Pool Chemical Calculator

Pool chemical calculator for chlorine, pH, alkalinity and stabilizer: enter your test readings and pool volume to get the dose of each product in ounces and grams, with shock folded in.

Quick answer

Pool chemical doses come from one identity: 1 ppm is 1 mg per litre, divided by how much of the product is actually active. Enter your pool volume in gallons or litres, pick the job — chlorine, shock, alkalinity, pH up, pH down, stabilizer — and this calculator returns the dose in US units and metric together. pH is the exception and the reason a single calculator beats six: the acid or soda ash a pH move needs depends on your alkalinity and stabilizer readings, so those are asked for rather than assumed.

Your pool and your test kit

Pool volume

≈ 37,854 L. Accepts 26–1,320,860 gal. Not sure? Work it out from your pool’s shape.

Units

What needs fixing?

Free chlorine now (ppm)

Target free chlorine

Aim for 10–15% of your stabilizer reading — the full table by CYA level.

Chlorine product

Add Liquid chlorine 12.5%

20 fl oz

US units

606 ml

Metric

Takes free chlorine from 1 to 3 ppm.

Before you pour anything

Never mix pool chemicals with each other — not in a bucket, not in a scoop, not in the skimmer. Cal-hypo and trichlor together can catch fire.
Always add chemicals to water, never water to chemicals, and never water to acid.
Run the pump while you dose and for several hours afterwards.
One chemical at a time. Retest before the next one — the last dose has probably moved it.

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Why One Calculator Instead of Six

Most pool sites give you a separate page per chemical, and the split quietly hides the thing that matters: the doses interact. Every scoop of stabilized chlorine leaves cyanuric acid behind — dichlor adds 9.1 ppm of it for every 10 ppm of chlorine it delivers — and cyanuric acid raises the chlorine level your pool needs from then on. A puck feeder holding free chlorine up by 2 ppm a day adds roughly 37 ppm of stabilizer over a 30-day month, which is how a pool that was fine in June is fighting algae in August with the same routine. Cal-hypo has its own passenger: 7.1 ppm of calcium hardness per 10 ppm of chlorine, which is nothing in soft water and scale on the tiles in hard water.

The same tangle runs through the rest of it. Baking soda raises alkalinity and nudges pH up with it. Acid lowers pH and takes alkalinity down too. Soda ash raises both. A tool that treats them as six independent problems will happily send you round in circles, so this one keeps them in one place and names the side effect on the same screen as the dose.

What This Pool Chemical Dosage Calculator Computes

Chlorine, alkalinity and stabilizer are linear: 1 ppm is 1 mg per litre, so the mass of active agent is the change you want multiplied by the volume, divided by the product’s active fraction. That is why strength matters more than brand — 12.5% liquid and 10% liquid differ by a quarter, and 73% cal-hypo does the same work as 65% in 11% less weight.

pH does not work that way, and this is where a swimming pool chemical calculator either earns its keep or misleads you. Pool water is buffered, so the acid a pH move takes depends on how much buffer is in the water — alkalinity, and stabilizer, which buffers too. This page solves the carbonate and cyanurate equilibrium at your readings rather than reading a fixed ounces-per-0.1-pH table, and the difference is not small: at the two ends of a normal alkalinity range the same pH move needs 1.9 times as much acid.

The Honest Limits

The pH figures are estimates and are presented that way. The model assumes 25°C water, no borates, and ignores salt and ionic strength; muriatic acid is computed as the 31.45% (20°Bé) US bottle, so a different concentration needs scaling by the ratio of strengths. Real pools bring measurement error of their own — a drop test resolves alkalinity to about 10 ppm, and every dose here is only as good as the reading you fed it. Treat the result as a first dose, add it with the pump running, wait four hours, and retest. The chlorine, alkalinity and stabilizer numbers are on firmer ground: those are stoichiometry, computed from the available-chlorine percentage each product states on its own label. Where a label’s dosing chart disagrees with what you read here, follow the label — brands round their charts to whole scoops and cups, and they round conservatively, so their figures differ from each other as much as they differ from ours.

The chemistry behind the page is standard and checkable. Product strengths are the figures on mainstream US and EU labels; alkalinity uses the 84/50 equivalent-weight ratio for sodium bicarbonate; the carbonate equilibrium constants are the 25°C freshwater values from Stumm and Morgan; the chlorine and stabilizer relationship comes from the hypochlorous-acid and cyanurate binding work of O’Brien, Morris and Butler (1974), which is what the familiar FC/CYA chart is built on.

Litres and Grams, Not Converted Gallons

Nearly every pool dosing chart online is written for a 10,000-gallon US pool, and metric owners are left dividing by 3.785. This one is metric-native: type litres, get grams, kilograms and millilitres, and read reference tables built on round metric pool sizes rather than the awkward conversions of American ones. Both systems appear on every result, because plenty of people buy a US-labelled product for a pool they measured in metres.

Working through a whole set of readings? The pool volume calculator works out the number every dose on this page depends on, and hands it straight to this one — unless you have already typed a volume in here, in which case yours stays put. The cyanuric acid calculator goes deeper on stabilizer, including the only way to bring it down, and the pool salt calculator covers salt-water generators.

Chlorine dose to raise free chlorine by 4 ppm (US pool sizes)

Product	5,000 gal	10,000 gal	15,000 gal	20,000 gal	25,000 gal
Liquid chlorine 10%	26 fl oz	51 fl oz (0.4 gal)	77 fl oz (0.6 gal)	102 fl oz (0.8 gal)	1 gal
Liquid chlorine 12.5%	20 fl oz	41 fl oz (0.32 gal)	61 fl oz (0.48 gal)	82 fl oz (0.64 gal)	102 fl oz (0.8 gal)
Cal-hypo granules 65%	4 oz	8 oz	12 oz	1 lb	1.3 lb
Cal-hypo granules 73%	3.7 oz	7 oz	11 oz	15 oz	1.1 lb
Dichlor granules 55.5%	5 oz	10 oz	14 oz	1.2 lb	1.5 lb
Trichlor tablets 90%	3 oz	6 oz	9 oz	12 oz	15 oz

Liquid products are dosed by volume, granules and tablets by weight. Dichlor and trichlor also add cyanuric acid, and cal-hypo adds calcium hardness — neither leaves the water again except by dilution. Computed from the same functions the calculator above runs.

Chlorine dose to raise free chlorine by 4 ppm (metric pool sizes)

Product	20,000 L	40,000 L	60,000 L	80,000 L	100,000 L
Liquid chlorine 10%	800 ml	1.6 L	2.4 L	3.2 L	4 L
Liquid chlorine 12.5%	640 ml	1.28 L	1.92 L	2.56 L	3.2 L
Cal-hypo granules 65%	123 g	246 g	369 g	492 g	615 g
Cal-hypo granules 73%	110 g	219 g	329 g	438 g	548 g
Dichlor granules 55.5%	144 g	288 g	432 g	577 g	721 g
Trichlor tablets 90%	89 g	178 g	267 g	356 g	444 g

Round metric pool sizes, not converted gallons. Same chemistry as the table above, expressed in grams and millilitres.

Baking soda to raise total alkalinity by 10 ppm

Pool size	Sodium bicarbonate
5,000 gal (18,927 L)	11 oz (318 g)
20,000 L (5,283 gal)	12 oz (336 g)
10,000 gal (37,854 L)	1.4 lb (636 g)
40,000 L (10,567 gal)	1.5 lb (672 g)
15,000 gal (56,781 L)	2.1 lb (954 g)
60,000 L (15,850 gal)	2.2 lb (1.01 kg)
20,000 gal (75,708 L)	2.8 lb (1.27 kg)
80,000 L (21,134 gal)	3 lb (1.34 kg)
25,000 gal (94,635 L)	3.5 lb (1.59 kg)
100,000 L (26,417 gal)	3.7 lb (1.68 kg)

Scales linearly: double the lift, double the dose. The usual target band is 60–120 ppm. Expect pH to drift up with alkalinity, so retest it afterwards.

Muriatic acid for the SAME pH move, by alkalinity

Total alkalinity	Muriatic acid 31.45%
60 ppm	7.4 fl oz (218 ml)
80 ppm	9 fl oz (269 ml)
100 ppm	11 fl oz (320 ml)
120 ppm	13 fl oz (371 ml)
140 ppm	14 fl oz (422 ml)

Taking pH from 7.8 to 7.5 in a 10,000 gallon pool at 40 ppm cyanuric acid, 25°C, no borates. This is the table nobody publishes: the pH move is identical in every row and the dose spans 1.9×, because alkalinity is what resists the change. A fixed ounces-per-0.1-pH rule is wrong at both ends of this column.

Shock Is a Chlorine Level, Not a Product

“Shock” on a bag means a strong dose of chlorine, and nothing more. What separates a routine shock from clearing a green pool is the level you take the water to and how long you hold it there. Routine maintenance is a flat 10 ppm of free chlorine, once, to burn off combined chlorine — the same level for every pool, which is why the calculator does not ask for your stabilizer reading in that scenario. Algae is the one that moves with the water: hold free chlorine at 40% of your stabilizer reading above roughly 25 ppm, and at a floor of 10 ppm below that, where the published chart stops scaling because a fraction of a small number is less chlorine than any pool needs to clear algae. Whichever of those two governs your target, you hold it there several times a day, for days, brushing and filtering the whole time, until it stops falling overnight. That target the calculator does compute from your own cyanuric acid number rather than from a scoop size, because a pool at 30 ppm and a pool at 80 ppm need very different amounts of the same product to do the same job.

The flat number has a ceiling worth knowing. From 70 ppm of stabilizer upwards, the everyday band a pool should already be sitting in has reached 10 ppm, so a “routine shock” at that reading no longer lifts the water above where it belongs anyway — and further up the scale it does not even reach the band. At that point the useful moves are the algae protocol or bringing the stabilizer down, not a bigger bag.

One warning worth repeating: if free chlorine will not hold overnight, no single dose fixes it. Something in the pool is eating chlorine — algae in the filter, a dead spot with no circulation, phosphate-fed growth, or organic load nobody has brushed loose. Adding a bigger dose to the same problem is how people spend a fortnight and a month of stabilizer getting nowhere. Stabilizer, in particular, only ever goes up: keep it in the 30–50 ppm band for an outdoor pool and reach for unstabilized chlorine once you are there.

How to work out a pool chemical dose

Five steps, computed in your browser from your own test readings.

Put in your pool volume
Type the volume and pick gallons or litres — the whole page works natively in both, so a 40,000 L pool gets 960 ml of 12.5% liquid chlorine for a 3 ppm lift without anyone converting anything. If you came from the pool volume calculator, the number is already filled in.
Pick the job
Six jobs share one calculator: raise chlorine, shock, raise alkalinity, lower pH, raise pH, and raise stabilizer. Picking one changes which test-kit readings it asks for, because that is what changes the dose.
Enter what your test kit says, not what you hope
Current and target for the reading you are moving, plus alkalinity and stabilizer for the pH jobs, because a buffered pool resists a pH move in proportion to both. Guessed inputs give confident wrong answers; a drop test costs a minute.
Read the dose in both unit systems
The result gives US units and metric side by side — 672 g of baking soda for a 10 ppm alkalinity lift in 40,000 L, and the pounds-and-ounces equivalent beside it. When a product carries a passenger, the panel says so: stabilized chlorine adds cyanuric acid, cal-hypo adds calcium.
Dose one thing, then retest
Add the chemical with the pump running, never mixing products, and wait before touching anything else — four hours for acid, a full turnover for granules, a week for stabilizer. Then retest and come back. Most pool problems are one chemical dosed twice because nobody waited for the first one.

Frequently Asked Questions

How much liquid chlorine do I add to a 10,000 gallon pool?

To raise free chlorine by 2 ppm in 10,000 gal (37,854 L) you need 20 fl oz (606 ml) of 12.5% liquid chlorine, or 26 fl oz (757 ml) of the 10% strength sold in most supermarkets. In granules that same lift is 3.7 oz (104 g) of 73% cal-hypo. Strength is what moves the number, so read the label on the bottle in your hand rather than assuming.

How much baking soda do I need to raise alkalinity?

About 1.4 lb (636 g) of baking soda raises total alkalinity by 10 ppm in 10,000 gal (37,854 L), and it scales straight with both volume and the size of the lift. Aim for the 60–120 ppm band. Baking soda pushes pH up a little as well, so test pH the next day; if it has climbed past 7.8, bring it back down with acid rather than skipping the alkalinity correction.

Why does my chlorine disappear so fast?

Usually stabilizer, and usually in one of two directions. Too little and sunlight destroys free chlorine in hours — an unstabilized outdoor pool can lose most of its chlorine in a single sunny afternoon. Too much and the chlorine is still there but bound: at 30 ppm of cyanuric acid the water needs a minimum of 2.3 ppm free chlorine to stay sanitary, and at 80 ppm it needs 6 ppm to do the same job. People read 2 ppm, call it fine, and get algae. Test cyanuric acid before you blame the chlorine.

How much muriatic acid do I need to lower pH?

There is no single answer, and that is the actual finding. Alkalinity is what resists the move, so taking pH from 7.8 to 7.5 in 10,000 gal needs 7.4 fl oz (218 ml) of 31.45% muriatic acid at 60 ppm alkalinity and 14 fl oz (422 ml) at 140 ppm — 1.9 times as much for the identical pH move. Charts printed as ounces per 0.1 pH ignore that, which is why they underdose high-alkalinity pools and overshoot low-alkalinity ones. Enter your alkalinity and stabilizer readings and the calculator solves the equilibrium instead of guessing.

Can I mix pool chemicals?

No. Never combine pool chemicals with each other — not in a bucket, not in a scoop, not in the skimmer, not in a bin. Cal-hypo and trichlor together can ignite, and acid meeting any hypochlorite releases chlorine gas. Add one chemical to the pool water, run the pump, wait, retest, then consider the next one. Add chemicals to water, never water to chemicals, and store products in separate places.

How much shock does a green pool need?

More than a bag, and the number comes from your stabilizer reading. At 40 ppm of cyanuric acid, clearing algae means holding free chlorine at 16 ppm — from a starting 2 ppm that is 1.6 lb (726 g) of 73% cal-hypo in 10,000 gal. Holding it is the part people skip: test and top back up several times a day, brush the walls, run the pump around the clock, and keep the filter clean until chlorine stops falling overnight. One dose does not clear a green pool.

Does this calculator work in litres and grams?

Yes, natively. Enter the volume in litres and every dose comes back in grams, kilograms and millilitres alongside the US units, and the reference tables below list round metric pool sizes rather than converted gallons — 40,000 L, not 37,854 L. Muriatic acid is computed for the 31.45% (20°Bé) US bottle; if yours is a different concentration, scale by the ratio of strengths.