Operator math, worked
How to calculate pounds per day of a chemical
To dose a chemical like chlorine, you often need pounds per day. The pounds formula ties the flow, the dose, and the weight of water together. It is one of the most-tested operator calculations.
Last reviewed 2026-08-04
The formula
pounds per day = flow (MGD) x dose (mg/L) x 8.34
The steps
Get flow in MGD
Make sure the flow is in million gallons per day. If it is in GPD, divide by 1,000,000.
Multiply the three parts
Multiply the flow (MGD) by the dose (mg/L) by 8.34, the pounds in a gallon of water.
Worked example
A plant treats 0.5 MGD and doses 8 mg/L of chlorine. How many pounds per day?
- 0.5 x 8 = 4
- 4 x 8.34 = 33.36 pounds per day
Answer: 33.36 pounds per day
Common questions
- Why 8.34?
- A gallon of water weighs 8.34 pounds, which links gallons to pounds of chemical.
- What if flow is in GPD?
- Divide GPD by 1,000,000 to get MGD first.
- Does this work for any chemical?
- Yes, for a chemical dosed in mg/L; adjust for purity if it is not 100 percent.