The chemical dosage calculator converts a dose in mg/L (ppm) into a feed rate in kg/d, lb/day, L/h and mL/min and a dosing pump setting: kg/d equals mg/L x m³/d / 1,000, and lb/day equals mg/L x MGD x 8.34 / purity (Florida DEP formula table, 2014). Which strength, density and dose basis turn that mass into liters of product and a pump percentage?
Every dosed product among the water treatment chemicals uses the same arithmetic, so the calculator asks for the basis first.
The table lists the key figures.
| Constant | Value |
|---|---|
| Water weight | 8.34 lb per US gallon |
| Time | 1,440 min per day |
| Concentration | 1 % = 10,000 mg/L |
| Flow | 1 MGD = 3,785 m³/d |
| Volume and mass | 1 gal = 3.785 L; 1 lb = 454 g; 1 kg = 2.2 lb |
How Does the Chemical Dosage Calculator Work?#
The chemical dosage calculator works in 3 steps, from dose to daily mass, mass to product volume and volume to pump setting, listed below.
- Mass: dose x flow.
- Volume: mass / (strength x density).
- Setting: volume / pump maximum.
What Inputs Does the Dosage Calculator Need?#
The dosage calculator needs 5 inputs: the treated flow, the target dose with its basis, the product strength, the product density, and, for a pump setting, the pump's maximum output. Recommended Standards for Water Works (2022 edition, 5.4) asks plans for minimum, average and maximum doses, so the calculator returns all three.
The calculator accepts the following inputs and units.
| Input | Units offered | Default on load (worked example 1) | Rule shown to the user |
|---|---|---|---|
| Treated flow | m³/h, m³/d, L/s, gpm, MGD | 2,500 m³/d | above 0; 1 MGD = 3,785 m³/d, 1 gpm = 0.2271 m³/h, 1 L/s = 86.4 m³/d |
| Target dose (average; optional minimum and maximum) | mg/L (ppm) | 8.5 mg/L | above 0; minimum and maximum add result rows |
| Dose basis | as product, as active, as NaOCl, as Cl2, as dry alum, as Al2O3, as Al, as Fe, as F, as PO4, as P, as NaOH, as CaCO3 | as NaOCl | required |
| Product strength | wt %, g/L, trade % (hypochlorite only), lb/gal | 12.0 wt % | 0 to 100 %; trade % = g/L / 10; value from the certificate of analysis (CoA) |
| Product density or specific gravity | kg/L, g/mL, SG, lb/gal | 1.19 kg/L | required with wt %; unused with g/L |
| Basis fraction (product to basis) | %, decimal; presets: Al2O3 from the CoA, available chlorine 0.952 x wt %, available fluoride ion 0.452 / 0.607 / 0.792 | n/a | from the CoA; presets sourced |
| Pump maximum output | L/h, mL/min, gal/d, gph | 10 L/h | above 0 |
| Mode | continuous flow-paced, blowdown-paced, slug by system volume, calibration check (reverse), dilution and make-up | continuous | sets the input set |
| Blowdown flow / system volume | m³/h, gpm / m³, L, gal | blank | cooling and closed-loop modes only |
| Calibration data | g collected and minutes (dry); mL drawdown and minutes (liquid) | blank | reverse mode only |
| Tank volume | L, m³, gal | blank | optional; returns days of supply |
| Product MUL | mg/L as product | blank | optional, from the NSF listing |
What Does the Calculator Return: kg/d, lb/day, L/h and Pump Setting?#
The calculator returns kg/d and lb/day of chemical, L/d, L/h, gal/d and mL/min of product, a pump setting in percent and the days one tank lasts.
The calculator returns the following results.
| Result | Units | Shown with |
|---|---|---|
| Chemical mass per day | kg/d and lb/day | the basis entered ("as NaOCl") |
| Product mass per day | kg/d and lb/day of product | "as product" |
| Product volume | L/d, L/h, gal/d, gph, mL/min | strength and density used |
| Pump setting | % of maximum output; suggested stroke rate and stroke length | warning below 20 % (10 % with two adjustments) |
| Dose as product | mg/L as product | MUL comparison when entered |
| Days of supply | days and hours | day tank 30 h and storage 30 days notes |
| Minimum, average, maximum rows | all of the above | when minimum and maximum doses are entered |
| Actual dose (reverse mode) | mg/L on the chosen basis | the calibration inputs |
Which Formulas Convert mg/L into a Chemical Feed Rate?#
Four formulas convert mg/L into a chemical feed rate: two for daily mass (metric and US) and two for product volume or pump rate. Operators remember the pounds formula as the "Davidson pie": lb/day on top, MGD x mg/L x 8.34 below, divided by purity.
The calculator uses the following operator formulas; strength is a decimal (12 % = 0.12).
| # | Result | Formula | Source |
|---|---|---|---|
| 1 | Mass, metric | kg/d = mg/L x m³/d / 1,000 (= mg/L x ML/d) | EOCP Math for Operators |
| 2 | Mass, US | lb/day = mg/L x MGD x 8.34 / purity | Florida DEP formula table, rev. 2014-02-24 |
| 3 | Liquid volume, metric | L/d = mg/L x m³/d / (strength x density kg/L x 1,000) | EOCP |
| 4 | Pump rate, metric | mL/min = m³/d x mg/L / (density g/cm³ x strength x 1,440) | EOCP |
| 5 | Pump rate, US | mL/min = MGD x mg/L x 3.785 L/gal x 1,000,000 gal/MG / (strength mg/mL x 1,440 min/d) | Florida DEP |
| 6 | Feeder setting | % = desired feed rate / maximum feed rate x 100 | Florida DEP |
Every formula and constant on this page is checked against operator-certification and regulatory sources; see our methodology and fact-checking process.
How Do You Calculate a Chemical Feed Rate? 5 Worked Examples#
A chemical feed rate is calculated from the dose and its basis, the flow, and the product's strength and density. The 5 worked examples below state every input.
| # | Chemical | Inputs | Result |
|---|---|---|---|
| 1 | sodium hypochlorite | 8.5 mg/L as NaOCl; 2,500 m³/d (0.66 MGD); 12.0 wt %; 1.19 kg/L | 21.25 kg/d (46.8 lb/day) NaOCl; 148.8 L/d (39.3 gal/d); 6.2 L/h; 103.3 mL/min |
| 2 | hypochlorite as Cl2 | 2.0 mg/L as Cl2; 10 MGD (37,854 m³/d); 12.5 trade % = 125 g/L = 1.04 lb Cl2/gal | 166.8 lb/day (75.7 kg/d) Cl2; about 160 gal/d (606 L/d); 421 mL/min |
| 3 | aluminum sulfate (alum) | 100 gpd liquid alum; SG 1.33; 48.5 %; 9.5 % Al2O3; 10 MGD | 13.3 mg/L as product; 6.45 as dry alum; 1.26 as Al2O3; 0.67 as Al |
| 4 | sodium hydroxide (caustic soda) | 10 mg/L as NaOH; 10,000 m³/d (2.64 MGD); 50 %; 1.52 g/mL (760 g/L) | 100 kg/d (220 lb/day) NaOH; 132 L/d (34.8 gal/d); 5.5 L/h |
| 5 | pump setting (any liquid) | pump 21 gal/d (79.5 L/d); 15 gal/d (56.8 L/d) wanted | 71.4 % setting; 80 % stroke rate x 90 % stroke length = 15.12 gal/d |
1. Sodium Hypochlorite Feed Rate in L/d and L/h (Metric)#
Worked example: 8.5 mg/L as NaOCl at 2,500 m³/d (0.66 MGD) with 12.0 % NaOCl solution at 1.19 kg/L needs 21.25 kg/d (46.8 lb/day) of NaOCl, which is 148.8 L/d (39.3 gal/d), 6.2 L/h or 103.3 mL/min of solution (EOCP Math for Operators).
2. Hypochlorite as Cl2 in lb/day and gal/d (US): the Trade-Percent Trap#
Worked example: 2.0 mg/L as Cl2 at 10 MGD (37,854 m³/d) needs 166.8 lb/day (75.7 kg/d) of available chlorine, which is about 160 gal/d (606 L/d) or 421 mL/min of 12.5 trade % hypochlorite at 1.04 lb Cl2 per gallon. A 12.5 trade % product holds 125 g/L, or 11.23 wt % NaOCl (Olin Sodium Hypochlorite Handbook, Table 1). Reading it as 12.5 wt % (1.18 lb/gal) sets the pump about 12 % low.
3. Liquid Alum: One Pump Rate, Three Dose Bases#
Worked example: 100 gpd of liquid alum (specific gravity 1.33, 48.5 % solution, 9.5 % Al2O3) fed into 10 MGD is a dose of 13.3 mg/L as product, 6.45 mg/L as dry alum and 1.26 mg/L as Al2O3 (NJAWWA operator dosage presentation, 2021). As aluminum it is 0.67 mg/L (1.26 x 0.529, calculated), so a dose without its basis is ambiguous.
4. Caustic Soda (50 %) Feed Rate in L/h#
Worked example: 10 mg/L as NaOH at 10,000 m³/d (2.64 MGD) needs 100 kg/d (220 lb/day) of NaOH, which is 132 L/d (34.8 gal/d) or 5.5 L/h of 50 % caustic soda, because 50 % NaOH at 1.52 g/mL holds 760 g per liter (6.34 lb/gal). The same dose adds 12.5 mg/L of alkalinity as CaCO3 (EPA OCCT manual, 2016).
5. Dosing Pump Setting: Stroke Rate and Stroke Length#
Worked example: a pump rated 21 gal/d (79.5 L/d) that must deliver 15 gal/d (56.8 L/d) runs at a feeder setting of 71.4 %, set as 80 % stroke rate and 90 % stroke length, which delivers 15.12 gal/d (pump manufacturer instructions). The setting sequence is listed below.
- Set stroke length to 100 %.
- Coarse-adjust stroke rate.
- Fine-adjust stroke length; verify with a calibration cylinder.
Feeders never run below 20 % of maximum, or 10 % with two independent adjustments (Recommended Standards for Water Works, 2022 edition, 5.3 g); pump types are covered under chemical dosing pumps.
How Is the Dose Basis Converted: As Product, As Active or As Ion?#
The dose basis is converted by multiplying with the mass fraction of the counted species, for example as Al = as Al2O3 x 0.529. NSF/ANSI/CAN 60 maximum use levels are as product, so results convert back before the check.
The calculator converts between dose bases with the following factors.
| From | To | Factor | Source |
|---|---|---|---|
| as product | as active | x purity (decimal) | Florida DEP |
| as Al2O3 | as Al | x 0.529 (53.96/101.96) | molar masses (calculated) |
| as PO4 | as P | x 0.326; P to PO4 x 3.066 | molar masses |
| FeCl3 | as Fe | 34.4 % Fe (55.85/162.20) | molar masses |
| wt % NaOCl | available chlorine (as Cl2) | x 0.952 (70.90/74.44) | molar masses; Olin Table 1 |
| trade % hypochlorite | g/L available chlorine | x 10 | Olin Table 1 |
| NaF, Na2SiF6, H2SiF6 | as F | x 0.452, 0.607, 0.792 | CDC Water Fluoridation Principles and Practices |
| Ca, Mg | as CaCO3 | x 2.5, x 4.12 | Florida DEP; Veolia ch. 40 |
| meq/L (epm) | as CaCO3 | x 50.0 | Veolia Table 40-2 |
| gpg | mg/L as CaCO3 | x 17.1 | Florida DEP |
| ppm (mass ratio) | mg/L | x density (kg/L) | Veolia ch. 40 |
ppm vs mg/L: When Are They Equal?#
ppm equals mg/L only when the solution density is about 1 kg/L, because ppm is a mass ratio and ppm x density = mg/L (Veolia Water Technologies Handbook, chapter 40). At 1.52 g/mL, 1 ppm by weight equals 1.52 mg/L (calculated).
Hardness degrees and other unit pairs sit in the water treatment unit converter.
Which Dosing Calculations Does the Tool Cover?#
The tool covers 9 dosing calculations, from dose to feed rate and pump setting to fluoridation, calibration checks and lime-softening doses, compared below.
| # | Mode | Formula | Owner page |
|---|---|---|---|
| 1 | Dose to feed rate | formula rows 1 to 5 above | water treatment chemicals hub |
| 2 | Pump setting | % = desired / maximum x 100; stroke rule | chemical dosing pumps |
| 3 | Chlorination | dose = demand + residual | drinking water disinfection |
| 4 | Dechlorination | residual x ratio (+ 10 % excess); SO2 0.90 by stoichiometry | dechlorination chemicals; sulfur dioxide |
| 5 | Fluoridation | mg/L x MGD x 8.34 / (AFI x purity) | fluorosilicic acid |
| 6 | Cooling and closed loop | lb/day = ppm x blowdown gpm x 0.012; kg/d = ppm x m³/h x 0.024; slug = volume x ppm; half-life 0.693 V/BD | cooling tower water treatment |
| 7 | Calibration check (reverse) | lb/day = g x 1,440 / (454 x min); mg/L = lb/day / (8.34 x MGD) | chemical feed systems |
| 8 | Solution make-up and dilution | mixture % = (V1 C1 + V2 C2) / (V1 + V2); hypochlorite dilution; polymer % = dry lb x 100 / (dry lb + water lb); jar stock 1 mL of 1 % in 1 L = 10 mg/L | coagulants (jar stock); flocculants (polymer make-down) |
| 9 | Alkalinity and lime softening | dose = alkalinity change / alkalinity per mg/L; quicklime = (A + B + C + D) x 1.15 / purity (hydrated lime: 74 for 56); returns no dose for a target pH | hydrated lime |
Chlorine Dose, Chlorine Demand and Residual#
Chlorine dose equals chlorine demand plus the target residual: a 1.5 mg/L demand and a 0.5 mg/L residual need 2.0 mg/L as Cl2 (Florida DEP formula table, 2014; illustrative inputs).
US drinking-water residuals are capped by the MRDL of 4.0 mg/L as Cl2 (40 CFR 141.65, running annual average), which the calculator flags. Demand is read from the breakpoint curve explained under chlorine demand.
Dechlorination Dose: SO2, Bisulfite, Metabisulfite and Thiosulfate Ratios#
Dechlorination dose equals the chlorine residual times the reagent ratio, plus 10 % excess, with the ratios compared below.
| Reagent | Theoretical, mg per mg Cl2 (Recommended Standards for Wastewater Facilities, 2014 edition, section 103) | Field at pH 7.0 (AWWA Manual M20) |
|---|---|---|
| sulfur dioxide (SO2) | 0.9 | 0.99 |
| sodium bisulfite | 1.46 | 1.61 |
| sodium metabisulfite | 1.34 | 1.47 |
| sodium sulfite | 1.78 | 1.96 |
| sodium thiosulfate | 0.56 | 1.9 |
Worked example: a 0.2 mg/L residual plus a 2.0 mg/L margin at 6,700 m³/d (1.77 MGD) needs 14.7 kg/d (32.4 lb/day) of SO2 (EOCP). Reverse osmosis plants dose metabisulfite at about 3.0 mg/mg (DuPont FilmTec Reverse Osmosis Technical Manual).
Fluoride Feed Rate for Water Fluoridation#
Fluoride feed rate equals dose x MGD x 8.34 / (available fluoride ion x purity), with available fluoride ion 0.452 for sodium fluoride, 0.607 for sodium fluorosilicate and 0.792 for fluorosilicic acid (CDC Water Fluoridation Principles and Practices).
Worked example: 0.5 mg/L as F at 1 MGD (3,785 m³/d) from 23 % fluorosilicic acid needs 22.9 lb/day (10.4 kg/d), about 2.7 mg/L as product, below the most common NSF/ANSI/CAN 60 MUL of 5 mg/L as product (NSF listings, 2026-10-21). Feed points are covered under water fluoridation chemicals.
Cooling Tower and Closed-Loop Feed: Blowdown-Paced and Slug Doses#
Cooling-tower inhibitor feed equals the target product ppm x blowdown flow: 100 ppm at 100 gpm (22.7 m³/h) of blowdown needs 120 lb/day (54.5 kg/d) of product (calculated).
A first fill or closed loop takes a slug of system volume x ppm: 100 m³ at 100 mg/L takes 10 kg (22 lb). Blowdown flows come from the cooling tower water balance calculator.
Checking the Actual Dose from a Feeder Calibration#
The actual dose follows from a measured feed: a dry feeder that delivers 500 g in 5 minutes feeds 317 lb/day (144 kg/d), which into 5 MGD (18,925 m³/d) is 7.61 mg/L as product (Florida DEP formula table; calculated).
For liquids, the drawdown runs the pump formula backward: 421 mL/min of 125 g/L product into 10 MGD returns 2.0 mg/L as Cl2. Calibration columns belong to chemical feed systems.
What Limits Does the Calculator Check? Pump Range, Strength and NSF 60 Use Levels#
The calculator checks 8 limits on every result, from the 20 % pump turndown to the NSF/ANSI/CAN 60 maximum use level, the 4.0 mg/L chlorine MRDL and the 4.0 mg/L fluoride MCL.
The maximum use level (MUL) is product-specific, so the user enters it from the listing. Sodium bisulfite listings, for example, are most commonly 46 mg/L as product (162 of 386 product-function rows, NSF listings, 2026-10-21). How use levels are read is explained under NSF/ANSI/CAN 60.
The calculator checks the following 8 limits and shows a warning, never a block.
| # | Check | Threshold | Source |
|---|---|---|---|
| 1 | Pump turndown | below 20 % of maximum output (10 % with two independent adjustments) | Recommended Standards for Water Works, 2022 edition, 5.3 g |
| 2 | Stroke range | stroke rate 10 to 100 %, stroke length 20 to 100 % | pump manufacturer manual |
| 3 | Strength and density | strength above 100 %; hypochlorite density outside 1.134 to 1.258 g/mL (9.00 to 16.70 wt %); message "trade % is g/L / 10, not wt %" | Olin Table 1 |
| 4 | NSF/ANSI/CAN 60 | dose as product above the entered MUL (as product, all application points) | NSF listings |
| 5 | Day tank and storage | day tank above 30 h at average demand; storage below 30 days or below 1.5 times the tanker delivery truck volume | Recommended Standards for Water Works, 2022 edition, 5.5.9 a and 5.5.11 c |
| 6 | Chlorine residual (drinking water) | above 4.0 mg/L as Cl2 (MRDL, 40 CFR 141.65, running annual average) | eCFR |
| 7 | Fluoride target | above 4.0 mg/L (MCL, 40 CFR 141.62); above 2.0 mg/L (SMCL, 40 CFR 143.3) | eCFR |
| 8 | Polymer solution | dry polymer solution above 1 % | Veolia handbook, chapter 35 |
Where Does the Dosage Calculator Fit Among Water Treatment Calculators?#
The dosage calculator is the feed-rate tool among the site's water treatment calculators, next to the scale, water balance, CT, corrosion, glycol and unit tools.
All water treatment calculators show their equation and source; scale tendency after an alkalinity dose sits in the Langelier saturation index calculator.
The CT value calculator, corrosion rate calculator and glycol freeze point calculator cover disinfection credit, coupons and antifreeze.
Jar Test Doses and Stock Solutions#
A jar-test dose converts to a plant dose one to one when both are stated as product; 1 mL of a 1 % stock in a 1 L jar equals 10 mg/L.
Procedure and interpretation belong to the jar test page.
pH Adjustment and Lime Softening Doses#
pH adjustment doses are calculated here from the alkalinity change: 20 mg/L of added alkalinity needs 16 mg/L as NaOH, because each mg/L of caustic soda adds 1.25 mg/L as CaCO3 (EPA OCCT manual).
Excess lime belongs to lime softening, and acids and alkalis are compared under pH adjustment chemicals.
Is 1 mg/L the same as 1 ppm?#
Yes in dilute treated water: 1 mg/L equals 1 ppm when the solution density is about 1 kg/L, and the two diverge in concentrated products, dense sludges and glycol loops (ppm x density = mg/L).
How do you convert mg/L to ppm for a chemical product?#
Divide mg/L by the density in kg/L: for a solution at 1.52 kg/L, 1.52 mg/L is 1 ppm by weight, and for water at about 1 kg/L the numbers are equal.
How do you calculate a dosing rate in ppm?#
Divide the pounds fed per day by 8.34 x MGD, or the grams fed per day by the m³/d treated: 166.8 lb/day of chlorine into 10 MGD is 2.0 ppm (mg/L) as Cl2.
Who Supplies Treatment Chemicals and Dosing Programs?#
Treatment chemicals come from manufacturers, blenders and distributors, and dosing programs from program providers; a quote request states the chemical, strength, basis and daily feed.
Supplier types are compared under water treatment chemical suppliers, and a full dosing program is bought from a water treatment program provider.