⇄Unit Converter

A US pint is 473ml. A UK pint is 568ml. That twenty percent gap is the single most common source of converted recipes going wrong, and neither cookbook mentions it.

The same split runs through fluid ounces and gallons. A US gallon is 3.79 litres, an imperial gallon is 4.55. If a conversion result feels wrong when crossing the Atlantic, volume is almost always why.

Cups do not convert to grams

Cups measure volume, grams measure weight, and the relationship depends entirely on what is in the cup. A cup of flour and a cup of sugar weigh substantially different amounts. There is no single conversion factor, and any chart offering one is quietly assuming an ingredient.

This is why baking recipes written in grams are more reliable than the same recipe in cups, and why serious baking books switched.

Temperature works differently

Length and weight conversions are multiplication. Temperature is not, because Celsius and Fahrenheit have different zero points, so converting needs an offset as well as a scale.

The consequence that catches people: a temperature interval does not convert the same way a temperature does. A rise of 10 degrees Celsius is a rise of 18 degrees Fahrenheit, not the 50 you get by converting 10C directly.

The exact factors

An inch is exactly 25.4 millimetres and a pound is exactly 0.45359237 kilograms. Both are fixed by international agreement rather than measured, which is why conversions between them are exact rather than approximate.

Screen sizes

Measured diagonally, so a 15 inch laptop is nowhere near 15 inches wide. Converting the diagonal tells you very little unless you also know the aspect ratio — which is why two laptops with the same stated size can have noticeably different keyboards.