Automotive calculators

Fuel economy is quoted two opposite ways — distance per fuel and fuel per distance — and mixing them up is the commonest error. Both calculators work in either system and show the conversion between them.

Trip estimates depend on the inputs you choose. Fuel cost multiplies the distance by your car’s consumption and the price you pay per unit, so a rough consumption figure gives a rough cost. Use the number from your own last fill-up, found with the gas mileage calculator, rather than the figure on the brochure.

Travel time works the same way: distance divided by an average speed, plus the stops you plan. Motorway cruising speed is not an average, because junctions, traffic and breaks all pull the average down. Enter the average you expect for the whole journey, and add stop time separately so the arrival time stays honest.

Each calculator shows its formula and the substituted values, so you can repeat the sum by hand or with a different car, fuel price or route and see which input moves the answer most.