Always test your water with a test kit before adding chemicals. Estimates only. Never mix pool chemicals. Cal-hypo and trichlor/dichlor must NEVER be mixed — contact causes fire hazard.

Pool Shock Calculator

Enter your pool volume, current free chlorine, and target chlorine level to calculate exact shock dosage. Formula verified against Standard Chemicals and the CDC Model Aquatic Health Code guidelines (June 2026).

Pool Shock Inputs

FC targets per Standard Chemicals: 10 ppm routine, 20 ppm cloudy/heavy use, 30 ppm algae.

Shock to Add
—
pounds
1-lb Bags Needed
—
× 1 lb bags
FC Raise
—
ppm

Shock targets per Standard Chemicals: 10 ppm routine, 20 ppm cloudy/heavy use, 30 ppm algae or contamination.

Critical safety: Always pre-dissolve granular cal-hypo in a bucket of pool water before adding to the pool. Never mix cal-hypo with trichlor, dichlor, or any other pool chemical — contact causes a violent exothermic reaction and fire risk. Add shock at dusk or nighttime. Per Standard Chemicals, wait until FC drops below 5 ppm before swimming.

Dosing by Pool Size & Scenario

Pool Size Routine (10 ppm) Cloudy (20 ppm) Algae (30 ppm)

Assumes 68% cal-hypo with no existing free chlorine. Per Standard Chemicals, 1 lb of 68% cal-hypo raises FC by ~7.8 ppm per 10,000 gal. Source: Standard Chemicals pool shock calculator — verified June 2026.

Formula

Lbs = (Target FC − Current FC) × Pool gallons × 8.345 ÷ (Product strength × 1,000,000)
  • Product strength — the available chlorine fraction (0.68 for 68% cal-hypo)
  • 8.345 ÷ 1,000,000 — converts ppm (parts per million by weight) to pounds of pure chlorine per Standard Chemicals shock formula: 1 gallon of water weighs 8.345 lb, and 1 ppm = 1 part per million by weight
  • FC raise — you only add the deficit from current to target

Related calculators: Salt Calculator · Chlorine Calculator · Alkalinity Calculator · Stabilizer (CYA)

Frequently Asked Questions

How much pool shock do I need per 10,000 gallons?

For 68% calcium hypochlorite (cal-hypo), the standard dose is 1 pound per 10,000 gallons, raising free chlorine by approximately 7–8 ppm per Standard Chemicals. For algae treatment, 2–3 lbs per 10,000 gallons is typical.

When should I shock my pool?

Shock after heavy use (swim parties, storms), when free chlorine drops below the CDC minimum chlorine level, when water turns cloudy or green, after opening the pool for the season, and once per week as a preventive measure during peak summer months.

Can I use liquid bleach instead of granular shock?

Yes. Per poolchemcalculators.com, household bleach (6–8.25% sodium hypochlorite) works but requires a much larger volume than pool-grade granular shock. The calculator supports 65% and 73% cal-hypo; for liquid chlorine, use the separate Chlorine Calculator.

Is it safe to swim after shocking?

Per Standard Chemicals shock guidance, wait until free chlorine drops below 5 ppm before swimming. Circulation time varies with sunlight and bather load — always test before allowing anyone to swim.

Should I shock at night or during the day?

Shock at dusk or nighttime. UV from sunlight destroys chlorine rapidly — shocking at night lets the chemical circulate for hours before sunlight degrades it.