All cars in the world (including all those in the USA) have been fully metric since the development of interchangeable parts for the “world car concept” in the early 1970s.


Every modern family car has (about) 10 000 separate parts, each of which requires (say) 10 measurements. All cars have been measured some 100 000 times — using metric measures — often to the nearest 100 micrometres (1 micrometre is a millionth of a metre, it is also a thousandth of a millimetre, and is sometimes referred to as a micron, although micrometre is the preferred unit name).


Petrol and diesel fuel has been sold in litres for many years, making price comparisons very easy over time, and in comparison with other countries. In October 2004, when petrol cost around 80 pence per litre in the UK, it was costing only 30 pence per litre in the Middle-eastern country of Jordan.


Engine sizes have always been measured in cubic centimetres and litres. A typical engine size for a small car would be 1000 cc, which is also 1 litre, for a mid-size car around 1400 cc, which is 1.4 L, and for a larger car it might be 2000 cc, which is 2 litres. This capacity is not the actual size of the engine, but rather it refers to the the displacement or swept volume by the pistons of the engine (the total volume of air/fuel mixture an engine can draw in during one complete engine cycle, as the pistons are moved from top dead centre to bottom dead centre).