Sour cream is a separate ingredient from yogurt and cream cheese. Choose its own reference even when another ingredient appears to have a similar consistency or a familiar cup weight.
Read what each source establishes
King Arthur groups low-fat and full-fat sour cream under a recipe convention. The entry does not supply separate physical-density measurements for those products.
Women’s Weekly Food provides a 250 mL cup relationship but does not specify fat percentage or brand. The physical volume is defined; the product detail remains limited.
Scale a package weight directly
Use a stated weight when the recipe or package provides one. A fraction of a known mass can be scaled without estimating how it fills a cup.
For “half a container,” record the actual container size before calculating. Keep any instruction to drain or otherwise prepare the ingredient in the note rather than silently assuming the reference covers that state.
Keep the ingredient distinct in output
A shopping list should preserve sour cream as its own identity, including a product preference supplied by the recipe. Similar dairy names should not be merged automatically.
Before printing a volume estimate, check that its source and state are still visible. The number alone does not communicate the product scope behind it.