I've just dug out an old sewing pattern
Size 8 = bust 31 1/2, waist 24, hips 33 1/2
Size 10 = bust 32 1/2, waist 25, hips 34 1/2
Size 12 = 34, 26 1/2, 36.
Size 14 = 36, 28, 38.
Size 16 = 38, 30, 40.
I've just looked at Next sizing, who are generous and they are bigger by three inches for each size on the waist.
So I'm inbetween a 16-18, but really I'm 18-20. But we have changed body shape thanks to better nutrition and the Pill, as well as not wearing girdles, as said.
It isn't the leap that some would like to claim, though.