The mathematics of a third-degree burn in multiples of nine

Crime reporters often write about victims of fire and the extent of burns on their bodies. Here's a typical example: 'A woman who suffered burns to 63 per cent of her body when a pot of boiling congee tipped over her was yesterday awarded HK$1.9 million compensation. She suffered second-degree scalding to 40 per cent of her body, and deep burns to 63 per cent.'

But how do medics calculate burn percentages? Apparently, they rely on a rule of thumb by using the 'rule of nine'.

You can estimate the body surface area on an adult burn victim by using multiples of nine. The percentages involved can be roughly calculated as follows:

Head = 9 per cent

Chest and abdomen = 18 per cent

Upper/mid/low back and