Choose a calculator
For fuel economy, the MPG calculator works from distance and fuel used, and the fuel economy converter swaps between US mpg, imperial mpg, L/100 km and km/L. For running costs, the fuel cost calculator prices a trip or a year of driving, and the EV charging cost calculator compares charging with petrol.
For wheels and drivetrain, the tire size calculator compares two sizes and shows speedometer error, the gear ratio calculator gives engine RPM at speed, and the horsepower calculator converts torque, hp, kW and PS. The speed, distance and time calculator works out average speed and journey times.
- MPG Calculator – Miles per gallon (US and UK), L/100 km and km/L from distance and fuel.
- MPG to L/100 km Converter – US mpg, UK mpg, L/100 km and km/L, converted in one step.
- Fuel Cost Calculator – Trip and Gas Cost – Trip fuel cost from distance, economy and price, with cost per person.
- EV Charging Cost Calculator – Cost per charge, per mile, MPGe and saving versus petrol.
- Tire Size Calculator – Compare Tyre Sizes and Speedometer Error – Compare two tyre sizes: diameter, sidewall, circumference and speedometer error.
- Gear Ratio Calculator – Ratio and Engine RPM at Speed – Gear ratio from teeth, and engine RPM at speed from gears and tyre size.
- Horsepower Calculator – Torque, RPM, kW and PS – Horsepower from torque and RPM, torque from hp, and hp ↔ kW ↔ PS.
- Speed, Distance and Time Calculator – Average Speed – Average speed, distance or journey time, in mph, km/h, knots and pace.
Frequently asked questions
Why do US and UK miles per gallon differ?
The US gallon is 3.785 litres and the imperial gallon is 4.546 litres, so the same car has a higher mpg figure in the UK. 30 imperial mpg is about 25 US mpg. The calculators let you choose which gallon you mean.
What is L/100 km and how does it compare with mpg?
L/100 km is the fuel used to travel 100 km, so a lower number is better, while a higher mpg is better. The two are inversely related, which is why the converter does the maths rather than a simple multiplication.
Are fuel and charging costs exact?
They are estimates from the distance, fuel economy and price you enter. Real costs vary with traffic, speed, weather, load and driving style, and with charging losses for an electric car.
Can I change to a different tyre size safely?
Often yes, but keep the overall diameter within about 3% of the original unless the handbook allows more, and match the load index and speed rating. Check wheel offset and clearance too, and check with a tyre specialist.
Is wheel horsepower the same as engine horsepower?
No. Wheel power is lower because of drivetrain losses. The calculator lets you enter a loss percentage, and the result is an estimate rather than a measured dyno figure.
Do these tools include mileage claims for tax?
No. They are for driving costs and vehicle maths. Business mileage rates and tax rules are not covered.