All fertilizer labels have three bold numbers. This label, known as the fertilizer grade, is a national standard.
Blends contain particles of more than one color.
Manufacturers produce different grades for the many types of plants. You can also get fertilizers that contain only one of each of the primary nutrients. Do the same for calculating the amounts of phosphate and potash. The remaining weight is filler, usually sand or granular limestone. Multiply 50 by .08, which equals 4.