Fuel Cost Calculator
Before a road trip you want to know what the fuel will cost. This calculator handles every common combination of units — kilometres or miles, km per litre, litres per 100 km, miles per US gallon or UK gallon, and prices per litre or gallon — so a US driver, a UK driver and an Indian driver can all use it. It works out the fuel needed, the total cost, the cost per kilometre and per mile, each person’s share and an estimate of the CO₂ produced, using the U.S. EPA’s emission factors.
How to use the fuel cost calculator
- Enter the trip distance and choose kilometres or miles; tick round trip if you are coming back.
- Enter your vehicle’s fuel efficiency and choose its unit. Real-world efficiency is usually lower than the brochure figure.
- Enter the fuel price and its unit, and how many people share the cost.
- Read the total cost, cost per person, cost per km or mile and CO₂.
Formula
Fuel (litres) = distance ÷ efficiency in km per litre, or distance × L/100km ÷ 100. For miles per gallon, gallons = miles ÷ mpg, with 1 US gallon = 3.7854 L and 1 UK gallon = 4.5461 L. Cost = fuel × price per litre. CO₂ uses the EPA factors of 8,887 g per US gallon of gasoline and 10,180 g per US gallon of diesel.
Worked examples
A 300 km round trip in India
A 300 km return trip (600 km) at 15 km/l with petrol at ₹100 a litre uses 40 litres (10.57 US gal · 8.799 UK gal) and costs ₹4,000.00 — ₹2,000.00 each between two people, or ₹6.67 a kilometre.
A US road trip
A 300-mile round trip (600 miles) at 30 mpg with gasoline at $3.50 a US gallon costs $70.00, producing about 177.7 kg of CO₂.
Same efficiency, three units
A car that does 15 km/l is the same as 6.67 litres per 100 km, or about 35.3 miles per US gallon (42.4 miles per UK gallon) — the calculator converts between them automatically.
Practice problems
Try these yourself first, then check your answer. The answers come from the calculator above.
- A 450 km one-way trip at 18 km/l with petrol at ₹105 a litre. What is the fuel cost?
Show answer
Total fuel cost: ₹2,625.00
Common mistakes to avoid
- Using brochure mileage. Traffic, load, speed and air conditioning lower real-world efficiency.
- Mixing US and UK gallons. A UK gallon is about 20% larger.
- Forgetting the return journey.
- Ignoring tolls, parking and wear and tear.
- Entering mpg when the field expects km/l (check the unit selector).
Frequently asked questions
How do I calculate fuel cost for a trip?
Divide the distance by your vehicle’s efficiency to get the fuel needed, then multiply by the price per unit of fuel.
How do I convert km/l to L/100km?
Divide 100 by km/l. 15 km/l is 6.67 L/100km.
How do I convert mpg to km/l?
Multiply US mpg by 0.4251 to get km/l (UK mpg by 0.3540).
How accurate is the CO₂ figure?
It uses the EPA’s standard emission factor per gallon of fuel burnt; it covers tailpipe CO₂ only.
Does this include tolls?
No — only fuel.
Sources and further reading
- U.S. EPA — Greenhouse gas equivalencies: calculations and references (CO₂ per gallon of fuel)
- U.S. Department of Energy — FuelEconomy.gov
Reviewed September 26, 2026 by the SolveCalcPro editorial team. Found a mistake? Tell us; see our editorial policy.