Hypochlorous acid is used at very different strengths depending on the job, and the figure printed on a drum is rarely the figure you want in the bucket. This calculator does the arithmetic four ways: how much concentrate a batch at a target strength needs, what a quantity of concentrate you already have will make, what strength a mix you have already made actually is, and how much HOCl to add to a volume of water you already have — a tank, a reservoir or a system — to reach a target strength. It works in millilitres, litres and US gallons, with concentration in mg/L or ppm.
The arithmetic
C1 × V1 = C2 × V2
Strength times volume is the amount of active ingredient, and dilution does not change that amount — it only spreads it through more water.
Treating water you already have: HOCl to add = water volume × C2 ÷ (C1 − C2). The concentrate itself adds to the volume, which is why the divisor is C1 − C2 rather than C1.
ppm and mg/L are the same number here. One milligram in one liter of water is one part per million, because a liter of water weighs very close to one million milligrams. The unit selector changes the label, not the result. It is there so the figure matches whichever way your test kit or supplier reports it.
Volumes are assumed to add up — 250 mL of concentrate into 4.75 L of water gives 5 L. For dilute water-based solutions that holds to far better than you can measure in a bucket.
Before you rely on a number
- Measure the concentrate, do not assume it. Hypochlorous acid loses strength with time, light, heat and headspace. A drum that tested at 200 ppm last month is not 200 ppm today. Test it, then dilute from the figure you measured.
- Dilution changes more than strength. The water you dilute with brings its own pH, hardness and whatever else is in it. Check the pH of the finished solution rather than assuming it carried over.
- Mix into water, and mix it through. A layer of concentrate sitting at the bottom of a tank is not a dilution.
- Small volumes need real measuring. Anything under a few millilitres wants a syringe or a graduated pipette, not a jug.
An EcoloxTech system is a device that produces a hypochlorous acid solution on site. We make no efficacy claims for the device, or for the solution it produces. This calculator performs arithmetic only and does not recommend a concentration for any purpose. Where a documented disinfection claim against a named organism is required, it comes from a registered product used according to its label — HOCl-AS200 (EPA Reg. No. 101112-1).
mg/L and ppm are the same number
In water, one milligram per litre is one part per million, because a litre of water weighs very close to one million milligrams. Test kits, supplier datasheets and labels use the two interchangeably, which causes a surprising amount of doubt. The unit selector above changes the label, not the result. It is there so the figure matches however your own test kit or supplier reports it.
Measure the concentrate rather than trusting the label
Hypochlorous acid loses strength over time, and loses it faster with light, heat and air in the headspace of a part-used container. A drum that tested at 200 ppm when it was filled is not necessarily at 200 ppm today. The arithmetic is exact; the number you feed it is not. Test the concentrate, then dilute from the figure you measured.
What dilution changes besides strength
The water you dilute with brings its own pH, hardness and whatever else is in it, and hypochlorous acid is sensitive to pH. Check the pH of the finished solution rather than assuming it carried over from the concentrate. Mix the concentrate into the water and mix it through as well: a layer of concentrate sitting at the bottom of a tank is not a dilution.
Small volumes need real measuring
At high ratios the amount of concentrate gets small quickly. Two millilitres into two litres is a legitimate dilution, but it wants a syringe or a graduated pipette rather than a jug, because a millilitre out by eye is a fifty per cent error. The calculator flags the cases where this matters.
What this calculator is not
It performs arithmetic. It does not recommend a concentration for any purpose, and it is not a substitute for a product label. An EcoloxTech system is a device that produces a hypochlorous acid solution on site; we make no efficacy claims for the device, or for the solution it produces. Where a documented disinfection claim against a named organism is required, it comes from a registered product used according to its label — HOCl-AS200 (EPA Reg. No. 101112-1).
Related reading
- HOCl system sizing calculator — how many generators a given daily volume needs
- How on-site generation works
- Book a free sanitation audit