Pool Chlorine Calculator
Enter your pool's gallons, the current free chlorine and cyanuric acid readings, and the product on hand. You get the dose to reach the right target for your stabilizer level, or the shock level to clear algae, in fluid ounces, gallons, ounces or pounds.
Sets how much chlorine you need. 30-50 is typical; 70-80 for salt pools.
Add liquid chlorine 12.5%
74.9 fl oz
to raise FC by 3.5 ppm
Goal
4.5 ppm FC
11.5% of CYA (TFP target for liquid/tablet chlorination), rounded
Minimum for CYA 40
3 ppm
below this, algae can take hold
Per 1 ppm in your pool
21.4 fl oz
12.5% sodium hypochlorite
Dose = 10.7 fl oz per ppm per 10,000 gal × (20,000 ÷ 10,000) × 3.5 ppm. Add with the pump running, in the evening (UV burns off free chlorine), and retest in 30 minutes. Never mix products or add water to chemical; add chemical to water.
Free chlorine targets by cyanuric acid
The FC/CYA relationship (Trouble Free Pool). Salt pools usually run CYA 60-80 and the higher targets that come with it.
| CYA (ppm) | Minimum FC | Target FC | Shock / SLAM FC |
|---|---|---|---|
| 0 | 2 | 3 | 10 |
| 20 | 2 | 3 | 10 |
| 30 | 2.5 | 3.5 | 12 |
| 40 | 3 | 4.5 | 16 |
| 50 | 4 | 6 | 20 |
| 60 | 4.5 | 7 | 24 |
| 70 | 5.5 | 8 | 28 |
| 80 | 6 | 9 | 32 |
| 90 | 7 | 10.5 | 36 |
| 100 | 7.5 | 11.5 | 40 |
Amount per 1 ppm, by product and pool size
| Product | 10K gal | 15K gal | 20K gal | 25K gal | 30K gal |
|---|---|---|---|---|---|
| Liquid chlorine 12.5% | 10.7 fl oz | 16.0 fl oz | 21.4 fl oz | 26.8 fl oz | 32.1 fl oz |
| Liquid chlorine 10% | 13.3 fl oz | 20.0 fl oz | 26.6 fl oz | 33.3 fl oz | 39.9 fl oz |
| Household bleach 6% | 21.3 fl oz | 32.0 fl oz | 42.6 fl oz | 53.3 fl oz | 63.9 fl oz |
| Cal-hypo 65% | 2.1 oz | 3.2 oz | 4.2 oz | 5.3 oz | 6.3 oz |
| Cal-hypo 73% | 1.8 oz | 2.7 oz | 3.6 oz | 4.5 oz | 5.4 oz |
| Dichlor 56% | 2.4 oz | 3.6 oz | 4.8 oz | 6.0 oz | 7.2 oz |
| Trichlor 90% | 1.5 oz | 2.3 oz | 3.0 oz | 3.8 oz | 4.5 oz |
Multiply by the ppm you want to add. Liquid products in fluid ounces (128 per gallon); granular in ounces by weight (16 per pound).
What each product leaves behind
| Product | Side effect per 10 ppm FC (10,000 gal) | Best for |
|---|---|---|
| Liquid chlorine / bleach | + about 16 ppm salt; raises pH slightly, then neutral as chlorine is used | Daily dosing, SLAM, vinyl and fibreglass pools |
| Cal-hypo | + about 7 ppm calcium hardness | Shocking plaster pools with low hardness |
| Dichlor | + about 9 ppm cyanuric acid | Fresh fills that need CYA anyway; spas |
| Trichlor tablets | + about 6 ppm CYA; lowers pH and alkalinity | Vacations and convenience; watch CYA creep |
Frequently Asked Questions
How much liquid chlorine do I add to my pool?
About 10.7 fl oz of 12.5% liquid chlorine raises 10,000 gallons by 1 ppm. To take a 20,000-gallon pool from 1 to 4 ppm: 10.7 × 2 × 3 = 64 fl oz, half a gallon. Household 6% bleach needs about twice the volume; 10% liquid chlorine about 25% more than 12.5%.
What free chlorine level should I keep?
It depends on cyanuric acid (stabilizer), which shields chlorine from the sun but also weakens it. The Trouble Free Pool guideline is a target around 7.5% of CYA and never below 5%: at CYA 30 that is 3.5 ppm (minimum 2.5); at CYA 50, 6 ppm (minimum 4); at CYA 80 for a salt pool, 9 ppm. The old "1 to 3 ppm" rule ignores CYA and is why so many stabilised pools turn green at 2 ppm.
How much shock do I need?
Shock is just a large chlorine dose. To clear algae, raise free chlorine to the SLAM level, about 40% of CYA: 12 ppm at CYA 30, 20 at CYA 50, 32 at CYA 80, and hold it there until the water clears and an overnight test loses under 1 ppm. For a 20,000-gallon pool at CYA 40 from 1 ppm, that first dose is about 2.5 gallons of 12.5% liquid or 3.9 lb of 65% cal-hypo.
Liquid chlorine, cal-hypo, dichlor or trichlor?
Liquid chlorine adds nothing but chlorine and a little salt; it is the cleanest for regular dosing. Cal-hypo adds calcium (about 7 ppm of hardness per 10 ppm of chlorine in 10,000 gallons), fine for plaster pools with low hardness, bad for pools already high. Dichlor and trichlor add cyanuric acid with every dose -- 9 ppm CYA per 10 ppm chlorine for dichlor -- which is why tablet-only pools end up at CYA 100+ and need more and more chlorine. Tablets are for convenience; use them knowingly.
When and how should I add chlorine?
In the evening, with the pump running, poured slowly in front of a return jet, never through the skimmer (it damages the pump and heater). UV destroys free chlorine, so a morning dose is half gone by afternoon. Test 30 minutes after adding, and the next morning. Never mix chemicals, and never add water to chlorine; add chlorine to water.
These calculators use published seeding rates, extension-service fertilizer guidance, and standard pool-chemistry dosing figures, and are for planning. Read the product label; it governs the dose. Pool chemicals are hazardous when mixed or mishandled, and a pool store's water test beats any estimate here.