Pool Shock Calculator
Shock level is about 40% of your CYA reading. Enter your pool volume, CYA, and chlorine product to get the dose.
Shock dose
Safety first
- Never mix chemicals together.
- Always add the chemical to the water — never water to the chemical.
- Wear gloves and eye protection when handling pool/spa chemicals.
- Keep chemicals out of reach of children and pets.
- Always follow the product label — it overrides any guidance here.
How it's calculated
Your shock target sits at 40% of your CYA reading. From there, it's the same chlorine math as theChlorine Calculator — just scaled to a bigger dose.
Frequently asked questions
What is "shock level" and why so much chlorine?
Shock level is roughly 40% of your CYA reading. It's a high-enough chlorine dose to rapidly kill algae and bacteria, oxidize organic waste, and break down chloramines. It's temporary — your FC will drop back to normal range within a day or two.
Why is it based on my CYA, not a fixed number?
Cyanuric acid (CYA) protects chlorine from sunlight, but it also weakens its killing power. The more CYA you have, the more FC you need for the same sanitizing effect — shock level scales with CYA for that reason.
Can I swim after shocking?
Wait until your FC drops back into the normal range (usually 24-48 hours) before swimming, or sooner if your test kit allows swimming up to a specific level — check your test kit instructions.
Which product should I shock with?
Liquid chlorine or cal-hypo (if your calcium hardness has room) are usually best — they won’t push your CYA any higher. Avoid dichlor/trichlor for shocking if your CYA is already near the top of its range.