Pool Chlorine Dose Calculator

The dose is the transparent industry identity. Each pound of pure available chlorine raises free chlorine (FC) by a fixed amount per 10,000 gallons, because one US gallon of water weighs about 8.3454 lb. We compute the pure-chlorine mass for your FC raise, then divide by the product's available-chlorine percent to get the amount you actually scoop or pour, then convert to your chosen unit.

ΔFC        = max(0, target FC − current FC)        (ppm)
pure_lb    = volume_gal × ΔFC × 0.0000083454       (lb pure chlorine)
product_lb = pure_lb ÷ (strength% ÷ 100)

liquid / bleach:  fl oz = product_lb ÷ 9.7 × 128   (cups ÷8, qt ÷32, gal ÷128)
cal-hypo / dichlor: oz = product_lb × 16           (show lb at ≥ 1 lb)
trichlor:         tabs = ceil(product_lb × 16 ÷ tab_oz)

side effects (added per ΔFC ppm):
  dichlor            → CYA  ≈ 0.9 × ΔFC ppm
  trichlor           → CYA  ≈ 0.6 × ΔFC ppm
  cal-hypo           → CH   ≈ 0.7 to 0.8 × ΔFC ppm  (pure → packaged product)
  liquid / bleach    → pH   ≈ 0.2 × ΔFC units
suggested target FC ≈ 0.075 × current CYA

The 0.0000083454 constant is 8.3454 lb/gal ÷ 1,000,000; it matches Calculator Academy's published oz = (V × ΔFC) / 7500 within rounding. The liquid conversion folds a sodium-hypochlorite solution density of about 9.7 lb/gal into one factor rather than asking you for density. Calcium hardness is shown as a range (0.7–0.8 × ΔFC) with a bound at each end rather than a hedge. Pure calcium hypochlorite releases two chlorines and one calcium per molecule, and hardness is reported as calcium-carbonate equivalent, so 100.09 ÷ (2 × 70.906) = 0.71 is a floor. Available chlorine comes only from the hypochlorite while calcium can also arrive as other calcium salts in the packaged product, which is why APSP's published figure for real product — 8 ppm of hardness per 10 ppm of available chlorine — sits above it. The two CYA ratios are not a range and not interchangeable: each isocyanurate molecule carries exactly one cyanurate ring, so dichlor's two chlorines drag half again as much stabiliser per ppm of free chlorine as trichlor's three. From the molar masses — cyanuric acid 129.07 g/mol, chlorine 70.906 g/mol as Cl₂ — that is 0.91 for dichlor and 0.61 for trichlor, and APSP publishes the same 6-ppm-per-10-ppm trichlor figure. Doses are pourable estimates, not lab accuracy: sunlight, bather load, and contaminants consume chlorine, so your measured result will differ.

A measured pour is only one of the ways chlorine reaches a pool. When the trichlor goes in as tabs in a feeder or floater instead, the weekly count is worked out on the chlorine tablet calculator from the registered label rate or your own measured loss. If free chlorine keeps reading fine while the water still smells and stings, the gap between free and total is combined chlorine, and clearing it takes the much larger oxidizing dose sized on the breakpoint chlorination calculator rather than another routine dose here.

Sources: Calculator Academy — Pool Chlorine Calculator; Clean Pool Math — Pool Chlorine Calculator; Pool & Spa News — ppm unit of measure; My Pool Calculator — chlorine dose; The Pool Nerd — FC = 7.5% of CYA. CYA ratios: molar masses from PubChem (cyanuric acid CID 7956; sodium dichloroisocyanurate CID 517202; trichloroisocyanuric acid CID 6909), with trichlor cross-checked against APSP via Aquatics International.