Pool Shock Calculator

Shock dosing is an available-chlorine mass balance: the product amount scales with your pool volume, with how far you need to raise free chlorine (Δppm), and inversely with the product's available-chlorine %.

combined chlorine (CC) = total chlorine − free chlorine   (breakpoint mode)

target FC, by basis:
  breakpoint:  10 × CC      (the 10:1 breakpoint rule; 10 ppm if TC unknown)
  reason:      routine 10 · opening 15 · light algae 20 · heavy algae 30 · after-rain 15
  custom:      the FC ppm you enter

Δppm = max(0, target FC − current FC)

dose = Δppm × (volume / 10,000) ÷ (ppm-per-unit × strength factor)
     ≈ cal-hypo 65%  2.05 oz per ppm per 10k
     ≈ liquid 10%    12.8 fl-oz per ppm per 10k

Strength is the biggest lever. A 12.5% jug of liquid raises FC faster than a 10% jug, so the same dose target needs less product — the tool divides the dose by your entered strength relative to each chemical's reference (cal-hypo 65%, liquid 10%, dichlor 56%, lithium 35%).

This is a shock dose, not maintenance. Our cal-hypo basis is the better-corroborated shock figure (about 7.8 ppm FC per pound of 65% cal-hypo in 10,000 gallons — Larry's Pool's "≈ 20 oz for +10 ppm" and Omni's coefficient), which differs slightly from a routine-maintenance basis. Treat the number as a starting dose and re-test with your kit.

Sources: Omni Calculator — Pool Shock Calculator (breakpoint math + safety envelope); Larry's Pool — Pool Shock Calculator (five chemistries + CC-unknown fallback); The Pool Nerd — Pool Shock Calculator (reason → target ppm).