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.
Last updated: May 2026
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.