Chlorine Dosing Calculator
Enter your pool volume, current and target free-chlorine readings, and the product you’re using, to estimate how much to add. Guidance only — always confirm against your product’s label and re-test afterward.
Chlorine to add
How the dose is calculated
Free-chlorine ppm is a concentration — milligrams of active chlorine per liter of water — so raising it by a fixed amount takes more chlorine in a bigger pool. The calculator converts your pool volume to liters, multiplies by the ppm increase you want to a get a target mass of active chlorine, then divides by your product’s percentage of available chlorine to find how much of the actual product (which is diluted or blended with other ingredients) you need to add.
Liquid products are reported in fluid ounces (and gallons for larger doses); granular products like cal-hypo and dichlor are reported by weight in ounces and pounds, since that’s how they’re measured and sold.
Frequently Asked Questions
What free chlorine level should I be targeting?
CDC: "The typical range is 1-4 ppm for chlorine", and it says to follow the manufacturer's instructions for your product. A shock or superchlorination dose goes higher only as far as your product label allows (this calculator refuses targets above 10 ppm), and nobody swims until a test shows the level is back inside the range the label allows. Always check the guidance for your pool type and your local health authority.
Why does the chlorine product I use matter?
Different chlorine products carry a different percentage of 'available chlorine' by weight — a 12.5% liquid chlorine solution delivers more active chlorine per fluid ounce than a 10% solution, and granular cal-hypo or dichlor carry their own strengths again. This calculator scales the dose to the product's stated percentage, so double-check the % on your specific jug or bag before dosing, since it can vary by manufacturer and even by batch.
Why is my calculated dose different from what my pool store recommends?
This tool uses a standard chemistry-based formula (parts per million as milligrams of active chlorine per liter of water) and a simplifying density assumption for liquid products. Real-world doses can shift slightly with water temperature, sunlight (chlorine breaks down faster in strong UV without stabilizer), and how thoroughly the chemical is mixed in. Treat the result as a solid starting point and re-test with a kit afterward rather than a guaranteed exact figure.
Is it safe to combine chlorine products?
Never mix chlorine products directly with each other or with acids — some combinations can react violently or release dangerous gas. Add one product at a time, always to water (not water to concentrated product), and follow the safety instructions and storage guidance printed on the label.
Dosing guidance only, not a substitute for the manufacturer's instructions or a professional water test. Pool chemicals can be hazardous — read and follow the product label, add chemicals to water (never water to chemical), never mix different products together, and keep them out of reach of children and pets.
Before you add any chemical
- CDC: "Read 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; this could create toxic gases." Never mix different pool chemicals, including different types of chlorine, with each other or with anything else.
- Add the chemical to water, never water to the chemical. CDC: "NEVER add water to the pool chemical because a violent (potentially explosive) reaction can occur."
- Store each chemical separately, closed in its original labeled container, below 95°F (35°C). CDC: "Separate incompatible chemicals (for example, acid and chlorine)." and "Keep chemicals secure and away from children and pets."
- CDC ranges: "The typical range is 1-4 ppm for chlorine" and pH 7.0 to 7.8. Test chlorine and pH before anyone swims, and at least twice a day while the pool is in use (CDC).
- Doses here round DOWN and assume US gallons (a UK gallon is 1.2 US gallons). Add part, circulate, re-test, and keep everyone out of the water until the test reads inside the range.
Pool safety comes first
- Pool Safely (CPSC): "A fence of at least four feet in height should surround the pool or spa on all sides and should not be climbable for children." Fence all four sides, separating the pool from the house, with self-closing, self-latching gates (CDC).
- Pool Safely: "Always watch children when they’re in or near water, and never leave them unattended." Name one adult as the Water Watcher.
- Drain covers: Pool Safely says "never enter a pool or spa that has a loose, broken or missing drain cover." Powerful drain suction "can even trap an adult". Public pools and spas must meet the Virginia Graeme Baker Pool & Spa Safety Act.
- Pumps, heaters and other pool equipment need GFCI protection, and CPSC says to "Have an electrician who is qualified in pool and spa repairs inspect and upgrade your pool, spa or hot tub".
- CDC: hot tub "Water temperature should not be higher than 104°F (40°C)."