I keep neither, but I do have tomato powder (from a restaurant supply store - and it does not clump) and canned tomatoes (6-in-1 brand). I use tomato powder plus a small amount of water in place of tomato paste, but I generally only add it to a sauce that is too watery, or when I want to add tomato flavor but not liquid.

To make tomato sauce, I simply puree the canned tomatoes. If you have good canned tomatoes (make sure they do not have citric acid added), you have tomato sauce. A stick blender will do a quick job of making the sauce. In Italy, the only ingredient I noticed in tomato sauce was tomatoes and perhaps olive oil, especially on pizzas.

Sun dried tomatoes are good to have for other reasons, but I've not used them in sauce.

Paste is many times more concentrated than sauce, best used for deep, rich tomato flavor without the addition of a lot of liquid. Paste could be diluted and sauce could be reduced but Sun dried tomato will not replace either.

Sauce is cooked, more processed, with more ingredients. Also look for tomato puree, that's what I use for spag. sauce.

Actually, the crushed/puree does not have salt added. at least the cans that I have. All tomato, any sodium is naturally occurring.

Tomato paste has a richer flavor, perfect for putting it in soups for a tomato flavor. I use it in taco soup.

i make my own pasta sauce using crushed tomatoes.

Put all three on the counter and open them. Taste them. Very different and many varieties of each. A good grocery will have many varieties of canned tomatoes...diced, whole, pureed. Some better quality than others. Just a few small cans of paste usually, more concentrated and thick having most of the the moisture/water removed. Dried are usually sliced in thin strips for intense flavor in salads. (the most dried of the three and more moisture removed)...the flavor of dried whole /half tomatoes stay contained in the slices and usually does not permeate the dish with tomato liquid, so often good in a pasta salad. Or a garnish.

Not interchangeable as all play a different duty in different dishes. Often a personal choice. As i do not use paste tomato ever. Just don't like a thick tomato flavor...i use tomato powder if i want a punch after tasting a dish. Powder is just more convent.

thanks all for your comments. I will have to look up tomato powder. Had never heard of it.

The only thing about tomato powder is that it gets damp and turns into a hard chunk that's nigh on irretrievable if it's at all humid or exposed briefly to steam. Best to vacuum seal all but a small quantity, and put your small container in a larger container with some desiccant packets, or at least a piece of broken flowerpot. Otherwise, it's wonderful stuff, but I still like the cans better. I have made all my own, but unless you're growing them, it's really not worth it if you have good quality canned available.

I think of tomato paste as a base for building deep flavors and as a thickener.

I like taking a can of tomato paste and freezing it in tbsp dollops. Then I just take a glob and add to whatever I'm making. Often when making stews etc after sauteeing the vegetables and garlic I'll add a dollop of tomato paste and incorporate it. Then add broth, wine, etc.

I take leftover paste from the can and roll it in plastic wrap like a log and freeze. It slices easily into "coins".