About Pool Ratio

Pool Ratio answers the question every pool owner has after testing the water: what do I add, how much of the product I actually have, and in what order?

Pool Ratio is an independent website from the same small publisher as Supply Math (free material calculators for home and yard projects) and Tire Ruler (free tire size tools). It isn’t owned by a chemical maker or pool store, and no brand pays to change the results.

What we promise

• Fast and free. No sign-up, nothing to install. The tools run in your browser, and what you type is never sent to us.
• Show the math. Every page explains the formula and works an example, so you can check it yourself.
• Safety over speed. pH doses come with “add about ¾ and retest”, and we never suggest mixing products.
• Clean ads. When the site shows ads, they’ll stay out of the way: no pop-ups, and never inside the tools.

How we calculate

• Volume: surface area × average depth, where average depth = (shallow + deep) ÷ 2. Round: π × radius²; oval: π × half-length × half-width; kidney: 0.45 × (width A + width B) × length. 1 cubic foot = 7.48 US gallons; 1 US gallon = 3.785 litres.
• Chlorine: product strength is grams of available chlorine per 100 mL (liquids, “trade percent”) or percent by weight (solids). 1 ppm = 1 mg per litre. Trichlor adds about 0.6 ppm stabilizer and dichlor about 0.9 ppm per ppm of chlorine; cal-hypo adds about 0.7 ppm calcium.
• Chlorine targets follow the widely used chlorine-to-stabilizer relationship: minimum free chlorine ≈ 7.5% of CYA, target ≈ 11.5%, shock ≈ 40%.
• pH: a carbonate and cyanurate buffer model works out how much acid or soda ash moves pH from your reading to your target, given your alkalinity and stabilizer. With no stabilizer our doses agree within about 5% with the empirical pH fit published by Trouble Free Pool; with stabilizer at 30–70 ppm we give 15–35% more, because cyanurate buffers pH too. Flat label charts ignore both and usually say less. That is why every pH dose says to add about three quarters, circulate and retest.
• Alkalinity, calcium, stabilizer, salt: by molecular weight. Baking soda: 1.68 mg per litre per ppm of alkalinity; calcium chloride: 1.11 mg (pure) per ppm of hardness, adjusted for 77% flake or 94% anhydrous; cyanuric acid: 1 mg per ppm; salt: 1 mg per ppm.
• Lowering salt, stabilizer and calcium: only replacing water works. Drain fraction = 1 − target ÷ current (for refill water with none in it).
• Pool sizes: 28 common above-ground and in-ground sizes, at 4 ft of water for above-ground pools and 3.5 → 6 ft for in-ground rectangles.

Test kits have error (strips more than drop tests), product strengths fade with age and heat, and real pools differ from their nominal size. Treat any dose as a starting point and retest.

Not professional advice

Pool Ratio is for general guidance. Follow the label on every product, which is the legal instruction for its use. For a commercial or public pool, follow your local health code and a certified operator.

Corrections

If a result looks wrong, tell us the page, your inputs and what you expected: hello [at] poolratio.com. We check every report and fix confirmed errors quickly. The calculations are covered by automated tests.

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