Entering and displaying fractions or Broken Numbers recorded as decimal numbers

When a recipe, ingredients are ALWAYS written with the quantity as a fraction, 1/3 cup, 1 1/2 tsp, 1 3/4 cup, 1/3 tbsp, etc.

I want the user to be about to enter the ingredient quantity as a fraction (and displayed as such as well).

I am creating a recipe site that will do calculations using the quantity of ingredients added to the recipe. So we need the fraction entered to record/convert to a decimal number for the calculation.

Can any one please suggest any ways this can be done.