what would be the equivalent amount of canned tomatoes in the Marcella Hazan sauce recipie

I'm assuming you're referring to today's Genius Recipe column? I agree with the professor -- definitely go by weight equivalent, accounting for the fact that some of the weight of a can of tomatoes is juice (i.e., you'll want to buy a larger can and weigh the tomatoes alone). I believe Kristen says in her post that this recipe works perfectly with a 28-ounce can of San Marzano tomatoes.

I would think you could go by weight (a 15 oz can of tomatoes = about a pound of fresh tomatoes).

What sauce recipe? She has many.