How These Calculators Work
Values on this site were compiled on 2026-10-11. That is the date the figures and formulas were written down, not the date the pages were built.
The value file holds 60 verified figures, 15 standard formulas, and 15 unverified rows. An unverified row has no number. The page says Not verified instead.
How a Result Is Produced
Each calculator page is static HTML. The result next to the inputs is computed from the formula for the inputs shown. When JavaScript is available, editing a field runs the same formula again. Reference tables are computed when the pages are built. Nothing about your location is sent or loaded.
Chemical doses are estimates. They are not a label, and they are not medical or safety advice beyond the warnings printed on the chemical pages. Follow the product label.
CDC figures are marked Source: CDC and include the line that use of CDC information does not imply endorsement by CDC. Extension and manufacturer figures are restated in our words, with the source named on the row. We do not reprint a fact sheet.
Standard Formulas
| Formula | Expression | Note |
|---|---|---|
| Pounds of water per US gallon in the dosing formula | 8.34 | Standard formula. Pounds = gallons × 8.34 × ppm change ÷ 1,000,000 ÷ active fraction. |
| Product amount per 10,000 gallons from the dosing formula | 8.34 × 10000 × ppm change ÷ 1,000,000 ÷ active fraction | Calculated from the standard dosing formula. |
| US gallons per cubic foot | 7.48 | Standard conversion (also used in a CDC MAHC Annex worked example). |
| Rectangular volume | length × width × average depth × 7.48 | Standard formula. |
| Circular volume | 3.14159 × radius^2 × average depth × 7.48 | Standard formula. Pi is 3.14159. About diameter^2 × depth × 5.875. |
| Oval volume | 3.14159 / 4 × length × width × average depth × 7.48 | Standard formula. |
| Average depth | (shallow + deep) / 2 | Standard formula. |
| Flow from volume and turnover | gallons / (hours × 60) | Standard formula (as in a MAHC Annex example). |
| Heat input | gallons × 8.34 × temperature rise F | Standard formula. 1 BTU raises 1 pound of water by 1 F. |
| Heater rate | BTU / hours | Standard formula. |
| Pounds per acre from pounds per 1,000 square feet | 43.56 | Standard conversion. 43,560 square feet per acre. |
| Sod area with waste | area × (1 + waste fraction) | Standard formula. |
| Cubic yards from area and depth | 324 | Standard formula. 27 cubic feet per cubic yard × 12 inches per foot. |
| Cubic yards of mulch or gravel from area and depth | 324 | Standard formula. Same divisor as soil: 27 cubic feet per cubic yard × 12. |
| Bag volume | user enters cubic feet (2 or 3 are package sizes, not a default) | Package size; user input. |
Verified Figures
| Figure | Value | Unit | Attribution |
|---|---|---|---|
| Minimum free chlorine without cyanuric acid | 1.0 | ppm | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §5.7.3.1.1.2.1. No CDC endorsement implied; available free at cdc.gov. |
| Minimum free chlorine with cyanuric acid | 2.0 | ppm | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §5.7.3.1.1.2.2. No CDC endorsement implied; available free at cdc.gov. |
| Maximum free chlorine while open | 10.0 | ppm | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §5.7.3.1.1.5. No CDC endorsement implied; available free at cdc.gov. |
| Home pool free chlorine, CDC home page | 1-4 | ppm | Source: CDC. Use of CDC information does not imply endorsement by CDC; available free at cdc.gov. |
| pH range | 7.0-7.8 | pH | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §5.7.3.4.1. No CDC endorsement implied; available free at cdc.gov. |
| pH band discussed for Langelier balance | 7.2-7.6 | pH | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §Annex 5.7.4. No CDC endorsement implied; available free at cdc.gov. |
| Total alkalinity adjustment range | 60-180 | ppm | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §Annex 5.7.4. No CDC endorsement implied; available free at cdc.gov. |
| Total alkalinity listed by Pentair IntelliChlor | 80-120 | ppm | Per Pentair IntelliChlor user's guide. |
| Calcium hardness for concrete or plaster | 200-400 | ppm | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §Annex 5.7.4.4.3. No CDC endorsement implied; available free at cdc.gov. |
| Calcium hardness for vinyl or fiberglass | 80-200 | ppm | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §Annex 5.7.4. No CDC endorsement implied; available free at cdc.gov. |
| Calcium hardness when water is above 90 F | 100-200 | ppm | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §Annex 5.7.4.4.3. No CDC endorsement implied; available free at cdc.gov. |
| Maximum cyanuric acid | 90 | ppm | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §5.7.3.1.3.2. No CDC endorsement implied; available free at cdc.gov. |
| Cyanuric acid band in the Pentair IntelliChlor guide | 30-50 | ppm | Per Pentair IntelliChlor user's guide (citing APSP). |
| Cyanuric acid to free chlorine ratio at closure | 45:1 | ratio | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §6.6.3.1. No CDC endorsement implied; available free at cdc.gov. |
| Combined chlorine ceiling | 0.4 | ppm | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §Annex 5.7.3. No CDC endorsement implied; available free at cdc.gov. |
| Cyanuric acid added per 1 ppm free chlorine from dichlor | 0.9 | ppm CYA per ppm FC | Per PHTA technical bulletin on dichlor. |
| Hayward AquaRite salt range (best 3200) | 2700-3400; best 3200 | ppm | Per Hayward AquaRite manual. |
| Pentair IntelliChlor IC15-IC60 salt range (ideal 3600) | 3600-4500; ideal 3600 | ppm | Per Pentair IntelliChlor IC15–IC60 user's guide. |
| Breakpoint chlorination multiplier | 10 | times combined chlorine | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §Definitions: Breakpoint Chlorination. No CDC endorsement implied; available free at cdc.gov. |
| Fecal-incident hyperchlorination when cyanuric acid is 15 ppm or less | 20 ppm for 28 h; 30 ppm for 18 h; 40 ppm for 8.5 h | ppm, hours | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §6.5.3.2.1. No CDC endorsement implied; available free at cdc.gov. |
| Calcium hypochlorite 73 percent product, minimum available chlorine | 70 | wt% available Cl | Per EPA-registered label, HTH Granular 73 (EPA Reg. 1258-1239). |
| Dichlor dihydrate available chlorine | 55.0-57.1 | wt% available Cl | Per OxyChem ACL 56 sales specification. |
| Dichlor anhydrous available chlorine | 62 or more | wt% available Cl | Per OxyChem ACL 60 sales specification. |
| Trichlor available chlorine | 90 or more | wt% available Cl | Per OxyChem ACL 90 PLUS sales specification. |
| Trade percent definition | g available chlorine per 100 mL | g/100 mL | Per Olin Sodium Hypochlorite Product Stewardship Manual (Table 2); also OxyChem Sodium Hypochlorite Handbook. |
| Trade percent from weight percent | wt% NaOCl × specific gravity ÷ 1.050 | trade % | Per Olin Sodium Hypochlorite PSM. |
| 12.5 percent by weight sodium hypochlorite as trade percent | 14.1 | trade % | Per Olin Sodium Hypochlorite PSM, Table 2 (theoretical density). |
| 10, 6, and 8 percent by weight as trade percent | 10.9 / 6.2 / 8.5 | trade % | Per Olin Sodium Hypochlorite PSM, Table 2. |
| 5.25 percent by weight sodium hypochlorite as trade percent | 5.37 | trade % | Per OxyChem Sodium Hypochlorite Handbook. |
| Pesticide label ingredients by weight | percentage by weight | w/w | Source: 40 CFR 156.10(g). |
| 12.5 percent liquid chlorine label convention | 12.5, convention not uniform | % (w/w or trade) | Per HASA 12.5% NaOCl SDS (Weight %) and HASA Sani-Clor product page (trade concentration). |
| One gallon of 12.5 percent trade liquid chlorine in 10,000 gallons | 12.5 | ppm per gal per 10k gal | Per HASA Sani-Clor product page. |
| Household bleach example strength | 5.7 | % available Cl | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §Annex example. No CDC endorsement implied; available free at cdc.gov. |
| Hot tub minimum free chlorine | 3.0 | ppm | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §5.7.3.1.1.2.3. No CDC endorsement implied; available free at cdc.gov. |
| Hot tub chlorine level that CDC says to announce | 10 | ppm | Source: CDC. Use of CDC information does not imply endorsement by CDC; available free at cdc.gov. |
| Hot tub bromine range | 4-8 | ppm | Source: CDC. Use of CDC information does not imply endorsement by CDC; available free at cdc.gov. |
| Hot tub pH | 7.0-7.8 | pH | Source: CDC. Use of CDC information does not imply endorsement by CDC; available free at cdc.gov. |
| Cyanuric acid in a hot tub | 0 (not recommended) | ppm | Source: CDC. Use of CDC information does not imply endorsement by CDC; available free at cdc.gov. |
| Hot tub water temperature maximum | 104 | F | Source: CDC. Use of CDC information does not imply endorsement by CDC; available free at cdc.gov. |
| Hot tub calcium hardness above 90 F | 100-200 | ppm | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §Annex 5.7.4.4.3. No CDC endorsement implied; available free at cdc.gov. |
| MAHC maximum turnover for other public pools | 6 | hours | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §Table 4.7.1.10. No CDC endorsement implied; available free at cdc.gov. |
| MAHC turnover for a public hot tub at 93-104 F | 0.5 | hours | Source: CDC, 2023 Model Aquatic Health Code (MAHC), §Table 4.7.1.10. No CDC endorsement implied; available free at cdc.gov. |
| Tall fescue new-lawn seeding rate | 6-8 | lb/1,000 ft2 | Seeding rate: Virginia Cooperative Extension (SPES-299); also Penn State Extension, K-State Research and Extension. |
| Kentucky bluegrass new-lawn seeding rate | 2-3 | lb/1,000 ft2 | Seeding rate: Virginia Cooperative Extension; Penn State Extension. |
| Perennial ryegrass new-lawn seeding rate | 4-5; Virginia Cooperative Extension lists 3-5 | lb/1,000 ft2 | Seeding rate: Penn State Extension; Virginia Cooperative Extension. |
| Bermudagrass new-lawn seeding rate | 1-2 hulled; 5-10 unhulled | lb/1,000 ft2 | Seeding rate: Virginia Cooperative Extension; NC State Extension. |
| Zoysiagrass new-lawn seeding rate | 1-2 | lb/1,000 ft2 | Seeding rate: Virginia Cooperative Extension; NC State Extension. |
| St. Augustinegrass seeding rate | none (sod or plugs) | — | NC State Extension lists no seeding rate (vegetative planting). |
| Overseeding, tall fescue and Kentucky bluegrass | tall fescue 3-4; Kentucky bluegrass 1-1.5 | lb/1,000 ft2 | Overseeding: K-State Research and Extension. |
| Mowing height, cool-season grasses | Kentucky bluegrass and perennial ryegrass 2.5-3.5; tall fescue 3.0-4.0 | inches | Mowing height: Purdue Extension AY-20. |
| Germination, Kentucky bluegrass and tall fescue | Kentucky bluegrass 18-28; tall fescue 14-21 | days | Germination: Purdue Extension AY-20. |
| Product pounds from nitrogen pounds and bag percent | N lb / (N% / 100) | lb product/1,000 ft2 | Method: Rutgers NJAES FS839. |
| Quick-release nitrogen single-application cap | 1 | lb N/1,000 ft2 | Rutgers NJAES FS839. |
| Cool-season fall nitrogen | 1-1.5 | lb N/1,000 ft2 | K-State Research and Extension. |
| Compost topdressing depth | 0.25 | inch | NC State Extension (organic lawn care). |
| Topsoil density | 2430 lb/yd3 (about 1.22 tons/yd3) | lb/yd3 | Source: Delaware DOT Material Average Weight Chart. |
| Organic mulch depth | 2-4; fine mulch 1-2 | inches | Virginia Cooperative Extension SPES-661. |
| No. 57 stone tons per cubic yard | 2781 lb/yd3 (about 1.39 tons/yd3) | lb/yd3 | Source: Delaware DOT Materials and Research, Material Average Weight Chart (2013). |
| No. 8 stone tons per cubic yard | 2646 lb/yd3 (about 1.32 tons/yd3) | lb/yd3 | Source: Delaware DOT Material Average Weight Chart. |
| Chip-seal aggregate tons per cubic yard | 1.4 | tons/yd3 | Source: Nebraska DOT estimating guide (chip seal aggregate). |
Figures We Ask You to Enter
These rows stay empty. The calculators that would have used them ask you to type your own number, or they skip the output.
Lime converts a soil-test rate across your area. It does not choose a rate from pH. Sod divides your area, plus the waste percent you type, by the roll size you type. Topsoil uses the depth you type, then multiplies cubic yards by 1.22 to show tons.
| Item | Status |
|---|---|
| Cyanuric acid added per 1 ppm free chlorine from trichlor | Not verified |
| Generic salt target with no model named | Not verified |
| Routine home shock target | Not verified |
| Calcium hypochlorite 65 percent available chlorine | Not verified |
| Kidney or irregular shape factor | Not verified |
| Home pool turnover default | Not verified |
| Surface heat loss or wind factor | Not verified |
| Overseeding, ryegrass and warm-season grasses | Not verified |
| Warm-season mowing height and germination | Not verified |
| Square feet per roll or pallet | Not verified |
| Default sod waste percent | Not verified |
| Yearly nitrogen total by grass | Not verified |
| Generic lime rate from pH | Not verified |
| Single lime application cap | Not verified |
| Recommended depth for a new lawn | Not verified |
Liquid Strength and Stone Weight
Trade percent is grams of available chlorine per 100 milliliters. It is the default on the chlorine calculator. Weight percent is converted with the Olin table: 12.5 percent by weight is about 14.1 trade percent.
Six percent by weight is about 6.2 trade percent. Household bleach sold as 8.25% is weight percent, about 8.8 trade % (interpolated from the Olin conversion table).
No. 57 stone is 1.39 tons per cubic yard and No. 8 stone is 1.32, from the Delaware DOT chart. Topsoil uses 1.22 tons per cubic yard from the same chart. The 1.4 figure in a Nebraska DOT guide is for chip seal, so we don't use it.