Pool Chlorine Calculator: How Much Chlorine to Add

Chlorine is your pool's sanitizer, and adding the right amount — enough to reach the 1–3 ppm free-chlorine range without wildly overshooting — depends on your pool volume and how far you need to raise it. The calculator above does that math; here's how to use it well.

What the calculator needs

Enter your pool volume in gallons and your current and target free chlorine, and the tool estimates how much of your chlorine product to add. Different chlorine sources — liquid chlorine, cal-hypo, dichlor, trichlor tablets — have different strengths, so match the calculator's product type to what you're actually using. Volume is the critical input, so have an accurate gallon figure (our volume calculator handles that) before dosing.

Read the label alongside it

Treat the calculator as a starting point and the product label as the authority. Product concentrations vary by brand, so confirm the dose against the label for your specific chlorine, and note that stabilized products (dichlor, trichlor) also add cyanuric acid over time, which matters for long-term balance. Add with the pump running so it circulates, and give it time before you judge the result.

Add, circulate, retest

Sneak up on the target rather than dumping a big dose. Add the calculated amount, let it circulate, and retest before adding more — it's easier to add a little more chlorine than to bring an overshoot back down. If your chlorine never seems to hold no matter how much you add, the issue is usually low stabilizer (sunlight burning it off) or high stabilizer (locking it up), not the dose — check CYA before chasing the chlorine number.