There's one more online tool we find indispensable - especially when doubling, halving, or multiplying a recipe (wedding cake, say) to feed a crowd.
This resource is low-key and easy to use, but it will make your life so much easier when cooking for a crowd. It's called the Recipe Quantity Calculator, and it takes in the recipe you want to multiply and does all the challenging math work for you.
We like how flexible it is; you can use your own units or the pre-programmed ones. You can also multiply recipes by any factor you like, which means you can halve, or divide by eight, or multiply by 29. Whatever - this takes some of the head scratching out. Because, even if you're very competent at math, recipes can be a little overwhelming sometimes with all their quantities and units. We've found this a very helpful tool when working on big meals or projects.