# Pool Calculator

> Calculate pool volume (gallons/liters), chlorine dose, shock, salt for SWG, plus pH and alkalinity adjustments — rectangular, round, oval, kidney.

**URL:** https://calculators.im/pool-calculator  
**Category:** engineering  
**Last updated:** 2026-07-03  

Pool calculator for volume in gallons or liters, chlorine and shock dose, salt for SWG systems, plus pH and alkalinity adjustments. Supports rectangular, round, oval, and kidney pools.

This swimming pool calculator computes water volume by pool shape (rectangular, circular, oval, kidney) in both US gallons and liters, then dosing for free chlorine, shock, salt, pH, alkalinity, and stabilizer (CYA) based on standard pool chemistry. It works for in-ground and above-ground pools and uses the same product purity factors found in CDC's Model Aquatic Health Code and PWTAG technical notes — cal-hypo, dichlor, trichlor, sodium hypochlorite, and liquid bleach. Pool owners use it to figure out how many gallons their pool holds, how much chlorine or shock to add after a heavy rain, how much salt a saltwater (SWG) pool needs to reach 3,200 ppm, and how to raise or lower pH and alkalinity safely.

## Formula

```
Volume_gal = L × W × avg_depth × 7.48   (rectangle)
```

**Variables:**

- **L, W** — Length and width of the pool in feet
- **avg_depth** — (shallow_depth + deep_depth) / 2 in feet
- **7.48** — Cubic feet to US gallons conversion factor

Pool volume in US gallons equals the surface area (length × width for rectangles, π × r² for circles, π × a × b for ovals, ~0.45 × (L+W) × depth for kidney) multiplied by average depth in feet, multiplied by 7.48 gal/ft³. Liters = gallons × 3.785. For chlorine dose, ounces of product = (target_ppm − current_ppm) × volume_gal × 0.00013 / purity, where purity is the active chlorine fraction (cal-hypo 65%, dichlor 56%, trichlor 90%, sodium hypochlorite 12.5%, household bleach 6%).

## Worked Example

### Volume and chlorine dose for a 16 × 32 ft rectangular pool

Average depth = (3 + 8) / 2 = 5.5 ft. Volume = 32 × 16 × 5.5 × 7.48 ≈ 21,082 US gallons (79,795 L). To raise free chlorine by 3 ppm with cal-hypo (65% active): 3 × 21,082 × 0.00013 / 0.65 ≈ 12.6 oz. Shock dose (10 ppm above current FC): 10 × 21,082 × 0.00013 / 0.65 ≈ 42.2 oz of cal-hypo, or use the dichlor-equivalent for stabilized pools.

## How to Calculate Pool Volume and Chemical Dose in 3 Steps

1. **Pick your pool shape** — Choose rectangular, round, oval, or kidney — the calculator switches inputs and applies the right volume formula.
2. **Enter dimensions and water depth** — Length, width (or diameter), shallow-end and deep-end depth. The calculator averages depths automatically for variable-depth pools.
3. **Read volume and chemical doses** — See volume in gallons + liters, plus chlorine, shock, salt, pH, and alkalinity dose suggestions for the pool product you selected.

## Pro Tips

- Measure pool dimensions in feet first, then convert at the end — 7.48 gallons per cubic foot is the canonical US conversion
- Average depth = (shallow end depth + deep end depth) / 2; for a constant-depth pool, just use that depth
- Free chlorine target is 1–3 ppm for residential pools and 2–4 ppm for commercial per CDC MAHC — keep it within this band
- Shock when CC (combined chlorine) exceeds 0.4 ppm or after heavy rain, swimmer load, or algae bloom
- Always pre-dissolve cal-hypo in a bucket of water before adding — never dump granular cal-hypo on a vinyl liner
- Stabilizer (CYA) at 30–50 ppm protects chlorine from UV degradation; too high (>80 ppm) reduces chlorine effectiveness
- Saltwater pool target is 3,000–3,400 ppm salt for most chlorine generators (SWG) — check your unit's spec
- Lower pH with muriatic acid: ~1 quart per 10,000 gal lowers pH by 0.2; raise pH with soda ash, not baking soda
- Raise alkalinity 10 ppm per 10,000 gal with ~1.5 lb of sodium bicarbonate (baking soda)
- Wait at least 30 minutes between adding different chemicals; run the pump while dosing

## Frequently Asked Questions

### 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.

## Deep Dive

Calculate pool volume in US gallons and liters, then dose chlorine, shock, salt for saltwater (SWG) systems, pH, alkalinity, and stabilizer (CYA) — all in your browser, with no data sent to a server. Supports rectangular, round, oval, and kidney pools, both inground and above-ground. Built on standard pool chemistry from CDC's Model Aquatic Health Code (US), PWTAG technical notes (UK), Health Canada recreational water guidelines, and Royal Life Saving Australia. Below: 12 sections cover volume formulas, chlorine product math, shock dosing, salt for SWG pools, pH and alkalinity adjustments, CYA stabilizer levels, and a weekly maintenance checklist.

### Pool Volume Calculator: Gallons and Liters by Pool Shape

**Pool volume** is the foundation of every chemistry dose — get it wrong by 20% and your chlorine, shock, and salt amounts are wrong by the same factor.

The calculator uses four geometry formulas:

- rectangular pools = L × W × average_depth × 7.48
- round pools = π × radius² × depth × 7.48
- oval pools = π × (length/2) × (width/2) × depth × 7.48
- kidney pools ≈ 0.45 × (L + W) × average_depth × 7.48

All inputs are in feet; the 7.48 factor converts cubic feet to US gallons. Results are shown in both US gallons (used by most US/CA chemical labels) and liters (UK/AU). Multiply gallons × 3.785 to convert to liters, or × 0.832 to convert to UK Imperial gallons.

### How Many Gallons in My Pool: Rectangular Pool Formula

For a **rectangular pool** with variable depth (shallow end to deep end), use average_depth = (shallow_depth + deep_depth) / 2.

- A 16 × 32 ft pool with a 3 ft shallow end and an 8 ft deep end has an average depth of 5.5 ft, so volume = 16 × 32 × 5.5 × 7.48 ≈ 21,082 US gallons (79,795 L).
- A 20 × 40 ft pool with 4 ft average depth holds 23,936 gallons.
- A constant-depth 12 × 24 lap pool at 4 ft holds 8,617 gallons.

For pools with a hopper or shallow ledge, take measurements at three or four points along the bottom and average them — small errors here scale into the chemical dose.

### Round Pool Calculator: Above-Ground Pool Volume in Gallons

**Round above-ground pools** dominate the budget end of the market — Intex, Bestway, Coleman 12-, 15-, 18-, 21-, 24-, and 30-foot rounds. Volume = π × (diameter/2)² × depth × 7.48.

- A 24-foot round with 52-inch sidewalls (4.33 ft) filled to 4 ft of water holds 13,562 US gallons (51,338 L).
- An 18-foot round at 4 ft water depth holds 7,646 gallons.
- A 30-foot round at 4 ft holds 21,243 gallons.

Manufacturer specs sometimes use full sidewall height — always measure actual water depth, which is typically 6 inches below the top rail because of the skimmer cutout.

### Oval and Kidney Pool Calculator: Shape Volume Formulas

**Oval pools** use volume = π × (length/2) × (width/2) × depth × 7.48 — for a 16 × 32 ft oval at 4.5 ft depth: π × 8 × 16 × 4.5 × 7.48 ≈ 13,535 gallons.

**Kidney pools** are harder; the approximation volume_gal ≈ 0.45 × (L + W) × average_depth × 7.48 treats the kidney as roughly 85% of the enclosing rectangle.

For more precise estimates, break the shape into a primary oval plus two end semi-circles and sum the volumes, then add a small correction for the inward curve (typically −5% to −10%). Most pool stores accept the approximation for chemistry purposes since chlorine and shock have wide tolerance bands.

### Pool Chlorine Calculator: Dose to Reach Target Free Chlorine

To raise **free chlorine (FC)** by N ppm in a pool of V gallons using a product with chlorine purity P (as a decimal): dose_ounces = N × V × 0.00013 / P. The constant 0.00013 comes from converting ppm (mg/L) to ounces per gallon.

Product purities:

- calcium hypochlorite (cal-hypo) = 0.65
- sodium dichloroisocyanurate (dichlor) = 0.56
- trichloroisocyanuric acid (trichlor) = 0.90
- sodium hypochlorite (liquid pool chlorine) = 0.125
- household bleach = 0.06 (6%) or 0.0825 (8.25%)

Example: raise FC by 2 ppm in 20,000 gallons with cal-hypo: 2 × 20,000 × 0.00013 / 0.65 ≈ 8 oz. Always pre-dissolve cal-hypo in a bucket and add slowly with the pump running.

### Pool Shock Calculator: How Much Shock Does My Pool Need?

**Shock dose** targets 10 ppm of free chlorine above the current level — enough to oxidize combined chlorine (chloramines) and kill algae.

Using cal-hypo: 1 lb (16 oz) of 65% cal-hypo per 10,000 gallons raises FC by about 7.5 ppm. So a 20,000-gal pool needs about 2.7 lb of cal-hypo for a standard 10 ppm shock. Dichlor (56%) needs 1.2 lb per 10,000 gal for the same 10 ppm.

After an algae bloom, double or triple the dose (20–30 ppm shock). Shock at dusk so UV doesn't burn off the chlorine before it sanitizes. Don't swim until FC drops below 5 ppm — usually overnight with the pump running.

### Pool Salt Calculator for Saltwater (SWG) Pool Systems

**Saltwater pools** use a chlorine generator (SWG) that electrolyzes dissolved salt into chlorine — typical salinity target is 3,000–3,400 ppm depending on the unit (Hayward AquaRite, Pentair IntelliChlor, Jandy AquaPure, CircuPool).

To raise salinity by 1,000 ppm in 10,000 gallons of water, add 83 lb of pool salt (sodium chloride, 99%+ purity). For a 20,000-gallon pool starting at 0 ppm and targeting 3,200 ppm: 3.2 × 20,000 × 8.34 / 1,000,000 × 1,000 ≈ 533 lb of salt (12 standard 40-lb bags).

Salt is only lost through splash-out, backwash, and leaks — not consumed by the generator. Always test salinity before adding more.

### Pool pH and Alkalinity Calculator: Muriatic Acid & Baking Soda

Pool **pH** should stay between 7.2 and 7.8 (ideal 7.4–7.6); **total alkalinity** 80–120 ppm.

- To lower pH: 1 quart of muriatic acid (31.45% HCl) per 10,000 gallons lowers pH by approximately 0.2 units and total alkalinity by about 10 ppm. Dry acid (sodium bisulfate) at 1.5 lb per 10,000 gallons does similar.
- To raise pH only (without changing alkalinity much): use soda ash (sodium carbonate) at 6 oz per 10,000 gallons to raise pH by about 0.2.
- To raise alkalinity 10 ppm in 10,000 gallons: 1.5 lb of baking soda (sodium bicarbonate).

Always retest after 6 hours of circulation and adjust pH and alkalinity in separate sessions, never simultaneously.

### Pool Stabilizer Calculator: CYA Levels for Outdoor Pools

**Cyanuric acid** (CYA, stabilizer, conditioner) acts as a UV shield for free chlorine in outdoor pools. CDC MAHC recommends 30–50 ppm for manually-dosed pools and 60–80 ppm for SWG-generated pools (because lower-output generators benefit from longer chlorine residence time).

Below 30 ppm, free chlorine burns off in 1–2 hours of summer sun. Above 80 ppm, the chlorine-CYA equilibrium reduces hypochlorous acid (the active killer) and bacteria killtimes balloon.

To raise CYA 10 ppm in 10,000 gallons, add 13 oz of granular stabilizer (broadcast in front of return jets or place in skimmer sock — never dump granular CYA directly on liner). CYA only decreases through dilution (rain overflow, splash-out, backwash, drain-and-refill).

### Pool Water Balance Guide: Ideal Free Chlorine, pH, Alkalinity

**Target ranges for residential pools** (CDC MAHC + PWTAG + Health Canada consensus):

- Free chlorine 1–3 ppm (2–4 ppm during heavy use)
- combined chlorine < 0.4 ppm (shock if higher)
- pH 7.4–7.6 (acceptable 7.2–7.8)
- total alkalinity 80–120 ppm
- calcium hardness 200–400 ppm
- CYA 30–50 ppm (60–80 for SWG)
- salinity 3,000–3,400 ppm (SWG only)

Test free chlorine + pH 2–3 times per week, full panel (alkalinity, CYA, calcium, salinity) weekly during summer and biweekly off-season. DPD-based test kits and Taylor K-2006/K-2005 are the standard; test strips are convenient but less accurate above 5 ppm chlorine.

### Pool Maintenance Checklist: Weekly, Monthly, Seasonal Tasks

- **Weekly:** test FC + pH and dose to target; skim surface; vacuum or robot-clean; brush walls and tile line; empty pump and skimmer baskets; check filter pressure (clean when 8–10 psi over baseline).
- **Monthly:** full chemistry panel (alkalinity, CYA, calcium, salinity if SWG); inspect O-rings and gaskets; backwash sand or DE filter; check pool light, ladder, and handrail bolts.
- **Seasonal:** spring opening (uncover, reconnect plumbing, shock, balance over 3–5 days before swimming); fall closing (drop pH to 7.2, super-shock, add winterizing algaecide, blow out lines, lower water below skimmer, cover).

Save chemistry logs each season — pattern recognition saves chemicals and identifies leaks early.

### Pool Volume Conversion: US Gallons to UK Gallons and Liters

Pool chemistry labels around the English-speaking world use different units, and using the wrong one over-doses or under-doses your pool.

- **US gallons** (3.785 L) are standard for US and Canadian residential pool products.
- **UK (Imperial) gallons** (4.546 L) appear on some UK pool chemistry containers — 1 UK gallon = 1.201 US gallons, so a 20,000-US-gal pool is only 16,652 UK gallons.
- Australia and most of the EU/UK commercial sector use **liters** directly; 20,000 US gal = 75,708 L.

Always check whether the product label says 'gallons' (US), 'Imp gal' (UK Imperial), or 'L' (metric) before computing dose. This calculator displays both US gallons and liters so you can apply the right unit to your product.

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## Authoritative Sources

- [CDC Model Aquatic Health Code (US)](https://www.cdc.gov/mahc/index.html) — US Centers for Disease Control authoritative guidance for pool and spa operation, including free chlorine targets, pH, and CYA limits
- [EPA Pool Pesticide & Chemical Guidance (US)](https://www.epa.gov/pesticide-registration/pesticide-registration-manual-chapter-12-antimicrobial-products) — US Environmental Protection Agency rules for antimicrobial pool chemicals — cal-hypo, dichlor, trichlor labelling and dosing
- [PWTAG Pool Water Treatment Advisory Group (UK)](https://www.pwtag.org/technical-notes/) — UK/international technical notes on free chlorine, combined chlorine, pH, alkalinity, and CYA targets used by commercial pool operators
- [HSE UK — Managing Health and Safety in Swimming Pools](https://www.hse.gov.uk/pubns/books/hsg179.htm) — UK Health & Safety Executive HSG179 guidance for pool water quality, plant operation, and chemical handling
- [Health Canada — Recreational Water Quality Guidelines](https://www.canada.ca/en/health-canada/services/publications/healthy-living/guidelines-canadian-recreational-water-quality-third-edition.html) — Health Canada third edition guidelines for chemical disinfection, pH range, and recreational water safety
- [Royal Life Saving Australia — Guidelines for Safe Pool Operation](https://www.royallifesaving.com.au/research-and-policy/aquatic-industry-research) — Royal Life Saving Australia and NHMRC guidance on pool water quality, chemical handling, and supervisor training

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