Converting yarn requirements/crochet pattern

Hi,
after a long, long break, I’ve started crafting again. I really enjoy crocheting rectangular stoles; I’m not so fond of triangular shawls. I’ve already bought a few patterns for triangular shawls because I think the designs are so beautiful. But I’d rather crochet rectangular stoles.
My question is: How can I convert the yarn requirements for a triangular shawl to a rectangular stole?

That depends very much on how long and wide you want your stole to be. In my experience, you need at least a third more for a rectangle, but I’d plan on using even more.
If you have a triangular shawl with, say, a span of 150 cm and a depth of 50 cm, and you want the same dimensions but in a rectangular shape, then you’ll need twice as much yarn.

Thanks!