Langelier Saturation Index Calculator
Calculate the Langelier Saturation Index from pH, temperature, calcium, alkalinity and CYA using the published factor tables.
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What this tool does
Calculate the Langelier Saturation Index from pH, temperature, calcium, alkalinity and CYA using the published factor tables. Factor tables are the standard published LSI tables (temperature factors interpolated between table points; calcium and alkalinity factors in their logarithmic table form). LSI addresses calcium-carbonate saturation only.
How to use the Langelier Saturation Index Calculator
- Enter or select ph.
- Enter or select water temperature (°f).
- Enter or select calcium hardness (ppm).
- Enter or select total alkalinity (ppm).
- Enter or select cyanuric acid / stabilizer (ppm).
- Enter or select pool type (tds factor).
- Read the calculated result; change any measurement to compare alternatives.
Formula
LSI = pH + TF(temp table) + CF(log10 Ca − 0.4) + AF(log10 corrected alkalinity) − TDS factor; corrected alkalinity = TA − CYA ÷ 3
- ph
- pH
- temp
- Water temperature (°F)
- calcium
- Calcium hardness (ppm)
- alkalinity
- Total alkalinity (ppm)
- cya
- Cyanuric acid / stabilizer (ppm)
- poolType
- Pool type (TDS factor)
Factor tables are the standard published LSI tables (temperature factors interpolated between table points; calcium and alkalinity factors in their logarithmic table form). LSI addresses calcium-carbonate saturation only.
Worked example
For langelier saturation index calculator, the following measurements illustrate the exact method: pH: 7.5; Water temperature (°F): 84; Calcium hardness (ppm): 300; Total alkalinity (ppm): 100; Cyanuric acid / stabilizer (ppm): 30; Pool type (TDS factor): fresh.
Inputs
- pH7.5
- Water temperature (°F)84
- Calcium hardness (ppm)300
- Total alkalinity (ppm)100
- Cyanuric acid / stabilizer (ppm)30
- Pool type (TDS factor)Fresh water — TDS factor 12.1
Result
- Langelier Saturation Index (LSI)0.13
- Water tendencyBalanced range
- Temperature factor0.7
- Calcium factor2.08
- Alkalinity factor (CYA-corrected)1.95
- CYA-corrected alkalinity (ppm)90
Results explained
- Langelier Saturation Index (LSI)
- Langelier Saturation Index (LSI) from the formula above. Factor tables are the standard published LSI tables (temperature factors interpolated between table points; calcium and alkalinity factors in their logarithmic table form). LSI addresses calcium-carbonate saturation only.
- Water tendency
- Water tendency from the formula above. Factor tables are the standard published LSI tables (temperature factors interpolated between table points; calcium and alkalinity factors in their logarithmic table form). LSI addresses calcium-carbonate saturation only.
- Temperature factor
- Temperature factor from the formula above. Factor tables are the standard published LSI tables (temperature factors interpolated between table points; calcium and alkalinity factors in their logarithmic table form). LSI addresses calcium-carbonate saturation only.
- Calcium factor
- Calcium factor from the formula above. Factor tables are the standard published LSI tables (temperature factors interpolated between table points; calcium and alkalinity factors in their logarithmic table form). LSI addresses calcium-carbonate saturation only.
- Alkalinity factor (CYA-corrected)
- Alkalinity factor (CYA-corrected) from the formula above. Factor tables are the standard published LSI tables (temperature factors interpolated between table points; calcium and alkalinity factors in their logarithmic table form). LSI addresses calcium-carbonate saturation only.
- CYA-corrected alkalinity (ppm)
- CYA-corrected alkalinity (ppm) from the formula above. Factor tables are the standard published LSI tables (temperature factors interpolated between table points; calcium and alkalinity factors in their logarithmic table form). LSI addresses calcium-carbonate saturation only.
Frequently asked questions
LSI = pH + temperature factor + calcium factor + alkalinity factor − TDS factor, using the published LSI factor tables: temperature factors run 0.0 at 32 °F to 0.9 at 105 °F, the calcium factor is log₁₀(calcium) − 0.4, and the alkalinity factor is log₁₀(corrected alkalinity).
Cyanuric acid contributes to the total-alkalinity titration but not to carbonate buffering. The standard correction subtracts about one third of the CYA reading from total alkalinity before taking the alkalinity factor.
Roughly −0.3 to +0.3 is considered balanced. Below −0.3 water trends corrosive (etching plaster, attacking metal); above +0.3 it trends scale-forming.
The published table uses 12.1 for fresh water below about 1,000 ppm TDS and 12.2 for salt pools around 3,000–4,000 ppm. This tool selects it from the pool-type input.
No — it is a saturation tendency index for calcium carbonate only. It says nothing about chlorine sanitation, metals staining, or other corrosion mechanisms.