Chlorine Dosage & Residual Calculator
Calculate chlorine dosage, chlorine demand, or residual chlorine for water treatment and disinfection applications.
Optional: Flow-Based Mass Loading
Formulas Used
Chlorine Residual = Dosage − Demand
Chlorine Dosage = Demand + Residual
Chlorine Demand = Dosage − Residual
Mass Loading (lbs/day) = Concentration (mg/L) × Flow (MGD) × 8.34 lb·L/(mg·gal)
All concentration values are in mg/L (ppm).
Assumptions & References
- Chlorine demand is the amount of chlorine consumed by reactions with organic matter, ammonia, iron, manganese, and other reducing agents before a residual is established.
- The conversion factor 8.34 lb/gal is the density of water at standard conditions (AWWA standard practice).
- EPA Maximum Residual Disinfectant Level (MRDL) for chlorine: 4.0 mg/L (40 CFR Part 141.65).
- EPA minimum free chlorine residual in distribution systems: 0.2 mg/L (40 CFR Part 141.72(b)).
- Typical target residuals range from 0.5–1.0 mg/L at the point of entry and 0.2 mg/L minimum throughout the distribution system.
- This calculator assumes free chlorine (Cl₂, HOCl, OCl⁻). Combined chlorine (chloramines) calculations require separate breakpoint chlorination analysis.
- References: AWWA M20 Water Chlorination/Chloramination Practices and Principles; USEPA Disinfection Profiling and Benchmarking Guidance Manual (EPA 816-R-03-004).