful data point when comparing public transport costs or considering a work-from-home arrangement.
Frequently Asked Questions
How is the fuel cost calculated?
For US/UK MPG: fuel (gallons) = distance ÷ MPG. For metric: fuel (litres) = distance ÷ 100 × L/100km. The fuel volume is then multiplied by the price per unit. For US mode, that is gallons × price/gallon. For UK and metric modes, it is litres × price/litre.
Where do I find my car's fuel economy rating?
In the US, fuel economy is listed on the EPA window sticker and at fueleconomy.gov. For combined city/highway driving, use the combined MPG figure. For UK vehicles, use the official combined figure in MPG. For European and other metric vehicles, use the L/100km combined figure from the manufacturer or registration documents.
Should I use city, highway, or combined MPG?
For accurate road trip calculations, use the highway MPG rating if you are driving mostly motorways or highways. Use combined MPG for a mix of urban and open road driving. Actual fuel economy can vary by 10–20% depending on speed, air conditioning, load, and road conditions.
Can I calculate cost for a return trip?
Yes — set the number of trips to 2. The total cost field will show both legs combined. For a route with different distances each way (unlikely but possible), run the calculator twice and add the results.
How do I compare fuel cost between two vehicles?
Run the calculator twice with the same distance and fuel price but different MPG or L/100km figures. The difference in the "cost per trip" result is the saving from the more efficient vehicle. This is useful for choosing between a rental car upgrade or comparing EV vs petrol running costs.
Does the calculator account for other trip costs like tolls?
No — this calculator covers fuel cost only. For a complete road trip budget, add tolls, parking, accommodation, and food separately. The fuel cost is typically the largest single controllable variable cost for a driving trip.
Does this calculator store my inputs or send data anywhere?
No. All calculations run entirely in your browser. Nothing is sent to any server.