Pool Volume Calculator: How Many Gallons Is My Pool?
Work out how many gallons your pool holds in seconds. Free pool volume calculator for rectangle, round and oval pools, plus the formulas and measuring tips.
Pool Chemistry Basics: The Ideal Levels Chart
Ideal pool chemistry levels in one chart: pH, free chlorine, alkalinity, calcium, stabilizer and salt, plus what to adjust first and a volume calculator.
Key takeaways
- Keep pH at 7.4–7.6 and free chlorine at 1–3 ppm, higher if your stabilizer level is high.
- Adjust in this order: alkalinity, pH, calcium, stabilizer, then chlorine.
- Test free chlorine and pH two to three times a week during swimming season.
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Clear, comfortable pool water isn’t luck. It comes down to a handful of readings kept inside the right ranges. Get them right and chlorine works efficiently, swimmers’ eyes don’t sting and your plaster, liner and heater last longer. Get them wrong and you pay for it in chemicals, cloudy water and repairs.
The good news: you only need to understand seven numbers, and three of them do most of the work.
The ideal pool chemistry chart
| Reading | Ideal range | Why it matters |
|---|---|---|
| Free chlorine (FC) | 1–3 ppm (more with higher stabilizer) | Kills bacteria and algae |
| pH | 7.4–7.6 (acceptable 7.2–7.8) | Controls chlorine strength and swimmer comfort |
| Total alkalinity (TA) | 80–120 ppm | Buffers pH so it doesn’t swing |
| Calcium hardness (CH) | 200–400 ppm for plaster; about 150–250 ppm for vinyl and fiberglass | Protects plaster and prevents scale |
| Cyanuric acid (CYA, stabilizer) | 30–50 ppm (60–80 ppm for saltwater pools) | Shields chlorine from sunlight |
| Combined chlorine (CC) | Below 0.5 ppm, ideally zero | Chloramines cause the “chlorine smell” |
| Salt (saltwater pools only) | Usually 2,700–3,400 ppm; follow your cell’s manual | Feeds the chlorine generator |
The three readings that matter most
Free chlorine
Free chlorine is the sanitizer that is still available to do its job. The CDC recommends at least 1 ppm in pools (3 ppm in hot tubs; our hot tub chemistry basics cover spa care). In a sunny outdoor pool with stabilizer, aim for the upper end of the range, or use the 7.5% rule above.
pH
pH decides how aggressive your chlorine is and how the water feels. Below 7.2, water becomes corrosive and stings eyes. Above 7.8, chlorine loses much of its punch and scale starts forming. Most pools drift upward over time, especially saltwater pools, so expect to add acid now and then.
Total alkalinity
Alkalinity is pH’s shock absorber. Too low and pH bounces around; too high and pH keeps creeping up no matter how much acid you add. Once it sits between 80 and 120 ppm, it rarely needs attention.
What to adjust first
Chemicals interact, so order matters. Work through them one at a time and retest between steps:
- Total alkalinity — raise with sodium bicarbonate (baking soda), lower with acid and aeration.
- pH — lower with muriatic acid or dry acid (sodium bisulfate); raise with soda ash or aeration.
- Calcium hardness — raise with calcium chloride; lowering it means partially draining and refilling (see our calcium hardness guide).
- Cyanuric acid — raise with stabilizer; the only practical way to lower it is dilution.
- Free chlorine — dose last, once the water is balanced enough for chlorine to work well.
How to test your water
- Test strips are quick and fine for spot checks, but colours are hard to read precisely.
- Liquid drop kits are more accurate. A kit that uses the FAS-DPD method gives exact free and combined chlorine readings, which matters when you are fixing a problem.
- Store testing is useful for a full panel a few times a season, especially for calcium and salt.
Take samples from elbow depth, away from return jets and skimmers. In swimming season, test free chlorine and pH two to three times a week, and alkalinity, calcium and stabilizer every couple of weeks.
How much chemical should you add?
Every dose depends on how many gallons your pool holds, so start by working out your volume.
Pool volume calculator
Measure in feet. For a sloped floor, use the average of the shallow and deep ends.
With your volume known, follow the dosing directions on the product label. A handy benchmark for liquid chlorine: one gallon of 10% liquid chlorine raises free chlorine by roughly 10 ppm in 10,000 gallons of water.
Signs your water is out of balance
| What you see | Likely cause |
|---|---|
| Cloudy or dull water | Low chlorine, high pH or alkalinity, or poor filtration |
| Green tint or slippery walls | Algae growing because chlorine is too low |
| Stinging eyes, strong “chlorine” smell | Combined chlorine (chloramines) or pH out of range |
| White crust at the waterline | High pH together with high calcium |
| Etched plaster, corroded metal | pH or alkalinity too low |
If your pool has already turned green, follow our step-by-step guide to fixing a green pool.
Handling pool chemicals safely
- Always add chemicals to water, never water to chemicals.
- Wear gloves and eye protection when handling acid or chlorine.
- Store chemicals in their original containers, apart from each other, somewhere cool, dry and locked.
- Keep swimmers out while you add chemicals and follow label re-entry times.
And because chemistry is only half of a safe pool, read our guide to the layers of protection every family pool needs.
Frequently asked questions
Is a pH of 7.8 too high?
It is at the top of the acceptable range. The water is still swimmable, but chlorine works noticeably less well, so bring it back toward 7.5.
Why does my pool smell strongly of chlorine?
That smell usually means too little free chlorine, not too much. It comes from chloramines, which form when chlorine reacts with sweat and other contaminants. Shocking the pool breaks them down.
How often should I test my pool water?
Test free chlorine and pH two to three times a week in season, and after heavy use or storms. Test the other readings every two weeks or so.
Sources
Every article is edited by a human and checked against our editorial policy. Spotted a mistake? Tell us.
Keep reading
How to Lower pH in a Pool Without Overshooting
Why pool pH rises, how to lower it safely with muriatic acid or dry acid, how much to add, and how to stop it creeping back up. Step by step, with safety tips.
How to Raise Total Alkalinity in a Pool
Low alkalinity makes pH bounce around and water corrosive. How to raise total alkalinity with baking soda, how much to add and how it differs from raising pH.