Operator math, worked
How to calculate pounds of chlorine to disinfect a pipe
To disinfect a new pipe you dose it to a target strength. Finding the pounds needed puts three steps together: the pipe volume in gallons, then in million gallons, then the pounds formula. It looks long but each step is small.
Last reviewed 2026-08-04
The formula
pounds = pipe volume (MG) x dose (mg/L) x 8.34
The steps
Find the pipe volume in cubic feet
A pipe is a long circle: 0.785 x diameter x diameter x length, all in feet.
Turn it into gallons, then million gallons
Multiply cubic feet by 7.48 for gallons, then divide by 1,000,000 for MG.
Use the pounds formula
Multiply the volume in MG by the dose in mg/L by 8.34.
Worked example
Disinfect a 6-inch (0.5 ft) pipe, 1,000 feet long, to 50 mg/L. How many pounds of chlorine?
- Cubic feet: 0.785 x 0.5 x 0.5 x 1,000 = 196.25 cubic feet
- Gallons: 196.25 x 7.48 = 1,468 gallons
- Million gallons: 1,468 / 1,000,000 = 0.001468 MG
- Pounds: 0.001468 x 50 x 8.34 = 0.61 pounds
Answer: about 0.61 pounds of chlorine
Common questions
- How do I get the pipe diameter in feet?
- Divide inches by 12. A 6-inch pipe is 0.5 feet.
- Why convert to million gallons?
- The pounds formula uses flow or volume in millions of gallons (MG).
- What dose is used to disinfect a pipe?
- It depends on the procedure; the exam gives you the target mg/L to use.