What is the formula for parts per million weight (PPMW)?

The formula for parts per million weight (PPMW) involves understanding the relationship between the amount of a chemical applied and the total volume of water in which it is distributed.

The correct formula, which states that you multiply the number of pounds of the chemical by 1,000,000 and then divide that by the product of the flow rate in cubic feet per second (CFS) and the time in minutes for which the chemical is applied, accurately captures this relationship. Essentially, this formula allows you to convert the amount of a substance into a concentration measurement that is meaningful in terms of very small quantities relative to larger volumes, which is what parts per million signifies.

In this context, when you divide the quantity of the chemical (in pounds) scaled up by a million, it provides a way to express that weight in relation to a much larger volume of water represented by the flow rate and the duration of application. The inclusion of both the CFS and the time in minutes ensures that you're accounting for the entire volume of water that the chemical interacts with, which is essential for accurate PPMW calculations in aquatic environments.

Understanding this formula is critical for pesticide applicators as it helps ensure that they are applying the right amount of chemical to effectively manage