How do I calculate the volume of my pool in gallons?

Multiply length × width × average depth in feet, then multiply by 7.48 to get US gallons. For a 16 × 32 ft pool with an average depth of 5 ft, that's 16 × 32 × 5 × 7.48 = 19,148 gallons. For round pools, use π × radius² × depth × 7.48. For oval pools, use π × (length/2) × (width/2) × depth × 7.48.

How many gallons is the average backyard pool?

A typical 16 × 32 ft inground pool with an average depth of 5 ft holds about 19,000 US gallons (72,000 L). A 24-ft round above-ground pool with 4 ft of water holds about 13,500 gallons. Larger family pools (20 × 40 ft) commonly run 30,000–35,000 gallons. Spas and hot tubs are 300–600 gallons.

How much chlorine does my pool need to reach 3 ppm?

Multiply the target rise in ppm × your pool volume in gallons × 0.00013, then divide by the product's chlorine purity (cal-hypo 0.65, dichlor 0.56, trichlor 0.90, sodium hypochlorite 0.125, household bleach 0.06). For a 20,000-gal pool to gain 3 ppm with cal-hypo, that's 3 × 20,000 × 0.00013 / 0.65 ≈ 12 oz. Add gradually with the pump running.

How much shock does my pool need?

Shock dose is typically 10 ppm of free chlorine above your current level — about 1 lb of cal-hypo per 10,000 gallons, or 10 oz of dichlor per 10,000 gallons. After heavy rain, algae blooms, or high swimmer load, you may need a double or triple shock. Always shock at dusk so UV doesn't burn off the chlorine before it can sanitize.

How much salt do I need for a saltwater pool?

Most chlorine generators (SWG) target 3,000–3,400 ppm salt. To raise salinity by 1,000 ppm in 10,000 gallons of water, add about 83 lb of pool salt. For a 20,000-gallon pool going from 0 to 3,200 ppm, that's roughly 533 lb. Salt only needs replacing when water is lost (splash-out, backwash, leaks) — not consumed by the generator.

What is the ideal free chlorine level for a residential pool?

CDC's Model Aquatic Health Code recommends 1–3 ppm free chlorine for residential pools and 2–4 ppm for commercial pools, with pH 7.2–7.8. PWTAG (UK) recommends 1–3 ppm free chlorine for outdoor pools and 1.5–3 ppm for indoor. Anything under 1 ppm risks bacteria; anything over 5 ppm can irritate eyes and skin.

How do I lower the pH in my pool?

Use muriatic acid (31.45% hydrochloric acid) or dry acid (sodium bisulfate). About 1 quart of muriatic acid per 10,000 gallons lowers pH by approximately 0.2 units. Always add acid slowly with the pump running, never pour acid into dry chemicals, and retest after 4–6 hours of circulation before adding more.

How do I raise the alkalinity in my pool?

Add sodium bicarbonate (baking soda). About 1.5 lb of baking soda per 10,000 gallons raises total alkalinity by 10 ppm. Target alkalinity is 80–120 ppm. Raising alkalinity will also nudge pH up slightly, so retest both after circulating for 6 hours and adjust pH separately if needed.

What's the difference between dichlor, trichlor, and cal-hypo?

Dichlor (56% chlorine) is stabilized with cyanuric acid (CYA) and dissolves quickly — good for daily dosing. Trichlor (90%) is also stabilized, very acidic, slow-dissolving — used in floaters and feeders. Cal-hypo (65%) is unstabilized and contains calcium — great for shock but can cloud water in hard-water pools. Sodium hypochlorite (12.5%) is liquid bleach without CYA — easy to dose but expensive per ppm.

What is stabilizer (CYA) and how much do I need?

Cyanuric acid (CYA, stabilizer, conditioner) protects free chlorine from UV degradation in outdoor pools. Target is 30–50 ppm; anything below 30 means chlorine burns off within hours, and anything over 80 ppm reduces chlorine's effectiveness against bacteria. To add 10 ppm of CYA in 10,000 gallons, use about 13 oz of granular stabilizer. CYA only leaves the pool through dilution.

How do I calculate volume for a kidney-shaped pool?

Use the approximation: volume_gal ≈ 0.45 × (L + W) × average_depth × 7.48, where L is the longest length and W the longest width of the kidney shape. For more precise estimates, break the kidney into a large oval plus two semi-circles and sum them. A typical 16 × 32 ft kidney with 5 ft average depth is about 16,200 gallons — roughly 85% of an equivalent rectangle.

How often should I shock my pool?

Weekly during heavy-use summer months, plus after any of: heavy rain, pool party with high swimmer load, water turning cloudy or green, combined chlorine (CC) > 0.4 ppm, or strong chlorine smell (which paradoxically means too LITTLE free chlorine). For lightly-used pools, biweekly may be enough. Always shock at dusk and don't swim until FC drops below 5 ppm.

How do I convert pool gallons to liters?

Multiply US gallons by 3.785 to get liters. Multiply liters by 0.264 to get US gallons. UK (Imperial) gallons differ: 1 Imperial gallon = 1.201 US gallons = 4.546 liters. The calculator displays both US gallons and liters by default since US/UK/CA/AU pool owners use different units — verify which gallon your chemical product label assumes (most US labels assume US gallons).

Does pool water temperature affect chemistry?

Yes. Chlorine demand rises sharply above 85°F because warm water grows algae faster and chlorine evaporates more quickly. Saturation Index (LSI) — which determines whether water is corrosive or scale-forming — depends on temperature, pH, calcium hardness, alkalinity, and CYA. In summer you may need to chlorinate daily; in winter (water below 60°F) you can drop chlorine and pause salt-generator runtime per manufacturer guidance.

Can I use household bleach instead of pool chlorine?

Yes — household bleach (Clorox or store brand, 6% or 8.25% sodium hypochlorite) is chemically the same as pool liquid chlorine (10–12.5%) but more dilute. Avoid 'scented' or 'splashless' versions which contain surfactants. Multiply your liquid pool chlorine dose by the ratio (e.g., for 6% bleach instead of 12.5% pool chlorine, use 2.08× the amount). Bleach is unstabilized — fine for outdoor pools with CYA already in the water.

How much does it cost to fill a pool?

At an average US municipal water rate of $4–$8 per 1,000 gallons, a 20,000-gallon pool costs roughly $80–$160 to fill, plus sewer charges if your utility doesn't offer a 'pool fill' meter exemption. UK water is typically £2–£4 per 1,000 L, so a 75,000-L pool is £150–£300. Some utilities offer one-time exemptions for pool fills — check before opening day to avoid double charges.

Why is my pool cloudy after I shocked it?

Three common causes: (1) Cal-hypo + high calcium hardness → calcium carbonate cloudiness, usually clears in 24–48 hours with filtration. (2) Dead algae from a successful shock — vacuum to waste and run filter 24/7. (3) pH spiked too high after shocking — test pH and add muriatic acid to bring it back to 7.4. Use clarifier or flocculant as a last resort; both add load to the filter.

Is this calculator accurate for above-ground and inground pools?

Yes — the volume formulas are pure geometry and apply to any pool shape regardless of construction type. Above-ground pools are usually round or oval with constant depth. Inground pools often have shallow and deep ends; use the average of the two depths. For freeform or irregular pools (lagoon, freeform with islands), measure several depth points and average them, then apply the kidney approximation as an upper-bound estimate.

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Pool Calculator

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Pool Shape

Measurement Units

Length

Width

Shallow End

Deep End

Chlorine Product

Current FC (ppm)

Target FC (ppm)

Pool Water Volume

21,082 US gal

79,795 liters · 17,557 UK gal · avg depth 5.5 ft

Chemical Doses (Cal-Hypo)

Chlorine to 3 ppm

12.6 oz

Shock dose (10 ppm)

42.2 oz

Salt for SWG (3,200 ppm)

563 lb

CDC MAHC Chemistry Targets

Free Cl: 1–3 ppm

pH: 7.4–7.6

Alkalinity: 80–120 ppm

CYA: 30–50 ppm

Calcium: 200–400 ppm

SWG salt: 3,000–3,400

lightbulb Tips

•Volume gal = L × W × avg depth × 7.48 — measure in feet
•Free chlorine target: 1–3 ppm residential (CDC MAHC)
•Shock = 10 ppm above current FC; add at dusk
•CYA 30–50 ppm protects chlorine from UV burn-off
•SWG salt target: 3,000–3,400 ppm — verify your unit's spec

Pool Calculator

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Chemical Doses (Cal-Hypo)

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