"Can I replace canned tomatoes with fresh in a recipe? If the recipe calls for one 14.5 ounce can, how many tomatoes should I use?"
You can usually substitute 2 cups of fresh chopped tomatoes for one 14.5-ounce can of diced tomatoes. If a recipe calls for whole canned tomatoes, you will need to peel yours, and if the recipe calls for canned tomato puree, you will need to cook and puree your fresh tomatoes—or stick with canned.
For more recipe ideas, see 7 Ways with Fresh Tomatoes.