⛽ Fuel Cost Calculator
Trip fuel cost is simply the fuel your journey uses times the price per unit — the only trick is matching your economy units. Enter your values below — results update instantly, entirely on your device.
10 US gallons × 3.5/unit
per mile / km travelled
How the fuel cost calculator works
Fuel used = distance ÷ economy (or distance × economy ÷ 100 for L/100 km); cost = fuel used × price per unit. Keep distance and economy in the same system — miles with MPG, kilometres with L/100 km or km/L.
Example: A 300-mile trip at 30 MPG with fuel at 3.50/gallon uses 10 gallons and costs about 35.
Real-world economy runs below the sticker figure — city driving, cold starts, roof racks, heavy loads and highway speeds above ~60 mph all cut it, often 10–20%. For a trip budget, use your car's actual observed economy (fill-to-fill) rather than the rated number, and add a little headroom. Choose the units your dashboard and pump use to avoid a MPG/L-per-100 km mix-up.
Frequently asked questions
How do I calculate the fuel cost of a trip?
Work out the fuel your trip needs, then multiply by the price. For MPG: fuel = distance ÷ MPG; for L/100 km: fuel = distance × (L/100 km) ÷ 100. A 300-mile trip at 30 MPG uses 10 gallons — times the pump price gives the cost.
What's the difference between US and UK MPG?
The gallon. A US gallon is 3.785 litres and an imperial (UK) gallon is 4.546 litres — about 20% larger — so the same car reads a higher MPG in UK figures. Pick the right one, or your estimate will be off by a fifth.
How do I convert L/100 km to MPG?
They're inverse measures: MPG (US) ≈ 235.2 ÷ (L/100 km). So 8 L/100 km ≈ 29 MPG. This calculator lets you just pick your unit instead of converting by hand.
Why is my real fuel economy worse than the rating?
Official figures come from controlled tests. Real driving adds cold starts, city stop-go, high speeds, air conditioning, cargo and terrain — commonly cutting economy 10–20%. Use your own fill-to-fill average for trip budgeting.
Is this fuel cost calculator accurate and private?
Yes. It uses the standard published formula, shows its working under every result, and computes locally in your browser — your inputs are never sent to a server, and the page works offline.