Measure your chosen substitute at the adjusted ratio listed above (e.g., 1 teaspoon bouillon per cup).
If the substitute is solid (kombu/bonito or shiitake), steep or simmer as directed (see notes) and strain before adding to the recipe at the same stage you would add dashi.
Taste and adjust salt: when using instant bouillon, reduce added salt by about ¼ teaspoon per cup of broth; when using mushroom dashi, add 1 teaspoon soy sauce per cup for fishiness if needed.
For baking or dry-seasoning uses, dissolve powdered blends into the recipe liquid first to avoid gritty texture; use powder at 1 teaspoon per cup reconstitution equivalence.