Pool Shock Calculator
Enter free chlorine (FC) and combined chlorine (CC) from your test. The standard rule is to add about 10 times the combined chlorine. Or set your own target.
Quick answer: The standard rule is to add 10 times your combined chlorine. For a 10,000-gallon pool with 0.5 ppm combined chlorine, that's 5 ppm, or about 10 oz of 65% cal-hypo shock.
Checked against 5 published sources (see them). Updated October 2026.
- Raises free chlorine to about
- 7.0 ppm
- Adds 6.0 ppm.
- Swim again when
- FC is 4 ppm or less
- Or the level your product label allows.
How it works
Combined chlorine (CC) is chlorine that has already reacted with sweat, urine and other waste. It causes the "pool smell" and irritates eyes. The CDC's Model Aquatic Health Code says to act when it's above 0.4 ppm.
The standard rule (called breakpoint chlorination) is to add about 10 times the combined chlorine as free chlorine. With 0.6 ppm combined chlorine, that means adding about 6 ppm.
Guidance on shock levels varies between sources, and product labels differ. If your label gives a different amount, follow the label. Shock at dusk with the pump running, since sunlight burns chlorine off.
Tips
- Shock in the evening and run the pump overnight. Retest in the morning.
- Cal-hypo adds calcium; dichlor adds stabilizer (CYA). Liquid chlorine adds neither.
- Don't swim until free chlorine is back down to 4 ppm or the level on your product label.
Sources
We checked the math on this page against:
- CDC Model Aquatic Health Code, 2024 edition
- Indiana Department of Health: How to Shock the Pool
- Lucas County (Ohio) Health Department: Pool Chemistry Adjustments
- Indiana Department of Health: Adjusting Chemical Levels in a Swimming Pool
- Pool & Hot Tub Alliance fact sheet: Sodium Hypochlorite
Frequently asked questions
How much shock do I need?
Test free and combined chlorine. Add about 10 times the combined chlorine. For 15,000 gallons with 0.6 ppm combined chlorine, that's about 6 ppm, or roughly 19 oz (1 lb 3 oz) of 65% cal-hypo.
My pool is green. How much shock?
Green water needs much more chlorine than the 10× rule, held for longer, and guidance varies. Choose "Raise to a level I choose", follow your shock product's label, and retest often.
When can I swim after shocking?
When free chlorine is back to 4 ppm or less, or the level your product label allows.