pool Pool Volume & Chlorine Calculator star

How It's Calculated

Everything starts with volume, and volume starts with average depth — take the shallow end and the deep end, add them, divide by two. A rectangular pool is then simply length × width × average depth. Round pools use π·r² × depth, and ovals are approximated as ≈0.89 × length × width × depth (the 0.89 factor accounts for the rounded ends eating into what would otherwise be a rectangle). Pools with steps or a shallow shelf need to be broken into two or three simpler shapes and summed — the calculator handles the standard shapes, but the same average-depth logic applies to each section.

Worked example: an 8 × 4 m rectangular pool averaging 1.5 m deep holds 8 × 4 × 1.5 = 48 m³, or 48,000 liters (≈12,680 US gallons). That volume is the number every chemical calculation keys off.

Chlorine dosing follows directly from volume because the units are built for it: 1 ppm (part per million) of chlorine equals 1 gram of pure chlorine per cubic meter. Raising 48 m³ by 2 ppm needs 48 × 2 = 96 grams of pure available chlorine. Almost no product is 100% pure, though — granular calcium hypochlorite ("cal-hypo") runs 65-70% available chlorine, so 96 g pure ÷ 0.65 ≈ 148 g of actual granules. The same 96 g target takes about 107 g of 90%-strength trichlor, or roughly 770 g of 12.5% liquid bleach, since the math always divides the pure-chlorine requirement by the product's labeled concentration.

• Trichlor tablets: ~90% available chlorine, also lowers pH (acidic) — good for slow-release feeders, not shocking.
• Dichlor granules: ~56-62%, pH-neutral, dissolves fast — common for shocking smaller pools.
• Calcium hypochlorite (cal-hypo): ~65-70%, raises calcium hardness over time, the classic shock treatment.
• Liquid chlorine / bleach: ~10-12.5%, cheap and pH-neutral but degrades in storage — buy it fresh.

What You Should Know

Getting the dose right matters in both directions. Too little chlorine leaves the pool under-protected: algae takes hold within a day or two in warm weather, and pathogens are not reliably neutralized. Too much chlorine is its own hazard — concentrations much above 5 ppm irritate skin, eyes and respiratory passages, bleach hair and swimwear, and accelerate corrosion of pumps, heaters and ladders. The dosing formula tells you how much product to add, but it cannot replace a water test: always confirm the actual free chlorine level with test strips a few minutes after adding chemicals, since wind, sunlight and bather load all shift the real-world result.

Two companion numbers decide how well that chlorine survives. Cyanuric acid (stabilizer) at 30-50 ppm shields free chlorine from UV breakdown — without it, direct sun can burn off most of the day's dose within hours. Push past roughly 100 ppm of stabilizer, though, and it starts locking chlorine into a less active state ("chlorine lock"), and the only fix is a partial drain and refill. pH is the other lever: keep it in the 7.2-7.6 range, because chlorine grows sluggish and far less effective as pH climbs above that band, even when the ppm reading looks fine.