Pool Chemical Dosage Calculator
Calculates the exact amount of chlorine needed to bring your pool to a safe level. Use it when opening your pool, after heavy rain, or whenever your test kit shows low chlorine.
About this calculator
This calculator determines how much chlorine to add by first converting your pool's rectangular volume from cubic feet to gallons (1 cubic foot = 7.48 gallons), then scaling the dose to the parts-per-million (ppm) deficit. The core formula is: dose = ((length × width × avgDepth × 7.48) × (targetChlorine − currentChlorine)) / 1,000,000. The division by 1,000,000 converts the raw ppm-gallon product into a practical pound-equivalent dose. A standard safe chlorine range is 1–3 ppm. Knowing your pool's exact volume is critical — under-dosing leaves the water unsafe, while over-dosing can irritate skin and eyes and damage pool surfaces.
How to use
Suppose your pool is 30 ft long, 15 ft wide, and 5 ft deep on average. Your test kit reads 0.5 ppm chlorine and your target is 2.0 ppm. Step 1 — volume in gallons: 30 × 15 × 5 × 7.48 = 16,830 gallons. Step 2 — chlorine deficit: 2.0 − 0.5 = 1.5 ppm. Step 3 — dose: (16,830 × 1.5) / 1,000,000 = 0.025 lbs of active chlorine needed. Always add chemicals with the pump running and retest after 4–6 hours.
Frequently asked questions
How much chlorine do I need to shock a pool after heavy rain?
Heavy rain dilutes chlorine and can introduce contaminants, so shocking is recommended when levels drop below 1 ppm. Use this calculator with your post-rain chlorine reading as the current level and set the target to 3 ppm or higher for a shock dose. Shock treatments typically aim for 5–10 ppm to break down chloramines. Run the pump continuously for at least 8 hours after shocking.
Why does pool volume in gallons matter for chemical dosing?
Chemical dosing is measured in parts per million relative to the total water volume, so a larger pool needs proportionally more chemical to reach the same ppm change. Using cubic feet without converting to gallons would produce a wildly incorrect dose. The factor 7.48 converts cubic feet to U.S. gallons accurately. Even a 10% error in volume estimation can leave your pool over- or under-treated.
What is a safe target chlorine level for a residential pool?
The CDC and most pool professionals recommend maintaining free chlorine between 1 and 3 ppm for residential pools. Levels below 1 ppm are insufficient to kill bacteria and algae effectively. Above 3 ppm, swimmers may experience eye and skin irritation. For pools with higher bather loads or strong sunlight, staying near the upper end of the range offers better protection.