Breakdown
How it works
Litres used = distance ÷ economy (or distance × L/100km ÷ 100). Multiply by price per litre. Real-world consumption is typically 10–20% worse than the official figure, more in city traffic and with air-conditioning in Gulf summers.
Formula
Litres = km ÷ (km/L) = km × (L/100km) ÷ 100 = miles ÷ mpg × 4.546
Cost = litres × price per litre
Worked example
300 km at 12 km/L and 2.00 per litre: 25 litres, 50.00. Two people: 25.00 each.
Frequently asked questions
How do I convert mpg to L/100km?
L/100km = 282.5 ÷ UK mpg (235.2 ÷ US mpg). 40 UK mpg = 7.1 L/100km = 14.2 km/L.
What is a fair fuel contribution for a lift?
Fuel cost per person plus a share of wear: HMRC allows 45p a mile (25p after 10,000) as the full running cost in the UK; fuel alone is roughly 12–16p a mile.
Petrol vs electric cost per km?
A petrol car at 14 km/L and 2.00/L costs 0.14 per km; an EV at 6 km/kWh charged at 0.30/kWh costs 0.05 per km. Public rapid charging at 0.80/kWh narrows the gap.