Conversions and calculators - 2026

Imperial versus metric measurements

Imperial Units of meaurement evolved from ancient Roman and Anglo-Saxon systems. England began standardising these local measurements over centuries, culminating in the Weights and Measures Act of 1824, which legally codified the British Imperial system. These units, like inches, feet, pounds, and gallons, were often based on natural references (a king's foot, a grain of wheat). The Dutch word for "inch" (duimi>), for example, can also translate to "thumb".

The USA used these measures while they were a British colony, but after their independence they retained many pre-1824 English units. Crucially, while the UK standardised the imperial gallon and bushel to be smaller, based on the volume of water, the USA retained the older, larger "Queen Anne" gallon and bushel. This is the primary reason for differences – US "imperial" (often just called "US Customary") units reflect an older stage of British standardisation.

During the French Revolution, the Metric System arose from a desire for a rational, universal system based on decimal units and fundamental constants (initially related to the Earth). Defined in 1799 with the metre and kilogramme, it offered advantages of simplicity and coherence. The metric system gradually gained international acceptance, especially in science and trade, ultimately becoming the dominant global standard.

Today, the UK officially uses the metric system for most purposes, although imperial units remain in common use for some applications, like road distances (miles) and beer (pints or quarts). The USA is a notable exception, still primarily using US customary units in daily life, alongside metric units in science and some industries. The evolution of standards during these colonial periods is why we have the imperial/metric divide and the nuances between UK and US imperial units.

Distance Conversions

• millimetres to inches, inches to millimetres
• metres to feet, feet to metres

Area Conversions

• square metres to square feet, square feet to square metres/li>
• Acres to hectares, hectares to acres
• square metres to acres, acres to square metres

Temperature Conversions

• celsius to Fahrenheit, Fahrenheit to ceclsius

Weight Conversions

• kilogrammes (kg) to pounds (lb), pounds (lb) to kilogrammes (kg)

Calculators

• Calculate the capacity of a petrol or diesel engine

  Calculate swept capacity from bore, stroke and number of cylinders. You can provide input in either metric (mm) or imperial (inches) measurements, and both metric (cc) and imperial units (cubic inch) are calculated and shown in the results.

  A history of your previous calculations is retained, and you can download that as a CSV file if you like.

• Weight distribution calculator

  Calculate and convert weight and weight distribution. Metric to imperial: kilogrammes to pounds, and vice versa. Your calculation history is tabulated and can be downloaded as a CSV file.

• Monthly vehicle loan repayments calculator

  Get an estimate on the monthly repayment for your car, in any currency. Change the deposit, trade-in and balloon (residual) payments, length of loan, and see how much you would have to pay monthly. It's a rough guide to figuring out what you could afford to pay for. Always get a full quote from your finance company, they will likely have monthly admin and setup fees over and above your basic repayments.

• Horsepower and torque conversions

  Convert between brake horsepower (bhp), ps/cv/metric horsepower and kiloWatts (kW). Torque figures can be converted to and from kilogramme-metres, Newton-metres and pounds foot or inch. You can also optionally calculate the brake mean effective pressure (bmep) an engine produces.

• Fuel consumption conversions

  Convert fuel economy figures to and from litres per 100 kilometres (l/100km), kilometres per litre (km/l), US and UK miles per gallon (MPG). You can optionally calculate the theoretical range and the carbon dioxide emissions (grams of CO₂per kilometre).