Good question. NPK ratings are usually listed on the container the product comes in. I have the same question when making JBP fertilizer balls with cottonseed meal, blood and bone meal, garden lime and fish emulsion in different proportions. Their containers list specific amounts of NPK. Is their rating just the addition of the amounts of each the separate items and does that matter! Also: Why is a fall root fertilizer with cottonseed and bone meal listed as 0-10-10 when both items used separately contain nitrogen and some amount of potassium and phosphorus?