Pool chemical calculator
Enter your pool size, one water test, and your products. You get a numbered plan: what to add, how much, in what order, and how long to wait.
Always follow your product’s label directions. Pool and spa chlorine, bromine, shock and algaecides are EPA-registered pesticides: use products labeled for pool or spa use, and don’t swim or soak until levels are within the limit on your product’s label. If this page and a label disagree, the label wins.
On this page (10 sections)
With the default test (15,000 gallons, FC 1, pH 7.8, TA 70, CYA 40), the plan is 58 fl oz of 10% liquid chlorine (FC 1 → 4 ppm, the swim limit on many chlorine labels), then 4.2 lb of baking soda, then about 13 fl oz of 31.45% muriatic acid.
Calculator: your pool, your test, your products
The answer depends on three things you know better than any chart: pool size, product strength, and stabilizer (CYA). So the form asks for them first.
- Volume in gallons or liters. Not sure? Work it out once with the pool volume calculator, because every dose scales with it.
- Water, sanitizer, and surface. Pool or hot tub; chlorine, salt water generator (SWG), or bromine; plaster needs more calcium than vinyl, fiberglass, or an above-ground liner.
- A fresh test: free chlorine (FC), optional total chlorine (TC), pH, total alkalinity (TA), stabilizer (cyanuric acid, CYA), calcium hardness (CH), plus salt and temperature if you have them.
- Your products, with the percent printed on the label.
Everything is calculated in your browser. Nothing you type is sent anywhere. Treating a hot tub or spa instead? The hot tub chemical calculator gives doses in grams and teaspoons for 50–1,500 gallons.
Your plan: what to add first and how long to wait
Adding everything at once makes the next test meaningless and can put two reactive products in the same spot of water. The plan follows these rules:
- Chlorine first if it is below the minimum for your CYA. Sanitizing the water comes before balancing it, and the plan shows "Don't swim yet" until it is fixed.
- Alkalinity next, because TA buffers pH. Taylor's instructions say to bring TA into range before adjusting pH.
- pH third. Baking soda nudges pH up a little, so the plan asks you to retest pH before the acid step.
- Calcium, stabilizer, and salt last. They dissolve slowly and don't affect how well the water is sanitized today.
Between products, keep the pump running and wait 30 minutes (our default, not a standard). The full reasoning is in the order to add pool chemicals.
Large corrections are split on purpose. The calculator never lowers pH by more than 0.4 or TA by more than 20 ppm in one acid step, never raises TA by more than 30 ppm with one baking soda dose, and never raises calcium by more than 50 ppm at a time. When a correction is bigger, you see "Add in N steps" with a retest between them. One 2026 App Store review of a brand-name pool app complained it said to "add an entire bag of Ph Up chemical." Step limits are there to prevent that.
Target ranges we use and why (CDC, PHTA, Taylor)
| Reading | We aim for | Acceptable | Where it comes from |
|---|---|---|---|
| Free chlorine (FC) | depends on CYA: 3–5 ppm at CYA 40 | at least 1 ppm without CYA, 2 ppm with CYA; never above 10 | CDC minimums; MAHC 2024 Annex for the CYA link and the 10 ppm limit |
| pH | 7.4–7.6 | 7.2–7.8 | CDC lists 7.0–7.8 for home pools; PHTA and Taylor 7.2–7.8 |
| Total alkalinity (TA) | 80–120 ppm | 60–180 ppm | Taylor ideal range; APSP range as published by PHTA |
| Calcium hardness (CH) | plaster 200–400; vinyl, fiberglass, above-ground 150–250 | 150–1,000 ppm | Taylor ideal; APSP range; the split by surface is our choice |
| Stabilizer (CYA) | 30–50 ppm (salt pools 60–80) | up to 100 ppm | Taylor and APSP; Hayward allows up to 80 ppm for its salt cells |
| Salt (SWG only) | 3,200 ppm | 2,700–3,400 ppm | Hayward AquaRite manual; check your own cell's manual |
Why aim for pH 7.4–7.6 and not anywhere in 7.2–7.8? The MAHC Annex explains that the active, germ-killing part of chlorine (hypochlorous acid) is about 70% of free chlorine at pH 7.0, about 50% at 7.5, and only about 20% at 8.0. Keeping pH near 7.5 means the chlorine you paid for does its job. The full chart with hot tub ranges is on the pool chemistry chart.
Why the right chlorine level depends on stabilizer (CYA)
Stabilizer shields chlorine from sunlight, but it also holds most of that chlorine in reserve. The more CYA you have, the more free chlorine you need for the same disinfecting power. That is why this calculator asks for CYA before it sets a chlorine target. At CYA 30, the minimum is 2.5 ppm; at CYA 40, it is 3 ppm; at CYA 80, it climbs to 6 ppm. That is already above the 4 ppm most pool product labels allow for swimming. Keeping CYA at 30–50 ppm is the simplest way to stay inside both limits. The table for every CYA level is on what your chlorine level should be.
Product strength matters: 6% bleach vs 12.5% liquid chlorine
For a 15,000-gallon pool, raising FC by 1 ppm takes about 15 fl oz of 12.5% pool chlorine, 19 fl oz of 10% pool chlorine, or 31 fl oz of 6% household bleach. Same job, twice the volume. Two things cause the gap:
- Different label math. Pool chlorine is sold in "trade percent" (grams of available chlorine per liter ÷ 10), while bleach is labeled in percent sodium hypochlorite by weight. By our conversion, 6% bleach carries about 62 g of available chlorine per liter, roughly half of the 125 g in 12.5% pool chlorine.
- Age and heat. PHTA data show 12.5% sodium hypochlorite loses half its strength in about 180 days at 77 °F and in about 48 days at 95 °F. An old jug from a hot garage can be much weaker than its label.
Pick the exact product and percent in the form. If a retest shows less chlorine than predicted, the liquid chlorine calculator lets you enter how much strength your jug has left.
Safety: never mix chemicals, add chemicals to water
Before you add anything:
- Never mix pool chemicals with each other, even in a bucket or a skimmer. Chlorine and acid together release chlorine gas.
- Add chemicals to water, never water to chemicals. Pre-dissolve granules in a clean bucket of pool water when the label says to.
- Wear gloves and eye protection. Pour slowly, close to the water, with the pump running.
- Store chlorine and acid apart, in a cool, shaded, ventilated place, out of reach of children.
- Always follow the product label. It is a violation of federal law to use a pesticide product in a manner inconsistent with its labeling.
- If someone swallows a pool chemical or gets it in their eyes, call Poison Control at 1-800-222-1222 (US).
This is not a remote risk: the CDC counted about 4,535 emergency department visits a year linked to pool chemicals in 2008–2017. Storage, first aid, and what to do after a spill are covered in the pool chemical safety guide.
How this calculator was checked (Taylor K-1005 and EPA label examples)
The same formulas run on every page of this site and will run in our iPhone app. They must pass 67 reference cases before any release. A few checks against published values:
- 10,000 gal, +1 ppm FC with 10% liquid chlorine: 12.80 fl oz (Taylor K-1005 table: 12.8 fl oz).
- 10,000 gal, +1 ppm FC with 65% calcium hypochlorite (cal-hypo): 2.054 oz (Taylor: 2.05 oz).
- 10,000 gal, +10 ppm TA with baking soda: 1.401 lb (Taylor: 1.40 lb).
- One quart of 5.25% bleach in 6,000 gallons: +2.24 ppm (an older EPA-registered bleach label says about 2 ppm).
The pH step uses a carbonate chemistry model, not a fixed "ounces per 0.1 pH" rule. Every constant, formula, and known limitation is on the methodology page.
Is there a pool chemical calculator app?
Yes, several, and Pooldex is building one for iPhone, based on the same formulas as this page. The website calculator works now, in any browser, with no account. The app adds what a web page can't: it keeps your pool and products saved, logs every test, and reminds you when to retest after each step. Details are on the Pooldex app page. For a neutral look at the apps you can download today, see pool chemistry apps compared.
FAQ
How to know how much pool chemicals to use?
You need three numbers: your pool volume, a current test, and the strength of the product you own. The math is the same for every product: grams of active ingredient = ppm change × liters ÷ 1,000, then divided by the product's strength. The calculator above does that for all your readings at once and puts the steps in the recommended order.
How much chlorine do I put in my pool calculator?
Start from how many ppm you need (target FC minus current FC). Each ppm in 10,000 gallons takes 12.8 fl oz of 10% liquid chlorine or 10.24 fl oz of 12.5%. Multiply by the ppm and by your volume in 10,000s. The chlorine dose calculator does this for bleach, tablets, and powders too.
Sources
- CDC, Home pool and hot tub water treatment and testing: cdc.gov
- CDC, Model Aquatic Health Code 2024, Annex (5.7.3.1.1.2 and the pH/HOCl discussion): cdc.gov (PDF)
- CDC, Pool chemical injuries 2008–2017: archive.cdc.gov
- Taylor Technologies, K-1005 instructions and treatment tables: PDF
- PHTA fact sheet, Sodium hypochlorite: phta.org
- Hayward, AquaRite manual (salt range): PDF
- Poison Control (US): poison.org