Free pool tool
Pool Chlorine Calculator
Enter your pool volume, your free chlorine reading and the level you want to reach, and the calculator works out how much of each common chlorine product to add. It also shows what else each product puts into the water.
Not sure? Work out your pool volume.
Most pools hold 3 to 5 ppm. With more stabilizer you need more chlorine.
Add Liquid chlorine (12.5%)
38 fl oz
The same dose in other products
| Liquid chlorine (12.5%) | 38 fl oz |
| Liquid chlorine (10%) | 48 fl oz |
| Unscented bleach (8.25%) | 58 fl oz |
| Unscented bleach (6%) | 80 fl oz |
| Cal-hypo (65%) | 7.7 oz |
| Cal-hypo (73%) | 6.9 oz |
| Dichlor (56%) | 8.9 oz |
| Trichlor (90%) | 5.6 oz |
- Adds nothing but chlorine and a little salt. It loses strength in the heat, so a jug that has sat in the sun may be weaker than its label.
- Add about three quarters of the dose, let the pump circulate for an hour, and re-test before adding the rest. Never mix chemicals together, and always add chemicals to water rather than water to chemicals.
How it works
A Chlorine Dose Is the Rise in ppm Times the Water
One part per million in water is one milligram per litre. Raising free chlorine by 3 ppm in a pool therefore takes 3 milligrams of available chlorine for every litre of water, and the only other question is how strong the product is.
Liquid product (mL) = mg needed ÷ (strength % × 10)
Dry product (g) = mg needed ÷ 1,000 ÷ (strength % ÷ 100)
Liquid chlorine and bleach are labelled by strength as a percentage, and the calculator uses that number the way most pool dosing charts do. Liquid chlorine weakens as it sits, especially in the heat, so a jug that has spent the summer on a truck may be noticeably weaker than its label. If your doses consistently fall short, that is the first thing to suspect.
Worked example
15,000 Gallons, Raising Free Chlorine by 3 ppm
A 15,000-gallon pool holds about 56,800 litres. Raising free chlorine by 3 ppm needs 3 × 56,800, or about 170,300 milligrams of available chlorine. Liquid chlorine at 12.5% carries 125 milligrams per millilitre, so the pool needs about 1,360 mL, which is 46 fl oz, or a little over a third of a gallon.
170,344 mg ÷ 125 mg/mL ≈ 1,363 mL ≈ 46 fl oz of 12.5% liquid chlorine
The same rise takes 58 fl oz of 10% liquid chlorine, 70 fl oz of 8.25% bleach, 9.2 oz of 65% cal-hypo or 11 oz of dichlor. Add most of the dose, let the pump circulate it, and re-test before adding the rest.
Choosing a product
What Each Kind of Chlorine Leaves Behind
Every chlorine product adds chlorine, but the solid ones also add something that stays in the pool long after the chlorine is gone. The amounts below come from the molecular weights of each compound, so they hold for any pool size.
Dichlor: +0.91 ppm cyanuric acid per 1 ppm of chlorine
Trichlor: +0.61 ppm cyanuric acid per 1 ppm of chlorine
Those side effects add up. A pool fed only with trichlor tablets gains stabilizer every week until the chlorine struggles to work, and a plaster pool dosed with cal-hypo in an area with hard fill water can drift toward scaling. Liquid chlorine adds nothing but chlorine and a little salt, which makes it the easiest product to plan around. The calculator lists what each option adds, so you can see the trade-off before you choose.
Setting a target
The Right Chlorine Level Depends on Your Stabilizer
Cyanuric acid protects chlorine from sunlight by holding most of it in reserve, which means the more stabilizer a pool has, the more free chlorine it needs to stay sanitized. A widely used rule is to keep free chlorine at no less than about 7.5% of the cyanuric acid level. A pool at 30 ppm of stabilizer needs at least about 2 ppm, and a salt pool at 70 ppm needs at least about 5.
If you are clearing algae or a green pool, you need a much higher level held for longer, which the pool shock calculator works out from your stabilizer reading. For more on routine dosing, the guide to how much chlorine to add to a pool covers testing, timing and the readings that matter alongside chlorine. Never mix two chlorine products together, and always add chlorine to the pool rather than water to the chemical.
For pool service companies
The same maths runs at every stop in Pool Runs
These calculators use the dosing and saturation-index formulas built into the Pool Runs technician app. A tech logs the readings at the pool, the app works out the doses for that pool's own volume, and the visit lands in the customer's service history and report without anyone typing it up later.
- Readings and doses saved against each pool, with the saturation index for every visit
- A mobile app that works offline in a backyard with no signal
- Chemicals and parts tracked on every truck and in the shop
Try Pool Runs free
Free for 30 days, month to month, with white-glove onboarding to move your customers in.
Questions
Pool Chlorine Calculator FAQ
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