Chemical Dosing Calculator - Feed Rate, Pump Settings & Cost for Water Treatment
Calculate GPD or lbs/day feed rate for chlorine, alum, ferric, polymer, lime, caustic & more
Free chemical dosing calculator for water and wastewater treatment operators. Enter flow rate and target dose to get feed rate in gallons per day or pounds per day, metering pump settings, monthly chemical cost, and tank refill frequency. Supports sodium hypochlorite, calcium hypochlorite, chlorine gas, aluminum sulfate, ferric chloride, polymer, lime, sodium hydroxide, potassium permanganate, and fluoride compounds. Uses the standard lbs/day = Flow (MGD) × Dose (mg/L) × 8.34 formula with automatic specific gravity and concentration corrections.
Check chlorine contact time compliance
CT Value Calculator →Verify detention time for contact chambers
Detention Time Calculator →Calculate pump energy costs
Pump Energy Cost Calculator →How It Works
-
Enter Your Flow Rate
Input your plant flow in MGD, GPM, or GPD. The calculator converts everything to MGD internally for the dosing formula.
-
Select Your Chemical
Pick from the chemical database. Concentration and specific gravity auto-fill but can be overridden if your product differs from the default.
-
Set Your Target Dose
Enter the dose in mg/L (same as ppm). Typical ranges: chlorine 1-5 mg/L for disinfection, alum 20-150 mg/L for coagulation, polymer 0.5-5 mg/L for flocculation.
-
Read Your Results
Get feed rate in GPD for liquids or lbs/day for dry chemicals, plus metering pump setting, monthly cost estimate, and container refill schedule.
Built For
- Water plant operators setting chlorine feed rates after flow changes
- Wastewater operators adjusting coagulant dose for seasonal turbidity
- Operators verifying metering pump GPD settings match target dosing
- Plant managers estimating monthly chemical budgets for procurement
- New operators learning the relationship between mg/L, lbs/day, and GPD
Assumptions
- Feed rate formula uses the standard lbs/day = Flow (MGD) x Dose (mg/L) x 8.34 as specified in water treatment operator certification programs
- Chemical concentrations and specific gravities use manufacturer-typical values that can be overridden by the user
- Liquid chemical density is assumed uniform throughout the storage container (no stratification or settling)
- Metering pump output is based on the pump's rated capacity and assumes linear flow proportional to stroke or speed setting
- Monthly cost estimates assume constant flow rate and consistent chemical pricing over the billing period
- Sodium hypochlorite trade strength is as-delivered and does not account for degradation during storage
Limitations
- Does not account for chlorine demand from organics, ammonia, iron, or manganese — applied dose must exceed demand to achieve a residual
- Sodium hypochlorite degrades at 0.5-1.0% per month at room temperature and faster in heat — actual concentration may be lower than the label
- Does not model chemical interactions (e.g., chlorine and ammonia forming chloramines, or polymer interference with UV disinfection)
- Metering pump accuracy depends on calibration, back pressure, and suction conditions — field verification is required
- Does not calculate chemical storage inventory, secondary containment requirements, or shelf life management
- Fluoride dosing calculations are simplified and do not account for naturally occurring fluoride in the source water
- Not applicable to chlorine dioxide or ozone generation systems which have different stoichiometric relationships
References
- AWWA Manual M20 — Water Chlorination/Chloramination Practices and Principles
- EPA Guidance Manual for Compliance with the Surface Water Treatment Rules (LT1ESWTR)
- AWWA Standard B300-18 — Hypochlorites (sodium hypochlorite quality and handling specifications)
- Sacramento State University — Water Treatment Plant Operation, Vol. 1 (chemical dosing chapter)
- Ten States Standards (Recommended Standards for Water Works) — Chemical Application requirements
- AWWA Manual M12 — Simplified Procedures for Water Examination (jar testing and dosing verification)
Frequently Asked Questions
Learn More
How Chemical Feed Math Actually Works
Why mg/L is not the same as pounds per million gallons, how concentration and specific gravity change your feed rate, and why your sodium hypochlorite is weaker than you think.
CT Values: The Math That Keeps Water Safe
Why contact time is never as long as you think, how temperature kills CT credit in winter, and what T10 actually means for your disinfection compliance.
Related Tools
Detention Time Calculator
Calculate hydraulic detention time for any basin, tank, or lagoon and check against regulatory minimums. Supports rectangular and circular tanks with dead zone correction for actual vs theoretical retention time.
Disinfection CT Value Calculator
Calculate CT values for chlorine disinfection and verify EPA Surface Water Treatment Rule compliance. Check Giardia and virus log inactivation credits based on residual, contact time, temperature, and pH.
Water Tower Storage Sizing Calculator
Size elevated water storage based on fire protection, peak demand, and emergency reserve requirements. Follows AWWA guidelines for small water systems and rural water districts with standard tank size recommendations.