I was explaining a recipe to my girlfriend over SMS. I wanted to tell her that for each cup of rice she added to the recipe, she should pour in an additional cup of water, too.
I texted:-
You should add twice as many cups of water as of rice.
That is, if she added, say, 4 cups of rice, she should pour 8 cups of water into the pot.
I know the sentence is comprehensible because she managed to fix the dish, but I am unsure if the sentence is correct or idiomatic.
Can someone tell me if this sentence is OK?