Assuming you are baking brownies from scratch, the general rule of thumb is to bake them for about 30 minutes. This will give you chewy, fudgy brownies. If you want cake-like brownies, you would bake them for closer to 40 minutes. Keep in mind that every oven is different, so it's always best to check your brownies a few minutes before the suggested time to see how they are coming along. You don't want to over or under bake them!