What is chlorine demand?

Chlorine demand is the amount of chlorine consumed by organic matter, bacteria, iron, manganese, and other substances in the water before a measurable residual remains. It must be satisfied before any free residual chlorine can persist. Typical values range from 0.2 mg/L for clean groundwater to 3–5 mg/L for surface water.

What residual concentration should I target?

The US EPA recommends a minimum free chlorine residual of 0.2 mg/L at the consumer tap. Treatment plants typically dose to maintain 0.5–1.0 mg/L at the point of entry to the distribution system. Swimming pools typically target 1–3 mg/L free chlorine.

How do I convert dose to a liquid bleach volume?

Household bleach is typically 5.25–8.25% sodium hypochlorite by weight (52,500–82,500 mg/L available chlorine). Divide the required chlorine mass in mg by the bleach concentration in mg/L to get the volume of bleach in liters. The calculator shows the pure chlorine mass — then apply your bleach product's concentration.

Does this account for chlorine loss over time?

No. This tool calculates the instantaneous dose needed to meet demand and residual at the time of treatment. For systems requiring sustained residuals over long retention times, add a safety factor or consult chlorine decay modeling software.

What units does the calculator support?

Water volume can be entered in liters, US gallons, or cubic meters. Concentrations are always in mg/L (milligrams per liter, equivalent to ppm by mass for dilute aqueous solutions). Results are shown in grams, kilograms, and pounds.

Chlorine Dose Calculator

Enter your water volume, chlorine demand, and target residual to get the exact chlorine dose needed for effective water treatment.

Dosing Parameters

Water Volume

Chlorine Demand (mg/L)

Amount of chlorine consumed before any residual remains.

Desired Residual (mg/L)

Target free chlorine residual after treatment (EPA minimum: 0.2 mg/L).

Results

Enter your parameters and click Calculate.

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Summary

Enter your water volume, chlorine demand, and target residual to get the exact chlorine dose needed for effective water treatment.

How it works

Enter the volume of water to be treated (liters, gallons, or cubic meters).
Input the chlorine demand of the water — the amount consumed by organic matter and other substances before a residual remains.
Set the desired chlorine residual concentration (mg/L) you want to maintain after treatment.
The calculator adds demand and residual to get the total dose, then multiplies by volume.
Results are shown as pure chlorine equivalent (100% Cl₂) in grams, kilograms, and pounds.

Use cases

Sizing chlorination systems for municipal water treatment plants.
Calculating disinfectant dosing for swimming pools and recreational water.
Calculating pure chlorine requirements before adjusting for commercial bleach or hypochlorite concentrations in field purification.
Designing chlorination for wells, storage tanks, and distribution mains.
Validating chlorine feed rates during water system commissioning.
Teaching environmental engineering students about disinfection dosing.

Frequently Asked Questions

Last updated: 2026-09-19 · Reviewed by Nham Vu