Pool shock calculator
Use about 1.1 lbs of cal-hypo shock for a routine shock. Shock at dusk, run the pump overnight, and don't swim until free chlorine is back in range.
Treat this as a starting dose: add less than the full amount when unsure, circulate for a few hours, retest, repeat. Always follow your product's label.
Shocking works only if you add enough — an under-dose won't clear the water or kill the algae, and you'll be shocking again in a day. The calculator above sizes the shock dose to your pool volume and situation so you hit it the first time.
What the calculator needs
Enter your pool volume and the reason you're shocking (routine maintenance, an algae bloom, heavy use, or after a storm), and the tool estimates how much shock product to add. Volume is the key input — an accurate gallon figure is what separates a dose that works from one that falls short. Match the calculator to your shock type (cal-hypo, dichlor, or liquid chlorine), since strengths differ.
Shock harder for algae
The amount depends heavily on the job. Routine shocking uses a moderate dose; clearing a green algae bloom needs a much heavier one, because algae resists normal chlorine levels and a timid dose just wastes product. When in doubt for a bloom, the calculator's higher estimate is the safer bet — under-shocking is the number-one reason algae comes back. Balance pH into range first so the chlorine works at full strength.
Add, circulate, and be patient
Add the calculated shock with the pump running, ideally in the evening so sunlight doesn't burn it off before it works, and run the filter continuously. For a bloom, brush the pool and keep chlorine elevated until the water clears and holds — it typically goes green to cloudy to clear over a day or more. Don't swim until chlorine settles back to the 1–3 ppm range and the water's clear.
Frequently asked questions
How much shock do I need for my pool?
You need pool volume, current free chlorine, target free chlorine, and the strength of the shock product. The calculator estimates the dose, but the product label should control the final amount.
Can I swim right after shocking a pool?
No. Wait until the product label says swimming is allowed and the water tests back in the safe range. If free chlorine is still high, keep the pool closed and retest.
Is liquid chlorine the same as pool shock?
Liquid chlorine can be used for shock treatment, but shock is a treatment goal, not one exact product. Liquid chlorine, cal-hypo, dichlor, and non-chlorine oxidizers dose differently.
Should I shock a green pool once or more than once?
A green pool may need repeated testing, brushing, filtration, and chlorine additions. One bag tossed in once is often not enough if algae is active or the pool volume was guessed wrong.
Should I shock at night?
Many homeowners dose chlorine in the evening because sunlight can reduce chlorine faster during the day. The more important rule is to test, dose safely, circulate, and keep swimmers out until the water is safe.
Embed this calculator (free)
Run a pool site or blog? Drop this tool into any page — it stays free and links back here. Paste this HTML where you want it to appear.
<iframe src="https://www.poolgearguide.com/embed/pool-shock-calculator-how-much-shock-does-your-pool-need" title="Pool Shock Calculator: How Much Shock Does Your Pool Need?" width="100%" height="560" style="border:1px solid #e5e7eb;border-radius:12px;max-width:680px" loading="lazy"></iframe>
