Guide
Pool Chlorine Calculator — How Much Chlorine to Add
How a pool chlorine calculator works — raise free chlorine with liquid, cal-hypo, or trichlor using your pool volume and product strength.
A pool chlorine calculator answers one question: given your free chlorine (FC) now, your target, your pool gallons, and the strength of the product on the shelf, how much do you add?
Guessing “a jug” wastes money and can overshoot. Under-dosing leaves you chasing algae tomorrow.
What you need before you calculate
- Pool volume (gallons or litres) — from plans, or length × width × average depth × 7.5 (US gallons, rectangular).
- Current FC from a fresh test (drop kit preferred for accuracy).
- Target FC — often driven by your cyanuric acid (CYA) level, not a fixed “3 ppm for everyone.”
- Product type and strength — liquid sodium hypochlorite (%), cal-hypo (%), dichlor, trichlor, etc.
Without volume and strength, any “chlorine calculator” is theater.
Liquid chlorine vs cal-hypo vs trichlor
| Product | Typical use | Side effects |
|---|---|---|
| Liquid chlorine (bleach / pool liquid) | Raise FC fast | Raises pH slightly; no CYA |
| Cal-hypo | Raise FC; shock | Adds calcium (CH) |
| Trichlor tabs / granules | Slow FC + maintenance | Adds CYA; lowers pH |
Pick the product you actually own. Pooldex doses against your chemical strengths, not a generic default.
Worked example (liquid)
Say you need +2 ppm FC in a 15,000 gallon pool using 12.5% liquid chlorine. A proper calculator converts ppm × gallons × chemical factor into fluid ounces (or mL). Add, circulate, retest — especially before stacking another big dose.
Safety notes
- Never mix chemicals in a bucket “to save a trip.”
- Follow the label. Apps estimate; labels and local codes win.
- If you’re clearing green water, see SLAM explained — that’s a protocol, not a one-shot shock.
Log it, don’t re-guess
The second half of a chlorine calculator is the log: what you added, when, and whether FC held overnight. That’s how you learn whether your SWG, sunlight, or bather load is eating chlorine.
Pooldex is built for that loop: enter the reading → get an exact dose → save the history on your device.