How much chlorine for a 20,000 gallon pool?
A 20,000 gallon pool needs about 61.4 fl oz (1.9 qt) of 12.5% liquid chlorine to go from 1 ppm to 4 ppm, or 10.2 fl oz (1.3 cups) per 10,000 gal per 1 ppm.
How to work it out
- In short: work out how much chlorine the rise takes for your pool’s size, then how much of your product contains that much.
- Rise: 4 − 1 = 3 ppm
- 3 ppm × 75,708 L (20,000 gal) = 227.1 g of chlorine (1 ppm = 1 mg per litre)
- 227.1 g ÷ 125 g per litre (12.5%) = 1.817 L = 61.4 fl oz (1.9 qt)
Twenty thousand gallons is a common size for a 16 × 32 ft diving pool or an 18 × 36 sport pool. At this size liquid chlorine is bought by the case, and knowing your daily use turns a guess into a shopping list.
Adjust for your project
- Free chlorine rise
- 3 ppm
- Label-style rate
- 10.2 fl oz (1.3 cups) per 10,000 gal per 1 ppm
- Salt it leaves behind
- 4.9 ppm
- Liquid chlorine labelled 12.5% “by weight” is a little stronger per ounce than 12.5 trade percent (about 14 g of chlorine per 100 ml instead of 12.5), and every jug loses strength as it ages. Either way, retest after it circulates.
20,000 gallons, 12.5% liquid chlorine, by target level (from 1 ppm)
| Target FC | Add this much | Salt it leaves behind |
|---|---|---|
| 2 ppm | 20.5 fl oz (2.6 cups) | 1.6 ppm |
| 3 ppm | 41 fl oz (1.3 qt) | 3.3 ppm |
| 4 ppm | 61.4 fl oz (1.9 qt) | 4.9 ppm |
| 5 ppm | 81.9 fl oz (2.6 qt) | 6.6 ppm |
| 6 ppm | 102.4 fl oz (3.2 qt) | 8.2 ppm |
| 8 ppm | 1.12 gal (4.5 qt) | 11.5 ppm |
Budgeting chlorine for 20,000 gallons
Each 1 ppm of free chlorine in 20,000 gallons is about 20.5 fl oz of 12.5% liquid chlorine. Daily use depends on sun, bather load and temperature, so the useful habit is to measure it: test at the same time two evenings in a row with nothing added in between, and the drop is your daily use.
| Daily use | 12.5% liquid per day | Per week | Jugs (1 gal) per week |
|---|---|---|---|
| 2 ppm | 41 fl oz | 2.2 gal | 3 |
| 3 ppm | 61 fl oz | 3.4 gal | 4 |
| 4 ppm | 82 fl oz | 4.5 gal | 5 |
At three to five jugs a week, a salt chlorine generator starts to look attractive; the salt you would need to start one is on how much salt for a 20,000 gallon pool. If you prefer tablets, how many chlorine tablets for a 20,000 gallon pool shows the stabilizer they add.
Smaller pools: how much chlorine for a 15,000 gallon pool and how much chlorine for a 10,000 gallon pool.
Different size? Use the full Pool Chlorine Calculator.
What you’ll need
- Liquid pool chlorine (sodium hypochlorite)Budget price
Adds chlorine without stabilizer or calcium. Strength is printed on the label — commonly 10% or 12.5% — and it weakens with age and heat, so buy it fresh.
See options on Amazon (opens in a new tab) - Measuring pitcher (marked in oz and ml)Budget price
Measure doses instead of glugging from the jug. Keep one for acid and a separate one for chlorine.
See options on Amazon (opens in a new tab) - Chemical splash gogglesBudget price
Muriatic acid and liquid chlorine splash. Indirect-vent goggles cost little next to an eye injury.
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As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How much cal-hypo raises a 20,000 gallon pool by 3 ppm?
About 12.3 oz of 65% cal-hypo, adding about 2.1 ppm of calcium hardness.
How much liquid chlorine to raise a 20,000 gallon pool by 1 ppm?
About 20.5 fl oz (2.6 cups) of 12.5% liquid chlorine.
Other common sizes
- How much chlorine for a 10,000 gallon pool — 30.7 fl oz (3.8 cups)
- How much chlorine for a 15,000 gallon pool — 46.1 fl oz (1.4 qt)
Sources
- CDC Healthy Swimming — Home pool and hot tub water treatment and testing (opens in a new tab) — pH 7.0–7.8; free chlorine at least 1 ppm in pools (2 ppm with cyanuric acid) and 3 ppm in hot tubs; no CYA in hot tubs; test twice a day.
- CDC — Model Aquatic Health Code, 5th edition (2024), code (opens in a new tab) — Free chlorine minimum 1.0 ppm (2.0 with CYA, 3.0 in spas); pH 7.0–7.8; CYA at or below 90 ppm; CYA:FC above 45:1 is an imminent hazard; TA 60–180 ppm; turnover tables.
- OxyChem — Soda Bleach Solutions Handbook (re-hosted copy) (opens in a new tab) — Trade percent = grams per litre of available chlorine ÷ 10; weight % NaOCl ≈ 1.05 × weight % available chlorine; strength and specific gravity table.
- HASA — Hasachlor sodium hypochlorite SDS (2026) (opens in a new tab) — Pool liquid chlorine: sodium hypochlorite 12.5% by weight, about 1.2 g/ml.
- Hill Brothers — Sodium hypochlorite 12.5% specifications (opens in a new tab) — 12.5% by weight = 142 g/L available chlorine (14.2 trade percent), 11.9% available chlorine by weight.
- Pool Essentials chlorinating liquid (retail listing) (opens in a new tab) — A 10% sodium hypochlorite pool chlorine.
- US EPA label 57787-18 — calcium hypochlorite 65% (opens in a new tab) — 65% available chlorine; 2 oz per 10,000 gallons raises chlorine about 1 ppm; superchlorinate with 10 oz per 10,000 gallons.
- US EPA label 1258-161 — HTH calcium hypochlorite 73% (opens in a new tab) — Calcium hypochlorite 73% (70% minimum available chlorine); a 1 lb bag shock-treats 15,000 gallons.
- US EPA reg. 42177-80 — sodium dichlor label (ProPools copy) (opens in a new tab) — Dihydrate, 56% available chlorine; 2–3 oz per 10,000 gallons daily; 1 lb per 10,000 gallons to superchlorinate.
- ICC Building Safety Journal (PHTA Recreational Water Quality Committee) — Trichlor: the dependable pool performer (opens in a new tab) — Trichlor is 90% available chlorine and adds 0.6 ppm cyanuric acid for each ppm of chlorine.
- CDC — Pool chemical injuries press release (2014) (opens in a new tab) — Never mix pool chemicals, especially chlorine products with acid; add chemical to water, never water to chemical.
- CDC — Pool chemical safety: storage poster (opens in a new tab) — Separate acid and chlorine; don’t mix different types of chlorine; keep chemicals cool, dry and in original containers.
- US EPA — Introduction to pesticide labels (opens in a new tab) — Pool sanitizers are registered pesticides; the label is the law.