Madhur Jaffrey informs me (Eastern Vegetarian Cookery, p103) that � lb (225g) of dried chick peas will yield about 1� lb (675g) of cooked, drained chick peas. My can of supermarket own label cooked chick peas weighs 400g net, which gives 240g in drained weight. Therefore, every 400g can of chick peas your recipe suggests, you need 80g of dried peas. Don't forget to soak the peas for at least 12 hours and then they will need cooking for about an hour (longer if they are old).