Tomatoes

From Cooks Illustrated (may need an account to view this article):

• 1 lb fresh tomatoes = 1 14.5-oz can of drained diced tomatoes + 1 T of drained juice
• 28-oz can of diced tomatoes = 2-1/2 cups of drained tomato solids
• 28-oz can of whole tomatoes = 1-3/4 cups of drained tomato solids

Calcium chloride often added to canned diced tomatoes helps tomatoes retain structure, so better to use whole tomatoes when making sauce.

San Marzano tomatoes

• A type of plum tomato grown near Naples, Italy -- supposedly in the shadow of Mt. Vesuvius
• Canned Marzanos grown in Italy in compliance with Italian law will have the EU "DOP" emblem on the label.
• Read the label carefully and look for the EU "DOP" (Denominazione d'Origine Protetta) emblem; even tomatoes labeled as "San Marzanos" may not be the real deal.
• Brands of canned San Marzano tomatoes include LaValle, Francesconi, La Bella, Coluccio, Sclafani, Cento, Cirio, and Vanita.
• Apparently, Food & Wine magazine named LaValle San Marzanos the best in a taste test.

References

• http://en.wikipedia.org/wiki/San_Marzano_tomato
• http://www.thecitycook.com/cooking/articles/fab/000021