Pool Shock Calculator
Enter your pool volume, test your current free-chlorine level, pick your target ppm and shock product — get the exact dose to add safely and effectively.
Unit system
gal
ppm
ppm
Shock product
Amount of the selected shock product needed to reach the target chlorine level
- 1
Chlorine increase needed
10 − 0 = 10 - 2
Pool volume in litres
15,000 × 3.7854 = 56,781.2 - 3
Pure chlorine (kg)
56,781.2 × 10 ÷ 1 000 000 = 0.567811 ppm = 1 mg/L; mass (kg) = volume (L) × ppm ÷ 1 000 000. - 4
Product to add (lbs)
0.56781 ÷ 0.73 × 2.20462 = 1.71
How does this calculator work?
Pool shock dose = Pool volume (L) × (Target − Current) ppm ÷ 1 000 000 ÷ available-chlorine fraction. A 73% cal-hypo shock needs about 1 lb per 10 ppm rise in 10 000 gallons. Always test water first, shock at night, and wait until chlorine drops below 3 ppm before swimming. Never mix different shock chemicals.
Formula
How this is calculated
Pool shock raises the free-chlorine concentration above a breakpoint (typically 10 ppm) to destroy chloramines, algae, and bacteria. Because different shock products contain different percentages of "available chlorine" — the active ingredient that sanitises — the dose must be adjusted for each product type.
The core formula: the mass of pure chlorine needed equals pool volume in litres times the desired concentration increase in ppm (mg/L) divided by 1 000 000 (unit conversion). Dividing by the product's available-chlorine fraction gives the mass of product to add. For US users, pool volumes are converted from gallons (1 gal = 3.785 L) and mass from kg to lbs or fl oz for liquids.
Concentration values used here are typical for each product class: calcium hypochlorite ~73%, Dichlor ~56%, Trichlor ~90%, liquid sodium hypochlorite ~10–12%. Always read your specific product label, as concentrations vary by brand and can degrade over time in storage. Add shock to the pool in the evening or at night to minimise UV breakdown, pre-dissolve granular products in a bucket of water, and do not swim until free chlorine drops below 3 ppm.
Frequently asked questions
Breakpoint chlorination is the point at which enough chlorine has been added to completely oxidise chloramines (combined chlorine), leaving only free chlorine. It typically requires adding 10 times the combined-chlorine reading. This calculator uses a target ppm approach — set your target to 10 ppm for a standard shock.
Shock after heavy use, storms, visible algae, or when the water smells of chloramines (the "chlorine smell" is actually combined chlorine, not free chlorine). Routine: every 1–2 weeks in summer, or when free chlorine is below 1 ppm.
Never mix different shock products together — some combinations (e.g. calcium hypochlorite + Trichlor) react violently and can cause fire or explosion. Add each product separately directly to the pool, one at a time.
Also known as
TG we-Calculate Editorial Team. (2026). Pool Shock Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/pool-shock-calculator
TG we-Calculate Editorial Team. "Pool Shock Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/pool-shock-calculator.
TG we-Calculate Editorial Team, "Pool Shock Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/pool-shock-calculator
@misc{wecalculate_pool_shock_calculator, title = {Pool Shock Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/pool-shock-calculator}}, year = {2026}, note = {TG we-Calculate} }
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