TDIFFUNwomens Td-914 Shapewear Tank Tops (pack of 3)

It seems wrong that a 3xl seems is for a 30 in bust. what is that all about? a 3 x is about a 48 in bust in american sizes. what is the true sizing?

I weigh 140, 5'7, size m or l usually. what size should i get?