Automotive Calculators
Fuel economy and trip cost, tyre-size decoding, EV charging cost, gear ratios and engine displacement — your prices, your rates.
About these automotive calculators
The automotive tools share one discipline: anything that changes with the market is an input, never a built-in. Fuel prices, electricity tariffs and consumption figures are yours to type in, taken from your last receipt or your own dashboard, because a price baked into a web page would be wrong for most readers on the day it was published and wronger every day after. What the pages contribute is the arithmetic and the unit handling around those figures — the conversions between miles per gallon and litres per 100 km that catch out mental maths (the two scales run in opposite directions: higher MPG is better, lower L/100 km is better), and the geometry that turns a tyre sidewall code into the diameter and circumference figures everything else depends on.
That geometry is the quiet centre of the category. A code like 225/65R17 encodes section width, sidewall aspect and rim diameter, and from those three numbers come overall diameter, circumference and revolutions per mile — which is what the speedometer actually measures. The Tyre Size Calculator decodes two sizes side by side and shows the diameter difference and the true speed at each indicated speed, because fitting a tyre that is 3% taller makes every reading on the dial 3% optimistic. The Gear Ratio Calculator hangs off the same diameter: engine speed at a given road speed is the road speed multiplied by the total gearing and the tyre's revolutions per mile, and the Displacement Calculator is pure swept-volume geometry — bore, stroke and cylinder count — with the cubic-inch figure American specifications still quote.
The money tools stay deliberately simple. The MPG Calculator reports economy in both unit systems from one fill-up, the Fuel Cost Calculator multiplies a trip's fuel by your price and can split the result per passenger, and the EV Charging Cost Calculator prices a stated slice of a battery at your electricity rate with an idealised charge-time table by charger power — idealised, and labelled so, because real charging tapers as the battery fills. Every formula is printed on its page with worked examples, and every figure is computed in your browser: distances, prices and vehicle details are never uploaded, stored or tracked.
Frequently asked questions
Why do I have to enter fuel and electricity prices myself?
Because they are different on every forecourt and every tariff, and they change constantly. A built-in price would be stale data producing confident wrong answers. Your last receipt or your energy bill has the only price that applies to you, so the calculators ask for it and show it inside the working.
Which is better, a higher MPG or a lower L/100 km?
Both scales describe the same economy in opposite directions. Miles per gallon measures distance per unit of fuel, so higher is better; litres per 100 km measures fuel per fixed distance, so lower is better. They convert exactly: L/100 km = 235.215 ÷ MPG (US), and the MPG Calculator shows both from a single entry.
Do these tools store my trips or vehicle details?
No. Every automotive calculator runs entirely in your browser. Distances, fuel prices, tyre sizes and battery figures are calculated on your own device and are never sent to a server, stored or tracked.