Identify what amaranth is doing in your recipe: grain base (chew), porridge/thickener, or baking structure (binder/flour).
Use the matching substitute from the table: choose the closest texture (cooked grain vs. ground flour) first.
Apply the ratio from the reference table; if your substitute is coarser or drier, add a small splash of liquid during cooking.
Adjust at the end: taste for bitterness/earthiness, then fine-tune thickness by adding 1–2 tablespoons more liquid or letting it simmer 1–2 minutes longer.
If substituting in baking, let the batter/rest time absorb moisture (about 5–10 minutes) before baking for better structure.