Pool Chlorine Calculator
Liquid chlorine (fl oz) = gallons × ppm rise × 128 ÷ 1,000,000 ÷ strength. Raising 15,000 gallons from 1 to 3 ppm takes 30.7 fl oz of 12.5 % chlorine. Your product label gives a dose for its own strength: pick « Use the dose printed on my label » and the tool scales it.
Liquid chlorine 12.5 % to add
Follow the product label: its dose comes first. Add with nobody in the pool.
30.7 fl oz
+2 ppm in 15,000 gal
- In gallons
- 0.24 gal (0.96 qt)
- +1 ppm in 10,000 gal
- 10.24 fl oz
Indiana Dept. of Health: add a large dose in thirds over 2 hours, when the pool is not in use.
Worked examples
15,000 gal from 1 to 3 ppm with 12.5 % liquid chlorine
- ppm rise = 3 − 1 = 2 ppm
- 15,000 × 128 × 2 ÷ 1,000,000 = 3.84 fl oz of pure chlorine
- 3.84 ÷ 0.125 = 30.72, so 30.7 fl oz (0.24 gal)
Result: 30.7 fl oz of 12.5 % liquid chlorine.
Checked by the automated test “pool chlorine — defaults: 15,000 gal from 1 to 3 ppm with 12.5 % liquid chlorine → 30.7 fl oz”.
Indiana's label example: 60,000 gal from 1 to 10 ppm
- The label: 20 oz of cal-hypo raises 10 ppm in 10,000 gal
- 20 × (60,000 ÷ 10,000) × (9 ÷ 10) = 108 oz
- 108 ÷ 16 = 6.75 lb
Result: 108 oz (6.75 lb) of calcium hypochlorite.
Checked by the automated test “pool chlorine — label mode: the Indiana label (20 oz for +10 ppm in 10,000 gal), 60,000 gal from 1 to 10 → 108 oz”.
How it works
ppm rise = chlorine wanted − chlorine now
With a label: amount = label amount × (pool gallons ÷ label gallons) × (ppm rise ÷ label ppm)
Without a label, 1 ppm in 10,000 gal = 10,000 × 8.345 lb × 10⁻⁶ = 1.335 oz of available chlorine
Dry product (oz) = gallons × 8.345 × 16 × ppm rise ÷ 1,000,000 ÷ strength · Liquid (fl oz) = gallons × 128 × ppm rise ÷ 1,000,000 ÷ strength
Assumptions
- Formulas of the Indiana Department of Health. Strength = percent available chlorine on the label: 10 or 12.5 % liquid chlorine (sodium hypochlorite), 65 or 73 % cal-hypo, 56 % dichlor, 90 % trichlor.
- Liquid strength is read per volume, as in the Indiana table: 12 % liquid takes 10.7 fl oz for +1 ppm in 10,000 gal. Dry products are weighed: 2 oz of 67 % cal-hypo for the same rise.
- The dose raises free chlorine in clean water. Water with algae or a heavy load uses chlorine up as you add it: test again and repeat. Lowering chlorine is not a dose: the tool returns 0.
Reference table
| Product | +1 ppm | +10 ppm |
|---|---|---|
| Liquid chlorine 10 % | 12.8 fl oz | 1 gal |
| Liquid chlorine 12.5 % | 10.2 fl oz | 0.8 gal |
| Cal-hypo 65 % | 2.1 oz | 1.28 lb |
| Cal-hypo 73 % | 1.8 oz | 1.14 lb |
| Dichlor 56 % | 2.4 oz | 1.49 lb |
| Trichlor 90 % | 1.5 oz | 14.8 oz |
Liquids in fluid ounces or gallons, dry products by weight. For 20,000 gal double the figures, for 5,000 gal halve them.
Before you pour
- Test first. Enter the free chlorine your test kit reads today, not the level you think the pool holds.
- Know the gallons. Every dose is proportional to the water volume: the pool volume calculator gives it from the shape and depths.
- Read the strength. The percent of available chlorine is on the label; an unknown product is entered with « Other ».
Common mistakes
- Mixing cal-hypo and trichlor Oreq's trichlor tablet safety data sheet lists calcium hypochlorite as incompatible and bans feeders holding remnants of another product: fire or explosion. HTH's cal-hypo sheet warns the same. Never share a feeder or a scoop between them.
- Guessing the pool volume The dose is proportional to the gallons: a pool taken for 15,000 gal that holds 20,000 gets three quarters of the dose. Measure it once with the pool volume calculator.
- Ignoring the stabilizer Dichlor and trichlor add cyanuric acid with every dose. CDC asks for at least 2 ppm free chlorine with them, against 1 ppm without, and recommends against them in hot tubs.
- Testing a shocked pool too soon Over 10 ppm, CDC warns that a test can bleach out and read low or 0. A low reading right after a shock does not mean you should add more.
- Adjusting with the pH off Indiana asks for pH 7.2 to 7.8 before you add chlorine: chlorine compounds move the pH and work less well outside that range.
Frequently asked questions
How much chlorine do I add to my pool?
For liquid chlorine, fl oz = gallons × ppm rise × 128 ÷ 1,000,000 ÷ strength. 15,000 gal from 1 to 3 ppm takes 30.7 fl oz of 12.5 % chlorine, or 6.2 oz of 65 % cal-hypo. CDC asks for at least 1 ppm.
How much liquid chlorine do I add to a pool?
10.2 fl oz of 12.5 % liquid chlorine raises 10,000 gal by 1 ppm (12.8 fl oz at 10 %). Scale it to your gallons and your ppm rise: 20,000 gal from 1 to 4 ppm takes 61.4 fl oz, about half a gallon.
How much shock do I add to my pool?
What the shock's label says, scaled to your pool. With the Indiana example label, 20 oz of cal-hypo per 10 ppm in 10,000 gal, 15,000 gal from 1 to 10 ppm takes 27 oz. Without a label, 65 % cal-hypo takes 27.7 oz.
How many gallons of liquid chlorine to shock a pool?
Raising 15,000 gal from 1 to 10 ppm takes 138 fl oz of 12.5 % liquid chlorine, 1.08 gal; at 10 %, 1.35 gal. Indiana adds a large dose in thirds over 2 hours.
Sources
Formula, examples and sources checked on by the Yardstick Math team. How we check our formulas.
- Adjusting Chemical Levels in a Swimming Pool (label formulas, 1 ppm = 0.083 lb per 10,000 gal, adjustment table) — Indiana Department of Health, accessed
- Home Pool and Hot Tub Water Treatment and Testing (at least 1 ppm, 2 ppm with cyanuric acid; tests bleach over 10 ppm) — CDC, accessed
- HTH Pool Care Shock Advanced, Safety Data Sheet (calcium hypochlorite; other pool treatment products incompatible) — Innovative Water Care (HTH), accessed
- ClearView 3 in Jumbo Tabs (trichlor), Safety Data Sheet (calcium hypochlorite incompatible; no feeder with remnants of another product) — Oreq Corporation, accessed