Identify your use case: roasting/chunky sauce (fresh-like texture) vs. smooth simmered sauce (consistent cooked flesh).
Choose a substitute from the best-match set first (Roma or canned whole plum tomatoes).
Use the listed ratio; if the substitute is wetter than plum tomatoes, drain/strain or simmer 5–10 minutes longer.
Adjust after cooking: add a pinch of salt for under-seasoned swaps, or simmer longer to reduce sweetness.
Taste at the end and confirm thickness—your sauce should coat a spoon without looking diluted.