How we calculate
Every result on this site can be traced to a formula and a published source. This page explains how.
Sources
Pool and spa water-chemistry targets and dose rates come from industry and public-health references, product labels and safety data sheets, and established water-chemistry guides. Equipment sizing comes from manufacturer data sheets and government energy guidance. Cost ranges come from published national cost surveys, adjusted by state. Aquarium figures come from manufacturer specifications and fish-keeping references. Each calculator lists its sources with links under the result.
The math on every page
Each result shows the formula with your own numbers substituted, so you can check it with a pencil. The text below each calculator explains the formula in plain language with a worked example, and the examples are part of our automated tests, so the text and the calculator cannot drift apart.
Your pool, saved on your device
Every chemistry, heater and cost calculator starts from your pool volume. Enter it once, or work it out from the shape and depth, and it is remembered in your browser for the other calculators. It never leaves your device.
Units, rounding and dosing
Switch between US gallons, pounds and ounces and litres, kilograms and grams at any time. Internally every calculator works in metric units and converts only for display. Things you buy, such as jugs, bags and boxes, are rounded up to the next whole unit, and the exact dose is shown as well. Doses assume the product strength you select. Chemical results tell you how much to add for the change you want; retest after the water has circulated, because test kits, water and products vary.
Where authorities disagree
Recommended ranges are not identical everywhere. Where a target differs between sources, for example the free chlorine needed for a given stabilizer level, the page says which one it follows and why.
Cost estimates
Cost calculators combine published national cost ranges with state factors: labor from Bureau of Labor Statistics wage data and materials from Bureau of Economic Analysis regional price parities. They give a low, typical and high range and are planning figures, not quotes; get at least three written bids for work you hire out.
Review
Our editorial team checks each calculator against its sources before publishing and again when guidance changes. The date of the last review is shown on every calculator page.
Limits
Results are estimates for planning and buying, not professional, medical or engineering advice. Pool and spa chemicals are hazardous: follow the product label, never mix products, and keep them away from children and pets. A licensed pool professional, your local health department and your building department decide what applies to your pool.
Corrections
If you find an error, email jonas@sport-calculator.com. We fix confirmed errors and update the review date.