What will the fuel cost?

We find the two places on the map (postcodes through postcodes.io, towns and villages from OS Open Names). Then we ask a route finder built on OpenStreetMap (OSRM) for the driving route. So the distance is the real road distance, not a straight line. If the route finder is down, we use the straight-line distance plus 25%, and we tell you that is what we did.

The DVLA's Vehicle Enquiry Service gives us the make, fuel type, engine size, year and official CO2 figure for a registration. It does not give the model or the mpg. But every gram of CO2 per km means a fixed amount of fuel was burned (2,392 g per litre of petrol, 2,640 g per litre of diesel), so we can work out the official mpg from the CO2 figure. We take 10% off to allow for real-world driving. Older vehicles and most motorbikes have no CO2 figure on record, so they get a typical figure for their engine size. You can type over the number if you know better. The lookup is not switched on on this server yet, so use the picker or type your mpg.

At today's average petrol price of –, a car doing 45 mpg costs about 17p a mile in fuel. To work it out yourself: divide the miles by your mpg to get gallons, multiply by 4.546 to get litres, then multiply by the price in pence per litre and divide by 100 to get pounds. A 200-mile trip at 45 mpg uses 4.4 gallons, which is 20.2 litres, and costs –.

A typical family car has a tank of 45 to 60 litres (10 to 13 gallons). At today's UK average petrol price of –, filling a 50-litre tank from empty costs –. Diesel at – costs –. At the cheapest forecourt in the country (–) it would cost –.