Crushed tomatoes – sub with diced or whole

If you are really set on doing this, just use the same amount by weight or volume, preferably peeling the tomatoes first. (Cut an x in the bottom, dip in boiling water for 10 seconds, pull off the peel). You'll have plenty of liquid coming out of the tomato, don't worry about that. But honestly, I don't recommend doing this. Fresh tomatoes that are any good are so good uncooked that it is a waste, and fresh tomatoes that aren't good won't get better by cooking them. Even Mario Batali says you should use canned tomatoes for cooked sauces.

Canned tomatoes, compared to fresh, are:

• Cooked. As part of the canning process, they are fully cooked.
• Peeled. Most canned tomatoes are peeled
• Acidic. For safety reasons, canned tomatoes often have additional citric acid added to the can (this prevents botulism growth)
• Ripe. The tomatoes to be canned are often vine ripened to a more ideal ripeness than retail tomatoes, and then immediately harvested, processed and canned.

Most of these attributes are actually an advantage in creating a pizza sauce, and so starting with a quality canned tomato may be far more convenient and flavorful than starting with raw tomatoes.