Take these two sentences:
1. You're supposed to drink up to your body weight in grams of water.
2. The average woman uses her height in lipstick every 5 years
I can understand that in the first, you're supposed to drink as much water(in grams) as your weight,
i.e. if your weight is 120lbs, drink 120 grams
And in the second if the person's height is 169cm, then they use that much lipstick every 5 years.
But I haven't found a definition for this kind of usage. So I was wondering is the word 'in' meant to show equality or correlation?
I'm pretty sure that it is, but would like some confirmation.