Chemical dosing becomes much easier when the calculation is separated into three questions: how much active chemical is required, how much commercial product contains that active chemical, and what volumetric pump rate will deliver it. This method works for many water-treatment products, including sodium hypochlorite, acids, alkalis, antiscalants and formulated treatment chemicals.
1. Start with flow and target dose
For dilute water systems, 1 ppm is approximately 1 mg/L. If the water flow is in m³/hr and the dose is in ppm, the pure chemical requirement is:
Pure chemical, kg/hr = Flow (m³/hr) × Dose (ppm) ÷ 1000
Example: for 100 m³/hr at 5 ppm, pure chemical = 100 × 5 ÷ 1000 = 0.50 kg/hr.
2. Correct for commercial concentration
Most chemicals are not supplied as 100% active product. If the supplied chemical is 35% w/w:
Commercial product, kg/hr = Pure chemical kg/hr ÷ 0.35
For the example above, 0.50 ÷ 0.35 = 1.429 kg/hr.
3. Convert kg/hr to L/hr
Dosing pumps are normally selected by volume. Use the product density from the current supplier SDS or TDS:
Product L/hr = Product kg/hr ÷ Density (kg/L)
If density is 1.18 kg/L, the required pump delivery is 1.429 ÷ 1.18 = 1.211 L/hr.
4. Estimate daily and monthly consumption
If the plant operates 24 hours/day, daily product consumption is 1.429 × 24 = 34.29 kg/day. For 30 operating days, monthly consumption is approximately 1,029 kg/month.
Common mistakes
- Using the product concentration as if it were 100% active.
- Ignoring density when converting kg/hr to L/hr.
- Using nominal plant flow when the actual operating flow varies significantly.
- Assuming a ppm target is valid without checking water analysis, process demand and supplier recommendations.
- Sizing the pump exactly at the calculated duty with no practical operating margin or turndown consideration.
Use the Ramven calculator
You can perform the same calculation on the Ramven Chemical Dosing Calculator. Treat the result as an engineering estimate and verify the actual product concentration, density, pump back-pressure, chemical compatibility and site safety requirements before implementation.
Safety note: chemical dosing should follow the product SDS, site procedure and applicable safety requirements. Never mix incompatible chemicals or make concentration changes without reviewing hazards and equipment compatibility.