Skip to main content
Calcimator

Chlorine Dosing Calculator

Calculate chlorine dose and feed rate for water disinfection, including CT compliance for pathogen inactivation.

Inputs

MGD
mg/L
mg/L
minutes
°F

Results

Total Chlorine Dose

2 mg/L

Chlorine Feed Rate

41.7 lbs/day

CT ComplianceNon-Compliant — Increase dose or contact time
CT Achieved15 mg·min/L
CT Required75 mg·min/L
Log Inactivation0.4-log
NaOCl (12.5%) Feed33.4 gal/day
Cal-Hypo (65%) Feed64.2 lbs/day
Annual NaOCl Cost$42,617.00
Annual Gas Cl₂ Cost$6,088.00
DBP Formation RiskLow
How to Use This Calculator
  1. Enter Plant Flow Rate (MGD) and the Target Chlorine Residual (mg/L) required at the distribution system entry point.
  2. Input Chlorine Demand (mg/L) — this is typically determined by bench testing or historical operational data.
  3. Set Contact Time (minutes) for your clearwell or contact basin and select the Target Pathogen for CT table lookup.
  4. Enter Water Temperature (°C) — CT requirements increase significantly in colder water.
  5. Review Total Chlorine Dose and Chlorine Feed Rate (lbs/day) to set chemical feed pump outputs.
  6. Check CT Compliance status to verify your disinfection practice meets SWTR regulatory requirements.

How the result changes with Chlorine Demand

Chlorine DemandTotal Chlorine DoseChlorine Feed Rate
11.5 mg/L31.3 lbs/day
3.54 mg/L83.4 lbs/day
6.57 mg/L146 lbs/day
99.5 mg/L198.1 lbs/day

What each input means

Plant Flow Rate
Water flow rate in million gallons per day.
Target Chlorine Residual
Desired free chlorine residual after disinfection. EPA minimum: 0.2 mg/L entering distribution.
Chlorine Demand
Chlorine consumed by organics, ammonia, and metals before free residual is achieved.
Contact Time
Time water is in contact with chlorine before first customer (T10).
Target Pathogen
1 = Bacteria, 2 = Virus, 3 = Giardia, 4 = Cryptosporidium.
Water Temperature
Water temperature — colder water requires higher CT values.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Plant Flow Rate = 2.5, Target Chlorine Residual = 0.5, Chlorine Demand = 1.5, Contact Time = 30 = 6 input(s) provided
  2. Calculate Total Chlorine Dose
    Total Chlorine Dose
    2 = 2
  3. Calculate Chlorine Feed Rate
    Chlorine Feed Rate
    41.7 = 41.7
  4. Calculate CT Compliance
    CT Compliance
    Non-Compliant — Increase dose or contact time = Non-Compliant — Increase dose or contact time
  5. Calculate CT Achieved
    CT Achieved
    15 = 15

Related Calculators

The questions that sit next to this one — chosen by subject, including calculators filed under a different category.

Water Treatment

UV Disinfection Calculator

Calculate UV dose and reactor sizing for pathogen inactivation based on flow rate, UVT, and target log reduction.

Water Treatment

Water Treatment Plant Sizing Calculator

Size a water treatment plant from population, per-capita demand, and peak factors. Estimate basin, filter, and clearwell dimensions.

Water Treatment

Fluoride Addition Calculator

Calculate chemical feed rate for water fluoridation to achieve target concentration using NaF, fluorosilicic acid, or sodium fluorosilicate.

Pool & Spa

Hot Tub Chemical Calculator

Chemical doses for hot tub from volume and test results.

More in Environment, Weather & Climate.