Identify your dish: pasta sauce, pizza base, braise, or stew—then match the substitute by thickness (pourable vs. reduced).
Use the listed ratio. For concentrated options (tomato paste), thin with water or broth until it coats a spoon.
Simmer if the substitute is watery (crushed or diced tomatoes) so it reduces into a tomato-sauce body.
Taste for sweetness and salt. If it’s too sweet, simmer a little longer; if it’s too sharp, add a pinch of sugar or a splash of fat.
Adjust seasoning after swapping (garlic, oregano, pepper) so the flavor reads like tomato sauce in your specific recipe.