Water & Containers

Pool Shock Calculator

Compare dry cal-hypo product mass for a concentration change you supply.

Units

Your measurements

Results update as you type.

Pool volume

Current free chlorine (ppm)

Enter a measured free-chlorine result, not total chlorine. Check the test kit range: a high chlorine concentration can cause a falsely low DPD reading. Supported arithmetic input range only: 0–100 ppm, with target above current. Being within this software range does not make a target suitable or safe.

Target free chlorine (ppm)

Enter a target justified by the exact product label and qualified pool-care advice. No shock target is selected here. Supported arithmetic input range only: 0–100 ppm, with target above current. Being within this software range does not make a target suitable or safe.

Available chlorine by mass (%)

Enter labelled AVAILABLE CHLORINE by mass, not calcium-hypochlorite ingredient percentage. This model is for dry cal-hypo, not liquid chlorine or non-chlorine shock.

Fractions and number formats

Use decimals (12.5), fractions (12 1/2 or 12-1/2), or explicit lengths (12ft 6in, 12′ 6″, 25 mm). A comma followed by one or two digits is a decimal comma: 12,5 = 12.5. Grouped commas mean thousands: 1,200 = 1200. Use a decimal point for ambiguous values. Scientific notation is not accepted.

Enter your measurements

Results update as you type.

About this calculator

Estimate dry calcium-hypochlorite product mass from explicitly supplied water volume, current and target free-chlorine concentrations, and labelled available chlorine by mass. The form chooses no target or strength. This theoretical comparison does not account for chlorine demand or establish an application procedure or safe re-entry.

How to use this calculator

Confirm actual water volume and a free-chlorine measurement within the test kit range.
Supply the chosen target from the exact product label and qualified pool-care advice.
Enter the dry product label's available-chlorine mass percentage.
Read the theoretical mass only. Follow the actual product label for handling and application; the result does not determine treatment response or safe swimming conditions.

Formula

Dry product kg = pool litres × increase in ppm ÷ (10,000 × available chlorine %)

oz = kg ÷ 0.45359237 × 16

Assumptions

Dry product mass is a dilute-water mass balance using the labelled available-chlorine mass percentage. Chlorine demand, actual treatment response and safe re-entry are not predicted.
Cyanuric acid, pH and stabilizer levels affect chlorine efficacy but are not modelled.
The pool is at normal water level and fully mixed.
A DPD test may bleach and report falsely low chlorine when the concentration exceeds its useful range. Confirm the test manufacturer's instructions; do not treat a suspect zero as a dosing input.
Supported arithmetic input range only: 0–100 ppm, with target above current. Being within this software range does not make a target suitable or safe.

Common mistakes

Using active ingredient percentage instead of available chlorine.
Entering liquid chlorine into a dry-product mass model.
Treating the calculated addition as a safe-swimming or application instruction.

Worked example

Try it: press “Load example” above the form.

Illustrative arithmetic only: 20,000 US gal, a user-chosen increase from 1 to 10 ppm, and a supplied 65% available-chlorine value correspond to about 1.048 kg (36.977 oz) of dry product. These values do not recommend a target, brand or treatment procedure.

Limitations

Educational dry-product mass comparison only, using the available-chlorine percentage on your actual cal-hypo label. This tool does not choose a shock target, predict treatment response or determine when swimming is safe. Never mix pool chemicals.

Frequently asked questions

Is this for liquid chlorine?

No. It estimates dry calcium-hypochlorite product mass from available chlorine by weight. Liquid chlorine requires density and a matched concentration basis; non-chlorine shock is a different product.

Does this tell me when swimming is safe?

No. The chosen target and mass calculation do not measure chlorine demand, pH or safe re-entry. Follow the exact product label, test the water and obtain qualified pool-care advice when needed.

What does the worked example show?

Which assumptions should I check before using the result?

Dry cal-hypo mass calculation only. Does not determine a shock target, chlorine demand, cyanuric-acid adjustment, application procedure or safe swimming conditions. Never mix pool chemicals. Follow the exact registered label.

Reviewed by Codex AI editorial agent (Editorial, 2026-11-12) · Codex independent specialist-review AI agent (educational arithmetic/source review; not licensed human approval) (Pool-chemistry, 2026-11-12).

Sources

Sources explain the methods and any named product presets. Check your product label where coverage, yield or density differs.

US EPA: Westlake 70% calcium-hypochlorite label, accepted 16 July 2025
Named example distinguishing calcium-hypochlorite ingredient percentage from available chlorine by mass. It is not the user's product label or a universal treatment recommendation.
NIST: Revised Unit Conversion Factors
CDC: pool chemical safety
Product-specific handling and label directions; does not supply a universal chlorine target, dose procedure or safe re-entry decision.
CDC: home pool water testing
DPD testing-range caveat and the need to follow test-kit instructions. The calculator does not choose a treatment target or determine swimming safety.

Calculation documentation · Updated 2026-11-12 · Version 1.6.4. Estimates are planning aids. Confirm quantities, coverage and prices with your supplier before purchasing. Found an error? Report it.

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