When canning tomatoes, whether whole, halved or diced, each quart requires about 3 pounds of tomatoes. How many actual tomatoes required per quart varies largely on the type of tomato used, with larger varieties such as Early Girl requiring fewer tomatoes and smaller varieties like Roma requiring more.
When chopped fresh, the actual number of tomatoes per quart is highly variable based on variety; however, the per pound amount is the same. Three pounds of tomatoes yields about 4 cups of diced tomatoes when packed firmly into a measuring cup. Tomatoes, made largely of water, lose much of their mass when cooked.