Choose the substitute that matches your goal: closest flavor (ancho/New Mexico), deeper richness (mulato/pasilla), or smoky shortcut (chipotle).
Rehydrate dried chiles (cover with hot water 15–20 minutes) if your recipe uses blended guajillo paste; then seed and blend smooth with the same cooking liquid.
Use the ratio from the table to start (most are 1:1; chipotle start at ¾).
Adjust after blending: add a pinch more heat (extra chile powder) if flat, or add acidity (lime/vinegar) if it tastes too round or sweet.
Taste in-context: simmer the blended chile 2–5 minutes in the sauce so the flavors meld before final seasoning.