Where can I find a recipe calculator by ingredient?!

I'm looking for an online calculator that will help me modify a recipe by ingredient. I can only find ones that double or half the recipe or reduce/increase it by serving size. What I would like is one where you can enter the original recipe and then change the specific measurement of one ingredient and it will convert the rest for you. For example, if it calls for 4 1/2 cups of flour but I only have 2 3/4 cups... something that does the rest of the math for me. Anyone know if this kind of calculator exists???