How much crushed eggshell should I add to kitten's raw diet consisting of 1/4 cup of meats per meal?

I am transitioning my kittens to an all raw diet. They seem to be doing really well on it, but I have some concerns with making sure it is nutritionally balanced. Having researched the calcium to phosphorous ratio, I have decided to use crushed eggshells as the calcium source. Can someone please tell me if I feed about a ¼ cup of meat what amount of crushed eggshells should I add to make a 1.5:1 calcium to phosphorous ratio?

Note: I currently do not have a grinder so I crushed the eggshells as much as I could by smashing them with a piece of wood. The pieces are not exactly a fine powder.