Feet, like any other part of our body, are measured in centimetres. If you’re asking about why shoe sizes are in numbers, there’s an interesting story to this. The standard way to do shoe sizes is to take three times the foot size in inches, and then take away 25, or 12 for kids’ sizes. The reason for this complicated system is because shoes used to be measured not in inches or centimetres, but in an Old English unit called the ‘barleycorn’ that amounts to one-third of an inch.