Personal Finance
Fuel Cost Calculator
Enter trip distance, fuel economy and fuel price to see litres (or gallons) and cost.
Trip fuel cost
Use the economy your car actually achieves, not the brochure figure. Real-world mpg or L/100km is usually worse in towns, on short trips and with a roof box. Enter distance, economy and fuel price for a trip cost estimate before a weekend away or a delivery round. Price boards change weekly; use the pump price you will actually pay. Extend to full driving cost with cost per mile or compare modes with car vs train. Commute patterns sit on commute cost. For EVs, think in kWh per mile and your electricity unit rate instead of liquid fuel. Estimates only. Motorway versus urban loops can differ by double-digit percentages on the same car; keep two economy figures if your trips split that way. Roof boxes, bike racks and heavy tools in the boot deserve a worse mpg assumption. Shop around on price boards, but include the detour miles or the ‘cheaper’ forecourt loses on total cash.
Worked example
A 180-mile motorway trip in a car averaging 45 mpg (about 6.3 L/100km) with petrol at £1.45/litre uses roughly 11.3 litres → about £16.40 one way. At a realistic 38 mpg with traffic and a loaded boot, fuel rises toward £19.50 — brochure optimism is expensive.
Limits and assumptions
Ignores parking, tolls and wear. Cold starts and short hops worsen economy versus steady cruising. Not a carbon-footprint certificate.
Frequently asked questions
Should I use mpg or L/100km?
Match the unit your car’s computer reports and the mode the form expects. Do not mix without converting.
Why is my trip dearer than the estimate?
Cold starts, roof boxes, hills and heavy traffic worsen economy versus a steady motorway figure.
Does this include electric vehicles?
For EVs, think in kWh/mile and electricity unit rate instead of liquid fuel — or use the appliance-style energy maths.
How do I convert mpg to L/100km?
L/100km ≈ 282.48 ÷ mpg (UK gallon). Keep one system for the whole calculation.
Should I include detours for cheaper fuel?
Add the extra miles into distance; a long detour can erase the pence-per-litre saving.