Everything Here Is Your Volume, Times Something
Pool chemistry is less mysterious than it looks. Almost every reading is in parts per million, one part per million is one milligram per litre, and so every dose you will ever calculate is the same shape: how far the reading has to move, multiplied by how much water you have, divided by how concentrated the product in your hand is. That is it. The reason pool advice feels like folklore is that most of it skips the middle term and quotes a dose for a pool that is not yours.
Which is why these four pages share one number. Measure your pool once on the volume calculator, and it stays in your browser for the others to pick up.
Which Calculator for Which Job
They divide by the question you arrived with, not by the chemical. Name the question and the choice makes itself.
- “How much water is in this thing?” The pool volume calculator handles rectangles, rounds, ovals and kidney or freeform pools, measured in feet or meters, and answers in US gallons and litres at once. Three of those four shapes are exact geometry; the freeform one uses the 0.45 × (width A + width B) × length estimate manufacturer worksheets print, and says so. Start here even if you think you know the number — the figure printed on the box a pool came in assumes a fill depth almost nobody actually runs.
- “My test kit says these numbers. Now what?” The pool chemical calculator is the everyday one: free chlorine, pH, total alkalinity and stabilizer in one pass, each dose sized for the product you actually own — liquid chlorine at 10% or 12.5%, cal-hypo at 65% or 73%, dichlor, trichlor, soda ash, muriatic acid, baking soda. Shock is not a separate page here because it is not separate chemistry: it is the same chlorine dose aimed at a higher target.
- “My generator is complaining about salt.” The pool salt calculator turns a current and target salinity into pounds, kilograms and whole bags — 40 lb or 25 kg, rounded up, because half a bag is not a purchase. It also handles the direction people do not expect: if you are already over target it tells you so and works out how much water has to be replaced, because nothing removes salt.
- “My chlorine keeps vanishing” — or “my CYA is 90.” The cyanuric acid calculator covers the reading that quietly governs the others. Stabilizer protects chlorine from sunlight, and the amount of chlorine your pool needs scales with how much of it you have — which is why a pool at 80 ppm CYA and a pool at 30 need genuinely different chlorine targets. It sizes a dose to raise it, tells you the share of water to replace to lower it, and shows the chlorine range that level implies.
Where the Numbers Come From
Every dosing figure in the tables on these pages is computed from the same functions the tools run, so a table and the tool can never disagree about the same pool. One part per million is one milligram per litre, corrected for each product’s available chlorine or active fraction — and the pH dose is solved from the carbonate and cyanurate buffer system rather than read off a fixed table, which is why the acid a pH move needs here changes when your alkalinity or stabilizer changes. A printed “ounces per 0.1 pH” chart cannot do that, and can be off by a factor of two on a pool at the edges of the normal range.
Two figures in the chlorine-versus-stabilizer table are the exception, and they are marked where they appear: the everyday band and the algae level both stop scaling at the bottom of the range and follow the floors the published FC/CYA chart prints, because a fraction of a very small stabilizer reading is less chlorine than any pool needs to work.
More broadly, where a page quotes something that is not arithmetic — a common cable length, a coverage rate, an area approximation, a band published on a chart rather than derived — it says so at the point it says it. Those are the figures worth arguing with, and the robot cleaner guide keeps a list of its own at the foot of the page.
What These Will Not Do
They do not diagnose your water. A calculator turns a reading into a dose; it has no idea your filter is short-cycling, your cell is scaled, or the reading you typed came from a strip that expired last summer. Nor do they track anything over time. Your pool and the readings you type are kept in your own browser so a page opens where you left it, and nowhere else — there is no account to sign into and nothing is sent anywhere.
Three habits are worth more than any of the arithmetic: test before you dose, add one chemical at a time with the pump running, and re-test after a full turnover instead of stacking a second dose on top of a first. Never mix two chemicals together outside the pool — two different chlorine products in one bucket is a genuinely dangerous combination, and it is the one mistake here with consequences worse than cloudy water.