Use this chlorine dosage calculator to size free chlorine dosing, set the metering pump, and estimate CT (contact time) and contact tank volume. It supports sodium and calcium hypochlorite stocks and simple volume dilutions.

• Rapid sizing of free chlorine dose and metering pump setpoint.
• Built-in methods for sodium and calcium hypochlorite stocks.
• CT (contact time) estimate to screen contact tank volume.

How to read results from the chlorine dosage calculator

The calculator reports the required dose (mg/L), the pump setpoint in L/h and L/min, the estimated daily chemical usage, and—if CT inputs are provided—the contact tank volume based on your selected baffling factor. Use these values as engineering estimates and validate them on site.

Quick start — How to use the Chlorine Dosage Calculator (step-by-step)

1. Enter the flow rate and choose m³/h or gpm.
2. Set your target free chlorine and current residual. If you expect consumption from ammonia/organics, enter a chlorine demand (start with 0.5–2.0 mg/L if unknown, then tune with online residual or ORP).
3. Define the stock solution:
   • Liquid NaOCl: % available chlorine and density (kg/L)
   • Solid hypochlorite: grams per liter and % available chlorine
   • Volume dilution: known stock mg/L and a 1:R dilution
4. (Optional) If you need CT, enter the target CT, terminal residual \(C_\mathrm{out}\), and choose a baffling factor that reflects your contactor hydraulics.
5. Click Calculate. The tool returns the required dose, metering pump setpoint (L/h, L/min), daily chemical usage, and (if CT is enabled) the recommended contact tank volume.

Inputs & units

• Flow rate — process water flow; switchable between m³/h and gpm.
• Target free chlorine — desired residual after contact (mg/L).
• Current free chlorine — measured residual before dosing (mg/L).
• Chlorine demand — site-specific consumption from ammonia/organics. If unknown, start at 0 and increase based on residual or jar tests.
• Stock definition — choose NaOCl (% + density), solid (g/L × %), or volume dilution (mg/L and 1:R).
• CT & baffling factor — CT in mg·min/L; baffling factor \(T_{10}/\tau\) accounts for short-circuiting (see table below).

Equations & methodology

Required dose (mg/L):
  Dreq = max(0, Ctarget − Ccurrent + Cdemand)

Stock strength (mg/L as Cl₂):
  Liquid NaOCl: Cstock = (%AvailCl/100) × 1,000,000 × ρ   (ρ in kg/L)
  Solid solution: Cstock = s(g/L) × (%AvailCl/100) × 1000
  Volume dilution: Cstock = C₀ / (1 + R)

Pump setpoint (L/h):
  Pump = Dreq × 1000 × Q(m³/h) / Cstock

Estimated daily usage (L/day):
  Daily = Pump × 24

Contact tank volume (m³):
  V = (CT × Q(L/min)) / (Cout × BF) / 1000

Notes: For dilute aqueous solutions, 1 mg/L ≈ 1 ppm. Choose a conservative baffling factor unless tracer testing is available.

Worked examples

Example A — Sodium hypochlorite dosing only

• Flow = 20 m³/h; Target = 0.8 mg/L; Current = 0.1 mg/L; Demand = 1.0 mg/L ⇒ Dreq = 1.7 mg/L
• NaOCl 10% with density ρ = 1.16 kg/L ⇒ Cstock ≈ 116,000 mg/L
• Pump setpoint = 1.7 × 1000 × 20 / 116000 ≈ 0.293 L/h (~0.0049 L/min)
• Daily usage ≈ 7.0 L/day

Example B — With CT & contact tank

• Using Example A values + CT = 30 mg·min/L; Cout = 0.5 mg/L; BF = 0.35
• Q = 20 m³/h = 333.3 L/min ⇒ V = 30 × 333.3 / (0.5 × 0.35) / 1000 ≈ 57 m³

Example C — Solid hypochlorite stock

• Make-up: 50 g/L of 65% available chlorine ⇒ Cstock = 50 × 0.65 × 1000 = 32,500 mg/L
• For Dreq = 1.5 mg/L and Q = 12 m³/h ⇒ Pump = 1.5 × 1000 × 12 / 32500 ≈ 0.554 L/h

Reference tables

Sodium hypochlorite — typical density & strength

Always prefer the supplier’s SDS/COA values.

Baffling factor (T₁₀/τ) selection

Day tank sizing (rule of thumb)

Recommended day tank volume ≥ daily usage × N days × 1.2 (20% safety margin). For critical utilities, provide level monitoring and secondary containment.

Best practices & safety

• Verification: Control with online free chlorine or ORP, and confirm residual at the end of contact.
• Shelf life: Hypochlorite decays with time, heat, light, and metals contamination. Re-check stock strength periodically and adjust the pump setpoint.
• Materials: Use compatible plastics (PE, PVC, PP) or lined steel. Avoid copper/brass/plain carbon steel in wetted parts.
• Containment & ventilation: Provide secondary containment, vented tanks, and local exhaust where appropriate.
• Operator safety: Follow PPE requirements and local regulations for chemical storage and handling.

FAQs

Is mg/L the same as ppm in this chlorine dosage calculator?

For dilute aqueous solutions, mg/L ≈ ppm. The calculator uses mg/L to match drinking-water practice.

What if I don’t know the chlorine demand?

Start with 0 mg/L and adjust based on online residual, ORP, and jar tests. Raw waters with ammonia/organics often require additional dose to satisfy demand.

Why do I need the density for sodium hypochlorite?

Percent available chlorine is by weight; density converts to mg/L as Cl₂. If SDS/COA is unavailable, use the typical values in the table as a starting point.

Does this tool handle chloramination?

No. This calculator assumes free chlorine. Chloramine systems require ammonia feed and breakpoint chemistry; design them separately.

How accurate is the contact tank estimate?

It’s a planning estimate based on your selected baffling factor. For regulatory CT credit, verify hydraulics with tracer studies and follow local rules.

Related tools & products

• Chemical Dilution Calculator
• GAC & Media Filter Sizing (EBCT)
• RO Sizing Calculator
• RO OPEX Calculator
• Chemical Dosing Systems & Contact Tanks — engineered packages from STARK Water

Engineering disclaimer: Results are estimates and must be field-validated. Always follow local drinking-water regulations and safety codes.

Authoritative references

• US EPA – Drinking Water Disinfection & CT concepts
• WHO – Guidelines for Drinking-water Quality