Gas cost and fuel economy calculator

How much will the trip cost in gas? Enter distance, your car's mpg and the price per gallon — and convert fuel economy to any unit.

Free, no sign-up

Before you use it

Works well for

  • Road trip fuel cost and splitting it with passengers
  • Converting mpg, L/100 km and km/L
  • Comparing cars by running cost

Not the right tool for

  • Electric or plug-in hybrid driving
  • Exact consumption — it depends on speed, load and traffic

How it works

Gallons needed = miles ÷ mpg, and cost = gallons × price per gallon. A 300-mile trip in a 28 mpg car uses 10.7 gallons; at $3.40 a gallon that's about $36. Tick "round trip" to double the distance, and add tolls and parking to get the full cost to split.

Converting fuel economy

  • mpg (US) uses the 3.785-liter US gallon.
  • mpg (UK) uses the 4.546-liter imperial gallon, so the same car shows a higher number in the UK.
  • L/100 km is used in Europe, Canada and Australia — lower is better.
  • km/L is common in Latin America and parts of Asia.

Quick reference: 30 mpg (US) ≈ 7.8 L/100 km; 10 L/100 km ≈ 23.5 mpg (US).

Frequently asked questions

Why does my car use more than its rated mpg?

Highway speed, air conditioning, cargo, tire pressure and traffic all change real economy. Use your own average from the trip computer for the best estimate.

Does it work for electric cars?

Not directly — it's built for liquid fuel. For EVs, multiply kWh per 100 miles by distance and the electricity price.

Can I use kilometers and liters?

Yes. Pick km for distance, any economy unit, and price per liter.