🧪 Chlorine Dosing Calculator
Enter your pool volume, current and target free chlorine, and the product and strength on your label to estimate how much to add. The answer rounds down; the label has the final say.
💧 The Right Dose, Every Time
Before you add any chemical
- Read the whole product label before each use and follow it. The label, not this calculator, sets the dose and the strength (CDC).
- Never mix chlorine products with acid: CDC warns this could create toxic gases. Never mix different pool chemicals, including different types of chlorine, with each other or anything else (CDC).
- Calcium hypochlorite (cal-hypo) and trichlor can react violently, causing fire or explosion (US EPA). Never put one in a feeder, floater or bucket that held the other.
- If the label says to pre-dissolve, add the chemical to water, never water to the chemical: CDC warns a violent, potentially explosive reaction can occur.
- Store each chemical separately in its original labeled container, dry, out of direct sunlight and below 95°F (35°C), in a locked area children and animals cannot reach (CDC).
- CDC ranges: free chlorine at least 1 ppm in pools (at least 2 ppm with cyanuric acid stabilizer) and at least 3 ppm in hot tubs; pH 7.0 to 7.8. Test chlorine and pH before anyone swims.
- After raising chlorine, keep everyone out until a test shows the level the label allows (one EPA-registered liquid chlorine label says below 4.0 ppm).
What is a Chlorine Dosing Calculator?
It tells you how much of a specific chlorine product to add to move your pool's free chlorine from where it is now to where you want it. Give it your volume, the current and target ppm, and your product type, and it applies that product's dosing rate, rounded down, to estimate the amount.
Getting chlorine right is the single most important part of keeping water clear and safe, but the correct amount depends entirely on your pool's size and current reading. This removes the guesswork — dose with the pump running, let it circulate, and always re-test, treating the figure as a planning estimate.
❓ Frequently Asked Questions
What free chlorine level should I aim for?
CDC recommends free chlorine of at least 1 ppm in pools (at least 2 ppm if you use cyanuric acid stabilizer) and at least 3 ppm in hot tubs, with pH 7.0 to 7.8, and testing at least twice a day. Your product label gives its own range. If you raise chlorine higher to shock, the calculator refuses targets above 10 ppm, and nobody swims until a test shows the level the label allows (one EPA-registered liquid chlorine label says below 4.0 ppm).
What's the difference between the chlorine products?
Liquid chlorine (sodium hypochlorite, ~12.5%) adds no stabiliser and slightly raises pH. Cal-hypo (65%) is a strong granular shock but adds calcium hardness. Dichlor (56%) and trichlor (90%) are stabilised — convenient, but they steadily raise cyanuric acid, which can eventually lock up your chlorine, so watch that level over a season.
How does the calculator work out the amount?
Raising 1 ppm in 10,000 US gallons takes 37.85 g of available chlorine. That is about 10.2 fl oz of 12.5% liquid chlorine or 2.0 oz of 65% cal-hypo (each rounded down). The calculator multiplies that by the ppm you are raising and your volume in ten-thousands of US gallons, scales it to the strength on your label, and rounds the answer down, so any error leaves you short rather than over. Re-test and add more if needed.
Can I add too much chlorine?
Yes. Over-chlorinated water can irritate skin and eyes, and nobody should swim until a test shows the level the label allows. Add measured amounts with the pump running, let it circulate, and re-test before adding more. Never mix chlorine products with each other or with acid, add chemicals to water and never water to chemicals, and store each one separately, locked away from children.