My classic cheesecake recipe calls for 20 graham crackers finely crushed. How many cups of ready crumbs would this be?

Should be about 2 1/2c unless it means the square, half- crackers, which your numbers indicate. The recipe I use for a 9" pie is 10 whole crackers, 1/4c. butter, 2Tb. sugar, but I think 1/4c. sugar is more usual- I don't like things too sweet.