Malaysia converted to the metric system in the 1970s, and officially everything is metres, kilograms and litres. In daily life the old units never quite left.

Property is still advertised in square feet, a person's height is often given in feet and inches while their weight is in kilograms, construction timber comes in feet, and imported recipes use cups and ounces. Switching between the two systems is a routine Malaysian task rather than an occasional one.

This is where conversions quietly go wrong. A US gallon is 3.785 litres and an imperial gallon is 4.546 litres — a difference of about 20%, which is more than enough to ruin a recipe or misjudge fuel economy.

This converter uses the US definitions, which are the ones you will meet in most online recipes and American product listings: cup 240ml, pint 473ml, gallon 3.785 litres. If you are working from an older British cookbook, its pint is 568ml and its measurements will not match.

Every other conversion here is a multiplication: a metre is always 3.28 feet, so double the metres and you double the feet. Temperature scales have an offset as well as a ratio, because zero degrees Celsius and zero Fahrenheit describe different things.

That is why 20°C is not half of 40°C in any meaningful sense, and why converting a temperature difference is not the same as converting a temperature. Kelvin is the exception — it starts at absolute zero, which is what makes it the scale scientists use when ratios need to mean something.

A handful of conversions cover most everyday needs. An inch is exactly 2.54cm. A kilogram is about 2.2 pounds. A mile is roughly 1.6 kilometres, so a 5km run is a bit over three miles. A foot is 30.48cm, near enough to a third of a metre for mental estimates.

For the kitchen, the one to remember is that a moderate oven at 180°C is 350°F. Most recipe temperatures cluster within 20 degrees of that pair, so you can usually estimate from it without reaching for a converter at all.