Pool and hot tub calculators
Every calculator here runs on the same tested formulas, works with the products you already have, and shows its math on the methodology page. Not sure where to start? Enter your latest test in the pool chemical calculator: it tells you what to add first.
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.
Chemical dosing calculators
The full chemical calculator turns one test into an ordered plan: chlorine, alkalinity, pH, calcium, stabilizer, and salt. If you only need one product, open the dosing section: it has a calculator per product (liquid chlorine, bleach, acid, baking soda, stabilizer, and salt) and ready-made dose charts for 16 pool sizes. Single-task calculators with their own guides: liquid chlorine, chlorine tablets per week, soda ash to raise pH, baking soda to raise alkalinity, and acid to lower alkalinity.
Volume calculators by shape
Every dose depends on gallons, so get this number right once. Use the pool volume calculator for rectangle, round, oval, kidney, and L-shaped pools, or go straight to the round, oval, or kidney-shaped versions. Above-ground pools hold less than the box size suggests. The calculators correct for that.
Water balance: FC/CYA and LSI
Two numbers explain most "my chemicals are fine but the water isn't" problems. The chlorine level calculator shows the minimum and target free chlorine (FC) for your stabilizer (CYA) level. The LSI calculator (Langelier Saturation Index) tells you whether your water tends to etch plaster or leave scale, based on pH, temperature, calcium, and alkalinity.
Equipment and cost calculators
How long to run the pump, what heating costs, and what your chlorine really costs per ppm: see the pump run time, heater cost, heater size, chemical cost, and fill cost calculators. They use example rates by default, so enter the numbers from your own bills and equipment labels.
Hot tub calculators
The hot tub chemical calculator accepts 50 to 1,500 gallons and gives small doses in teaspoons and grams. Hot tub pages for chlorine, bromine, shock, pH, and alkalinity are listed below.
In this section
Calculators
- Pool chemical calculatorFree pool chemical calculator: enter pool size and one test (FC, pH, TA, CYA, CH, salt) and get doses for…
- Pool volume calculator (gallons and liters)How many gallons is your pool?
- Round pool gallons calculatorHow many gallons in a round pool: enter diameter and depth (or wall height) and get gallons and liters.
- Oval pool gallons calculatorOval pool volume in gallons.
- Pool LSI calculatorCalculate your pool's Langelier Saturation Index from pH, temperature, calcium, alkalinity, CYA, and TDS,…
- Kidney shaped pool volume calculatorGallons in a kidney shaped pool from its length and two widths, with sloped floor support.
- How long to run your pool pumpHow many hours to run your pool pump: turnover math from your gallons and pump flow, variable-speed tips,…
- Pool heater cost calculatorEstimate what it costs to heat your pool: gallons, temperature rise, heater type, and your local gas or…
- Pool heater size calculatorWhat size heater your pool needs: BTU for your gallons and how fast you want to heat, plus surface-area…
- Pool chemical cost calculatorCompare the real cost of chlorine: price per ppm per 10,000 gallons for liquid chlorine, bleach, tablets,…
- How much does it cost to fill a pool?What it costs to fill your pool: gallons × your water rate (and sewer), or the truck delivery quote per load.
Dosing calculators
- How much chlorine to add to your poolHow much chlorine to add to a pool: 1.3 fl oz of 10% liquid chlorine per 1,000 gallons raises FC 1 ppm.
- Liquid chlorine calculatorHow much liquid chlorine to add: 12.8 fl oz of 10% raises 10,000 gallons by 1 ppm.
- Muriatic acid calculatorHow much muriatic acid (31.45% or 14.5%) to lower pH or alkalinity, based on your TA and CYA, not a rule of…
- How much baking soda to add to your poolBaking soda dose to raise alkalinity for your pool size, how much it moves pH, and when to use soda ash…
- Pool stabilizer calculatorHow much stabilizer (cyanuric acid) to add for your pool size and target, how long it takes to dissolve, and…
- Pool salt calculatorHow much salt to add to your salt water pool for your chlorinator's target ppm.
- How much bleach to add to your poolPlain unscented bleach works as pool chlorine.
- How many chlorine tablets does your pool need?How many 3-inch chlorine tablets your pool needs: about 4.4 a week for 15,000 gallons losing 2 ppm a day.
- Borax in your poolIs borax good for pools?
Chemistry calculators
- What should your pool chlorine level be?The ideal pool chlorine level depends on stabilizer: 3–5 ppm free chlorine at 40 ppm CYA.
- How to lower pH in a poolLower pool pH with muriatic acid or dry acid: exact dose for your TA and CYA, why pH keeps rising, and how…
- How to raise pH in a poolRaise pool pH with soda ash (pH increaser) or aeration.
- How to raise alkalinity in a poolRaise pool alkalinity with baking soda: 1.4 lb per 10,000 gallons adds 10 ppm TA.
- How to lower alkalinity in a poolLower pool alkalinity with muriatic acid in rounds, then aerate: 26 fl oz of 31.45% acid per 10,000 gallons…
- How to lower cyanuric acid in a poolThe only reliable way to lower CYA is replacing water.
- Calcium hardness: levels and how to raise itWhat calcium hardness should be for plaster vs vinyl pools, what it does, and how much calcium chloride to…
- How to lower calcium hardnessHigh calcium can only be diluted.
Hot tub calculators
- Hot tub chemical calculatorHot tub and spa chemical calculator for 50–1,500 gallons: chlorine or bromine, pH, alkalinity, calcium.
- How much chlorine to add to a hot tubChlorine dose for 200–700 gallon hot tubs with dichlor granules, liquid chlorine, or bleach.
- Hot tub bromine: levels, start-up and dosingBromine levels (4–6 ppm), how to start a hot tub on bromine, how many tablets for your floater, and why…
- How to shock a hot tubHow much shock to add to your hot tub, when to use chlorine shock vs MPS (non-chlorine), and how long to…
- How many gallons is a hot tub?Most hot tubs hold 200–600 gallons: 217–245 for 3 seats, 314–455 for 5–9 seats in our sample.
- How often to change hot tub waterHow often to drain your hot tub based on its gallons and how many people soak each day, plus signs you need…