Whole-grain wording differs by country and manufacturer. The ingredient list is the best place to confirm which grains are actually used and where they appear.
Look for specific grain names
Useful wording identifies the grain, such as whole-grain oats, whole wheat, whole-grain rye, whole-grain barley or whole-grain maize/corn. A broad phrase on the front does not reveal the proportion in the recipe.
Read the order
Ingredients are generally listed in descending order by weight under local rules. When a whole grain appears first, it is the largest single ingredient, but the full recipe can still include refined grains, sugars, oils and flavourings.
Do not confuse colour with grain content
Dark colour may come from cocoa, molasses, malt or colouring. Pale cereal can still use whole grains. Visual appearance is not a reliable test.
Compare similar formats
A whole-grain granola and a plain whole-grain flake can differ greatly in oils, sweeteners and density. Start with the format you want, then compare whole-grain options within it.