How to use the pool chlorine calculator
- Enter the pool volume in gallons. The pool volume calculator works it out from the pool’s size.
- Test the water and enter the free chlorine reading, then the level you want.
- Pick your product and check the strength against the label. The calculator starts with the usual strength for each type.
Add chlorine with the pump running, then retest after a few hours.
The formula
- Chlorine needed (lb) = gallons × 8.34 × (target − current ppm) ÷ 1,000,000
- Granules or tablets (lb) = chlorine needed ÷ strength
- Liquids (mL) = chlorine needed in grams ÷ strength, with the strength read as grams per 100 mL
Worked example: 20,000 gallons, 1 to 3 ppm
- Chlorine needed: 20,000 × 8.34 × 2 ÷ 1,000,000 = 0.334 lb (151 g)
- 10% liquid chlorine: 151 ÷ 0.10 = 1,513 mL = 51 fl oz
- 65% cal-hypo instead: 0.334 ÷ 0.65 = 0.51 lb = 8.2 oz
Dose to raise 1 ppm in 10,000 gallons
| Product | Strength | Amount |
|---|---|---|
| Liquid chlorine | 12.5% | 10.2 fl oz |
| Liquid chlorine | 10% | 12.8 fl oz |
| Household bleach | 6% | 21.3 fl oz |
| Cal-hypo | 65% | 2.1 oz |
| Dichlor | 56% | 2.4 oz |
| Trichlor | 90% | 1.5 oz |
Frequently asked questions
How much liquid chlorine raises 1 ppm in 10,000 gallons?
About 10 fl oz of 12.5% liquid chlorine, 13 fl oz of 10%, or 21 fl oz of 6% household bleach. Double it for 20,000 gallons or for a 2 ppm rise.
How much cal-hypo shock does a 20,000 gallon pool need?
To go from 1 to 10 ppm, about 2.31 lb of 65% calcium hypochlorite, or 1.8 gallons of 10% liquid chlorine. The right shock level depends on your stabilizer (cyanuric acid) reading, so follow the product label or your test kit's guide for the target.
What should the chlorine level be in a pool?
The CDC recommends at least 1 ppm of free chlorine in pools, at least 2 ppm if you use stabilized chlorine (dichlor or trichlor) or add cyanuric acid, and at least 3 ppm in hot tubs, with the pH between 7.0 and 7.8.
Can I use household bleach in my pool?
Plain, unscented bleach is the same chemical as pool liquid chlorine, only weaker. For a 20,000 gallon pool, raising free chlorine by 2 ppm takes about 85 fl oz of 6% bleach. Skip scented or splash-less versions, which contain additives.
What's the difference between dichlor and trichlor?
Both are stabilized chlorine that adds cyanuric acid to the water along with the chlorine. Dichlor granules dissolve quickly and suit topping up; trichlor tablets dissolve slowly in a floater, skimmer or feeder for day-to-day chlorine, so they aren't the way to raise the level fast.
Why use free chlorine and not total chlorine?
Free chlorine is the part still able to kill germs. Total chlorine also counts chlorine already tied up (combined chlorine), so test free chlorine with a DPD or FAS-DPD kit and enter that reading.
Sources
Formulas and defaults last reviewed October 30, 2026. How we check our math.