Describe by clothes size, not body size, e.g.
I bought a black and cream floral midi tea dress from Plumptious. The garment measures a comfortable 48” in the bust, with a generous 54” of gorgeous fabric across the hips. It fits as though it were made for me! According to Plumptious' size chart, this fits a UK size 18-22.
@Auntflo Plumptious is a beautiful portmanteau.
* We have a word in Scots, ‘sonsie’ which means ‘attractive and healthy in appearance’. It's similar to ‘Bonny’, which means ‘pretty’, not ‘fat’ 
* ‘Ah, what a bonny lass!’ = That bloke’s into her 
We don’t have a word for fat - probably because traditionally, we were too poor to get fat:
Oats: “A grain, which in England is generally given to horses, but in Scotland supports the people.” Samuel Johnson, Dictionary of the English Language (1755)