About Easy Pool Calc

Easy Pool Calc is a set of free calculators for swimming pools and hot tubs: pool volume for any shape, chlorine, shock, salt, pH, alkalinity, calcium and stabilizer doses, the saturation index, pump and filter sizing, heater size and heat-up time, and the cost of running it all. Each one shows the formula it uses, so you can check the math against your own numbers before you pour anything into the water.

The numbers are planning estimates. Chemical doses are worked out from the strength printed on the product label and simple chemistry; real products, test kits and pools all vary, so every dosing calculator tells you to add the chemical, let it circulate and retest. Recommended levels come from named public sources — the CDC’s Healthy Swimming guidance and Model Aquatic Health Code, US Department of Energy pages for pumps, heaters and covers — and equipment figures come from manufacturers’ manuals. Where a figure is a hobbyist convention rather than an official one, such as the Trouble Free Pool chlorine-to-stabilizer chart, the page says so. The product label is the law for pool chemicals: always follow it.

It is part of a small family of free project calculators that began with Easy Scale Calc (opens in a new tab). The site is supported by advertising and by Amazon affiliate links on product recommendations (as an Amazon Associate it earns from qualifying purchases); neither changes what the calculators say. If you spot an error or want a calculator added, use the contact page.

How we build and check the calculators

• Every calculator runs entirely in your browser — nothing you type is sent anywhere.
• Each page shows its formula, and every result shows the working with your own numbers, so you can check it by hand.
• Chemical doses are worked out from the strength on the product label and the chemistry of the compound (1 ppm is 1 milligram per litre). They are estimates: every dosing calculator says to add the chemical, let it circulate and retest — and to follow the label, which is the law for pool sanitizers.
• Recommended levels come from the CDC’s Healthy Swimming pages and the Model Aquatic Health Code; equipment figures (filter sand, pump and heater sizing) come from manufacturers’ manuals and US Department of Energy guidance, linked on each page. Hobbyist conventions, such as the Trouble Free Pool chlorine-to-stabilizer chart, are named as such.
• Every calculator is tested in both US and metric units, and every worked example is recomputed at build time so the numbers on the page always match the calculator.

How this content is made

The calculators, worked examples and guides on this site were drafted with the help of AI tools and then checked in several passes. Every number on a worked-example page is recomputed from the calculator at build time, so the text and the calculator can’t disagree. Formulas and published figures (CDC and Model Aquatic Health Code levels, product-label strengths, manufacturers’ manuals, Department of Energy guidance) are checked against the linked sources.

Automated checks run on every build: each calculator is tested in US and metric units and unit switching must round-trip exactly. If you find an error, tell us — corrections are fixed and logged below.

Sources we use

• NIST Handbook 44, Appendix C — General tables of units of measurement (opens in a new tab) — 1 US gallon = 231 cubic inches (7.48052 gallons per cubic foot).
• Intex — Ultra XTR Frame 24 ft × 52 in pool (product page) (opens in a new tab) — Lists a water capacity of 12,481 gallons for a 24 ft × 52 in pool; the fill depth is not stated.
• Intex — Ultra XTR Frame 18 ft × 52 in pool (product page) (opens in a new tab) — Lists 6,981 gallons.
• Intex — Ultra XTR Frame 16 ft × 48 in pool (product page) (opens in a new tab) — Lists “5,061 gallons (90%)” — capacity at 90% of the wall height.
• Supplemental above-ground pool base instructions (opens in a new tab) — The bottom track must rest on solid ground, not fill or sand; a 2 in thick, level bed of sand; cove at least 6 in up the wall and 6 in out.
• Uni-Bead liner installation instructions (opens in a new tab) — A 2 in layer of brick sand over the entire foundation inside the base rails; cove about 8 in high and 8 in wide.
• Swimline above-ground liner instructions (opens in a new tab) — Clear grass and roots within the pool area and 1 foot beyond; spread a 2 in layer of mason sand; do not use beach or play sand; form a 6 in × 6 in cove.
• Doughboy above-ground pool installation manual (opens in a new tab) — Do not use materials that shift in the cove, like sand, or the pool may eventually rupture (it uses screened damp earth or a preformed cove); base level within 1 in from side to side.
• Swimline — frequently asked questions (opens in a new tab) — The liner should sit on top of a 4–6 inch cove.
• Leslie’s — Alkalinity Up (sodium bicarbonate) label (opens in a new tab) — 100% sodium bicarbonate; 1-1/2 lb per 10,000 gallons raises total alkalinity about 10 ppm.
• CDC — Model Aquatic Health Code, 5th edition (2024), code (opens in a new tab) — Free chlorine minimum 1.0 ppm (2.0 with CYA, 3.0 in spas); pH 7.0–7.8; CYA at or below 90 ppm; CYA:FC above 45:1 is an imminent hazard; TA 60–180 ppm; turnover tables.
• CDC — Model Aquatic Health Code, 5th edition (2024), annex (opens in a new tab) — CYA reduces chlorine’s effectiveness; correcting total alkalinity for CYA by subtracting CYA ÷ 3.
• USGS — Alkalinity calculator: methods (opens in a new tab) — Temperature-dependent equilibrium constants for water and carbonic acid (after Stumm & Morgan), with activity corrections.
• CDC Healthy Swimming — Home pool and hot tub water treatment and testing (opens in a new tab) — pH 7.0–7.8; free chlorine at least 1 ppm in pools (2 ppm with cyanuric acid) and 3 ppm in hot tubs; no CYA in hot tubs; test twice a day.
• CDC — Pool chemical injuries press release (2014) (opens in a new tab) — Never mix pool chemicals, especially chlorine products with acid; add chemical to water, never water to chemical.
• OxyChem — Calcium chloride for pools and spas (opens in a new tab) — Pool grades: anhydrous 94–97% mini-pellets and 83–87% granular/flake; “One pound of calcium chloride raises the hardness of 10,000 gallons of water by approximately 10 ppm.”
• Leslie’s — Hardness Plus label (opens in a new tab) — “Adding 1.25 pounds of hardness plus to 10,000 gallons of water will raise the calcium hardness by 10 ppm.”
• Taylor Technologies — Using the Taylor circular Watergram (opens in a new tab) — Saturation index = pH + temperature factor + log CH + log carbonate alkalinity − constant; within ±0.5 of zero needs no adjustment.
• US EPA label 57787-18 — calcium hypochlorite 65% (opens in a new tab) — 65% available chlorine; 2 oz per 10,000 gallons raises chlorine about 1 ppm; superchlorinate with 10 oz per 10,000 gallons.
• Trouble Free Pool (hobbyist forum wiki) — CYA/chlorine relationship (opens in a new tab) — A widely used hobbyist convention, not an official standard: minimum FC 7.5% of CYA, SLAM (shock) level 40% of CYA, salt-water pools 5%.
• Trouble Free Pool — The free chlorine and cyanuric acid relationship (chart) (opens in a new tab) — The same convention as a chart, with a separate table for salt-water pools.
• Michigan Administrative Code R 325.2194 — swimming pool chemical levels (opens in a new tab) — An example of a state rule that raises the chlorine minimum as CYA rises: 2.0 mg/L at 20–40 ppm CYA (pH 7.2–7.5), plus 0.5 mg/L for each further 20 ppm, CYA no more than 80.
• US EPA label 36284-5 — 3 in trichlor tablet (7 oz) (opens in a new tab) — 90% available chlorine; one tablet gives 4.7 ppm in 10,000 gallons; 1 tablet per 8,000 gallons every 7–14 days to maintain.
• ICC Building Safety Journal (PHTA Recreational Water Quality Committee) — Trichlor: the dependable pool performer (opens in a new tab) — Trichlor is 90% available chlorine and adds 0.6 ppm cyanuric acid for each ppm of chlorine.
• Leslie’s — In The Swim 3 inch chlorine tablets (50 lb) (opens in a new tab) — 99% trichlor, 90% available chlorine, about 100 tablets per 50 lb; gives both “one tablet per 10,000 gallons” and “one 3 inch tablet for every 5,000 gallons” as weekly rates.
• CDC — Pool chemical safety: storage poster (opens in a new tab) — Separate acid and chlorine; don’t mix different types of chlorine; keep chemicals cool, dry and in original containers.
• CDC Healthy Swimming — Staying healthy in hot tubs (opens in a new tab) — No hotter than 104°F (40°C); chlorine at least 3 ppm, bromine 4–8 ppm, pH 7.0–7.8; no children under 5.
• CDC Healthy Swimming — Operating public pools, hot tubs and splash pads (opens in a new tab) — Hot tubs: at least 3 ppm free chlorine or 4 ppm bromine; water no hotter than 104°F (40°C).
• Leisure Time — Spa 56 chlorinating granules (dichlor) label (opens in a new tab) — 99% sodium dichlor dihydrate, 55% available chlorine; ½ oz per 500 gallons for a 2–3 ppm residual; 1 oz per 500 gallons to shock.
• Leslie’s — Chlor Brite spa shock (dichlor) label (opens in a new tab) — Half an ounce per 500 gallons; 1.5 oz per 500 gallons after use.
• Leisure Time — Reserve (sodium bromide) label (opens in a new tab) — Sodium bromide 32.18%; 4 oz per 250 gallons at start-up; 1 oz per 250 gallons weekly.
• Leslie’s — Bromine Tabs Plus label (opens in a new tab) — 98% active ingredient; 3 tablets per 300 gallons in a floater or feeder.
• SpaGuard — Brominating Tabs (opens in a new tab) — BCDMH 98%; target active bromine 3–6 ppm.
• OxyChem — Soda Bleach Solutions Handbook (re-hosted copy) (opens in a new tab) — Trade percent = grams per litre of available chlorine ÷ 10; weight % NaOCl ≈ 1.05 × weight % available chlorine; strength and specific gravity table.
• US EPA reg. 42177-80 — sodium dichlor label (ProPools copy) (opens in a new tab) — Dihydrate, 56% available chlorine; 2–3 oz per 10,000 gallons daily; 1 lb per 10,000 gallons to superchlorinate.
• CDC Healthy Swimming — Inflatable and plastic kiddie pools (opens in a new tab) — Empty kiddie pools at least daily; it is unsafe to add chlorine or bromine to them.
• Intex Rainbow Ombre inflatable kiddie pool — product page (opens in a new tab) — 58 in × 13 in; 87 gal at 9 in of wall height.
• Intex My Sea Friends inflatable kiddie pool — product page (opens in a new tab) — 64 × 42 × 18 in; 61 gal at 11 in of wall height.
• Intex Tropical Swim Center family pool — product page (opens in a new tab) — 90 × 60 × 19 in; 159 gal at 13 in of wall height.
• HASA — Hasachlor sodium hypochlorite SDS (2026) (opens in a new tab) — Pool liquid chlorine: sodium hypochlorite 12.5% by weight, about 1.2 g/ml.
• Hill Brothers — Sodium hypochlorite 12.5% specifications (opens in a new tab) — 12.5% by weight = 142 g/L available chlorine (14.2 trade percent), 11.9% available chlorine by weight.
• Pool Essentials chlorinating liquid (retail listing) (opens in a new tab) — A 10% sodium hypochlorite pool chlorine.
• CloroxPro — Germicidal Bleach (retail listing) (opens in a new tab) — A concentrated household-type bleach at 8.25%.
• Clorox Regular Bleach SDS (2020) (opens in a new tab) — Household bleach: sodium hypochlorite 5–10% by weight.
• Langelier saturation index — formula summary (citing Langelier, J. AWWA 28(10):1500–1521, 1936) (opens in a new tab) — pHs = (9.3 + A + B) − (C + D) with A = (log TDS − 1) ÷ 10, B = −13.12 log(°C + 273) + 34.55, C = log(Ca as CaCO₃) − 0.4, D = log(alkalinity as CaCO₃).
• Taylor Technologies — Water Balance (publication 6026) (opens in a new tab) — “Ideally balanced” at 0; “balanced” from −0.3 to +0.5.
• Orenda — The Langelier Saturation Index (factor-table version) (opens in a new tab) — pH + temperature factor + calcium factor + alkalinity factor (corrected for CYA) − TDS factor; CYA correction exactly one-third at pH 7.6.
• Penn State Extension — Corrosive water problems (opens in a new tab) — Negative saturation index values indicate corrosive water; positive values, non-corrosive (scale-forming) water.
• INEOS — Hydrochloric acid 20° Bé product sheet (opens in a new tab) — 20° Baumé hydrochloric acid is 31.45–32.56% HCl, specific gravity about 1.16.
• HASA / Orenda — Muriatic acid product page (opens in a new tab) — 31.45% hydrogen chloride; label limit of one quart per 20,000 gallons per 24 hours to reduce pH.
• HASA — Acid 15 SDS (opens in a new tab) — A lower-strength pool acid: 14.5% hydrochloric acid, specific gravity 1.072.
• Leslie’s — Muriatic acid (label directions) (opens in a new tab) — “Never add more than 16 oz per 10,000 gallons at one time.”
• ProPools / Alliance — pH Down (sodium bisulfate) label (opens in a new tab) — Sodium bisulfate 93.2%; dose chart by pH; never more than 1.5 lb per 10,000 gallons at one time.
• Leslie’s — Dry Acid pH Down (opens in a new tab) — 2 lb lowers total alkalinity by 10 ppm in 10,000 gallons; 15 oz for pH 7.6–7.8, 20 oz for 7.8–8.0.
• US EPA label 1258-161 — HTH calcium hypochlorite 73% (opens in a new tab) — Calcium hypochlorite 73% (70% minimum available chlorine); a 1 lb bag shock-treats 15,000 gallons.
• US EPA — Introduction to pesticide labels (opens in a new tab) — Pool sanitizers are registered pesticides; the label is the law.
• US DOE Energy Saver — Choosing, installing and operating an efficient swimming pool pump (archived) (opens in a new tab) — Start at 6 hours of filtration a day; fewer hours and a smaller pump cut pumping energy by up to 75% in DOE’s Florida example.
• US DOE Energy Saver — Swimming pool covers (archived) (opens in a new tab) — Covers cut heating costs 50%–70%, make-up water 30%–50% and chemicals 35%–60%; evaporation is by far the largest energy loss.
• ENERGY STAR — Pool pumps (opens in a new tab) — Halving pump speed uses one-eighth as much energy; certified in-ground pumps use 20% less energy than standard models.
• US EIA — British thermal units (Btu) (opens in a new tab) — 1 therm of natural gas = 100,000 Btu; 1 gallon of propane ≈ 91,452 Btu; 1 kWh = 3,412 Btu.
• Southern Nevada Water Authority — Pools and spas (opens in a new tab) — In Las Vegas the average in-ground pool loses 48.6 gallons per square foot a year to evaporation; covers reduce evaporation by 90%.
• CDC — Fecal incident response recommendations for aquatic staff (opens in a new tab) — Formed stool: 2 ppm for 25–30 min at pH ≤ 7.5. Diarrhea: CT 15,300 (20 ppm for 12.75 h); with CYA lowered to 15 ppm or less, 20 ppm for 28 h, 30 ppm for 18 h or 40 ppm for 8.5 h.
• Southern Nevada Water Authority — Water leaks (opens in a new tab) — Bucket test to tell evaporation from a pool leak.
• US EPA WaterSense — Pool water efficiency (opens in a new tab) — Using a pool cover can prevent up to 95 percent of pool water evaporation.
• Hayward ProSeries high-rate sand filter manual (IS210TS Rev A) (opens in a new tab) — Filter area and pounds of sand for S144T to S360T2; sand 0.45–0.55 mm, “No. 20 Silica Pool”; cap the internal pipe, fill the tank about half with water, keep sand at least 10 in below the top; backwash at 8–10 psi over clean pressure.
• Hayward — ProSeries 16 in sand filter (S166T) product page (opens in a new tab) — “This filter requires 100 lbs of #20 silica pool filter sand”; in its Q&A Hayward recommends only filter sand in its filters.
• Hayward ProSeries sand filter brochure (2011) (opens in a new tab) — Design flows based on 20 gpm per sq ft: S180T 35, S210T 44, S220T 52, S244T 62, S270T 74 gpm.
• Hayward ProSeries above-ground sand filter sell sheet (2025) (opens in a new tab) — Design flows S144T 25 and S166T 30 gpm.
• Pentair Triton II sand filter brochure (opens in a new tab) — Filter area, tank diameter, pounds of standard #20 silica sand and design flow for TR40 to TR140.
• Pentair Sand Dollar sand filter brochure (2020) (opens in a new tab) — Filter area, pounds of sand and flow for SD35 to SD80. An older (2014) brochure lists 200 lb for the SD60.
• Intex — Krystal Clear sand filter pumps (product pages for SX1500, SX2100, SX2800, SX3000) (opens in a new tab) — Tank size, #20 silica sand capacity, glass media capacity, system flow rate and maximum pool size for each model.
• US DOE Energy Saver — Gas swimming pool heaters (archived) (opens in a new tab) — Sizing: pool area × temperature rise × 12, based on a 1° to 1-1/4°F rise per hour and a 3-1/2 mph average wind; ×1.5 for a 1-1/2°F rise, ×2 for 2°F. Gas heaters from 75,000 to 450,000 Btu; some reach 89%–95% efficiency.
• US DOE Energy Saver — Heat pump swimming pool heaters (archived) (opens in a new tab) — COPs usually 3.0 to 7.0, rated at 80°F air, 63% humidity and 80°F water; efficient above about 45–50°F outside; standard sizes 3.5 hp/75,000 Btu, 5 hp/100,000 Btu and 6 hp/125,000 Btu; same ×12 sizing formula.
• US DOE Energy Saver — Managing swimming pool temperature (archived) (opens in a new tab) — Typical setting 78–82°F; each degree warmer costs 10%–30% more energy.
• Pentair — Pump affinity laws and energy savings (opens in a new tab) — Flow ∝ speed, head ∝ speed², power ∝ speed³; halving speed cuts consumption by 87%.
• US DOE Building America — Measure guideline: replacing single-speed pool pumps with variable-speed pumps (Hunt & Easley, 2012) (opens in a new tab) — One pump measured at 3,450 rpm 2,000 W, 1,800 rpm 250 W, 1,200 rpm 74 W. Worked example: a 25,000 gallon pool at 12.6 kWh a day on a single-speed pump vs 2.2 kWh a day for a variable-speed pump at 22 gpm, 116 W, 19 hours.
• Hayward — AquaRite salt chlorination owner’s manual (092538 Rev D) (opens in a new tab) — “The ideal salt level is between 2700-3400 ppm … with 3200 ppm being optimal”; salt usually comes in 40–80 lb bags.
• Hayward — AquaRite S3 manual (1011728 Rev B) (opens in a new tab) — Operating range 1,200–8,000 ppm with 3,200 ppm optimal; default low/high salt alarms at 2,700 and 3,400 ppm.
• Pentair — IntelliChlor Plus / LT owner’s manual (opens in a new tab) — Ideal 3,600 ppm, 2,600–4,500 ppm range; from 0 ppm, 300 lb (136 kg) of salt per 10,000 gallons reaches 3,600 ppm.
• US EPA label 82289-2 — sodium hypochlorite pool chlorine (opens in a new tab) — Superchlorinate to 5–10 ppm; no pool re-entry above 4 ppm chlorine.
• US EPA — Use of the term “shock” on pool and spa products (opens in a new tab) — “Shock” is a pesticide claim; shock products must be registered and used as labelled.
• Leslie’s — Pool Stabilizer (cyanuric acid) label (opens in a new tab) — 100% cyanuric acid; 2-1/2 lb per 10,000 gallons raises CYA by 30 ppm.
• Leslie’s — Instant Pool Water Conditioner Plus (liquid) label (opens in a new tab) — 4 oz in 10,000 gallons raises CYA 1 ppm; 1 gallon raises it 32 ppm per 10,000 gallons.
• ProPools / Alliance — pH Up (sodium carbonate) label (opens in a new tab) — Sodium carbonate 100%; a maximum of 1 lb per 10,000 gallons per addition.
• Haviland — pH Up label (Poolweb) (opens in a new tab) — pH 6.8–7.1: 1 lb per 10,000 gallons; below 6.8: 1.5 lb.
• Leslie’s — Soda Ash pH Up (opens in a new tab) — Below pH 7.2, 1 lb per 10,000 gallons; no more than 4 lb per 10,000 gallons at a time.
• Intex — 18 ft solar pool cover (opens in a new tab) — Round covers are sold by the pool’s nominal size: this one is designed for 18 ft diameter pools.
• Swimline — liners and covers catalog (opens in a new tab) — Winter covers are sized with a full 4 ft overlap for above-ground pools and 5 ft for inground; solar covers float on the water instead.
• CDC Healthy Swimming — Pool chemical safety toolkit (opens in a new tab) — Store pool chemicals below 95°F (35°C).
• CDC MMWR — Pool chemical–associated health events (2019) (opens in a new tab) — An estimated 3,000–5,000 emergency department visits a year from pool chemical injuries.
• Bestway SaluSpa AirJet 2–4 person inflatable hot tub (opens in a new tab) — 71 in × 26 in outside, 52 in inside, 177 gallons.
• Lay-Z-Spa Rome AirJet (opens in a new tab) — 180 cm outside, 130 cm inside, 840 L.
• Lay-Z-Spa Copenhagen AirJet (opens in a new tab) — 190 cm, 1,300 L.
• Poison Control (National Capital Poison Center) (opens in a new tab) — The US Poison Help line is 1-800-222-1222.
• US DOE Energy Saver — Solar swimming pool heaters (archived) (opens in a new tab) — Collector area typically 50%–100% of the pool’s surface area.
• Hot tub manufacturers’ spec pages (Hot Spring, Caldera, Bullfrog, Jacuzzi, Cal Spas) (opens in a new tab) — Published capacities and outside sizes behind the hot tub gallons estimate; each model is linked on that calculator.

How the site is funded

Easy Pool Calc is free and has no sign-up. It is supported by display advertising and by affiliate links — when you buy something through a product link we may earn a small commission at no extra cost to you. Recommendations are chosen for fit with the job, not commission.

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