About this tool
The Chlorine Dose Calculator is a free, in-browser pool tool that tells you exactly how much of a chosen chlorine product to add to raise free chlorine (FC) from its current level to your target, in parts per million. Enter the pool volume in gallons, the current and target FC, and the product, and it returns the dose by weight (for dry products) or by volume (for liquids), plus the pure chlorine added. All math runs locally in your browser, so nothing you type is uploaded.
The method converts gallons to liters (L = gallons × 3.78541), since 1 ppm = 1 mg/L. Pure chlorine needed in grams is delta_ppm × L / 1000. For dry products the amount of product is pure_g ÷ (available-chlorine fraction) — cal-hypo at 65% or 73%, dichlor 56%, trichlor 90%, or lithium hypochlorite 35%. For liquid sodium hypochlorite the volume is pure_g ÷ trade%, because trade percent already means grams of available chlorine per 100 mL: 12.5% pool liquid or 10% household strength. Weights convert to ounces and pounds, volumes to fluid ounces and cups.
As a worked example, raising a 10,000-gallon pool by 2 ppm needs about 75.7 g of pure chlorine. That is roughly 606 mL (about 20.5 fl oz) of 12.5% liquid chlorine, or about 116 g (4.1 oz) of 65% cal-hypo. Always add chlorine to a bucket of water (never the reverse), broadcast it with the pump running, and re-test before swimming; the tool assumes a well-mixed pool.