Pool Chlorine Calculator
Enter your pool size and current reading to see how much chlorine to add to reach your target free chlorine level.
| Current ppm | To reach 3 ppm (oz liquid) |
|---|---|
| 0 | 57.6 oz |
| 0.5 | 48.0 oz |
| 1 | 38.4 oz |
Test free chlorine first
Free chlorine is the active sanitizer, and it is the number that matters for dosing. Combined chlorine, the used-up form, does not sanitize and can be burned off with shock instead. Test with a drop kit for a real number, then subtract your current reading from your target to find the raise you need.
Liquid versus granular versus tablets
Liquid chlorine at 12.5 percent is the fastest way to lift free chlorine and adds no stabilizer. Granular chlorine is stronger by weight, so it takes fewer ounces, but it dissolves best when you pre-mix it. Tablets dissolve slowly and are built for steady background sanitizing, so they cannot fix a low reading in an afternoon.
Add chlorine safely and retest
Pour liquid chlorine near the deep end or in front of a return with the pump running, and never mix it with acid or other chemicals. Wait about 30 minutes, then retest free chlorine before adding more. Keep total chlorine under about 5 ppm for comfortable swimming, and run the pump after dosing so the chlorine spreads.
Our picks
Questions about this calculator
How much chlorine do I add to my pool?
Dose by pool volume and the raise you need. Liquid 12.5 percent adds about 12.8 ounces per 10,000 gallons for each 1 ppm. A 15,000 gallon pool that needs to go from 1 ppm to 3 ppm takes about 38 ounces, or just under 5 cups.
How much does a gallon of liquid chlorine raise chlorine?
One gallon, or 128 ounces, of 12.5 percent liquid chlorine raises a 10,000 gallon pool by about 10 ppm. In a 20,000 gallon pool the same gallon adds about 5 ppm. Strength drops as the jug ages, so test after you pour.
How many ppm should free chlorine be?
Most backyard pools run best between 2 and 3 ppm free chlorine. A covered or lightly used pool can sit near 2 ppm, and a busy pool in hot weather does better near 3 ppm. Never let it fall to zero.
Can I use tablets to raise chlorine fast?
No. Trichlor tablets dissolve over several days, which is fine for steady background sanitizing but far too slow to fix a low reading today. Use liquid or pre-dissolved granular chlorine when you need free chlorine to come up quickly.
How long after adding chlorine can I swim?
Wait until free chlorine reads at or below about 5 ppm, and pH is between 7.2 and 7.8. After a normal dose that is often 30 to 60 minutes with the pump running. After a heavy shock, wait longer and retest before anyone gets in.
Should I add chlorine at night?
Evening is a good time because sunlight burns off unstabilized chlorine. Adding after the sun is low lets more of the dose do its job. Run the pump after dosing so the chlorine mixes through the whole pool.
What if my chlorine is already at target?
Then no dose is needed. The calculator says none needed and tells you not to raise it further. Check pH and cyanuric acid instead, since chlorine works poorly when pH is off or stabilizer is far too high.