Salinity (EC) Calculator
Enter the electrical conductivity (EC) of soil or irrigation water and a conversion factor; the tool instantly estimates total dissolved solids TDS (mg/L = ppm) and salt content (g/L) to assess water quality and salt-stress risk.
Input Data
Results
At a glance:Estimating salinity from EC is a practical way to convert a solution's conductivity into dissolved-salt concentration. Salt dissolved in water or soil solution dissociates into charged ions (Na⁺, Cl⁻, Ca²⁺, SO₄²⁻, etc.); more ions and higher concentration mean better conductivity, so electrical conductivity (EC, commonly dS/m = mS/cm) serves as a proxy for total salt. Empirically, total dissolved solids TDS is approximately proportional to EC: TDS(mg/L) = EC(dS/m) × factor. The factor is not a fixed constant — it varies with the salt composition and concentration (different ions have different equivalent conductivities; at higher concentration ionic interactions grow stronger), generally between 550 and 800; horticulture, agriculture and fresh water commonly use 640 (1 dS/m ≈ 640 mg/L), while NaCl-dominated high-sodium or seawater can use about 700. TDS in mg/L equals ppm numerically in dilute solution, and dividing by 1000 gives g/L. The significance of salinity: the higher the EC/TDS, the greater the osmotic pressure of the solution, the harder for roots to take up water — crops may show 'physiological drought' and growth inhibition even when soil is wet, and excess ions (Na, Cl, B) can cause specific toxicity or destroy soil structure. Therefore the EC of irrigation water and the soil saturation-extract EC (ECe) are core water-quality parameters for assessing salt-stress risk, choosing salt-tolerant crops and planning leaching. When using this calculator: EC should be temperature-corrected (usually standardized to 25 °C); for soil, state whether it is saturation extract or a fixed soil:water ratio leachate; and choose the factor by local water quality for reliable TDS.
Formula
Total dissolved solids: TDS(mg/L) = EC(dS/m) × factor.
Salt content: TDS(g/L) = TDS(mg/L) ÷ 1000.
Units: 1 dS/m = 1 mS/cm; mg/L ≈ ppm in dilute solution.
$$TDS_{mg/L} = EC_{dS/m} \times k$$$$TDS_{g/L} = \dfrac{TDS_{mg/L}}{1000}$$How to Use
- Measure the solution EC (irrigation water or soil extract) with a conductometer, confirmed at 25 °C temperature correction.
- Choose the conversion factor by water quality (horticulture/fresh water commonly 640, high-sodium water about 700).
- Enter EC and the factor; the tool instantly gives TDS(mg/L=ppm) and salt content(g/L); higher values mean more salt and greater stress risk.
General irrigation-water / soil-solution salinity classes (relative, varies by crop salt tolerance)
| EC (dS/m) | TDS≈(mg/L, k=640) | Salinity Level & Impact |
|---|---|---|
| < 0.7 | < 450 | No salinity limit; suitable for most crops |
| 0.7 – 2.0 | 450 – 1280 | Mild; sensitive crops may be affected |
| 2.0 – 4.0 | 1280 – 2560 | Moderate; choose tolerant varieties or increase leaching |
| > 4.0 | > 2560 | Severe; most crops show clear yield loss |
Classes follow FAO irrigation-water guidelines; actual thresholds depend on crop tolerance, soil and leaching management. TDS by chosen factor.
Case Studies
Estimate irrigation-water TDS from EC
An irrigation water reads EC = 2 dS/m; use the common factor 640.
TDS = 2 × 640 = 1280 mg/L (1280 ppm), salt content = 1280 ÷ 1000 = 1.28 g/L.
Light-to-moderate salinity; sensitive crops need attention, consider mixing with purer water to dilute.
High-sodium source with larger factor
NaCl-dominated source EC = 3 dS/m, factor 700.
TDS = 3 × 700 = 2100 mg/L (2.1 g/L).
Reached moderate salinity; long-term irrigation must monitor soil ECe accumulation and plan leaching to avoid salt build-up hurting roots.
FAQ
Why isn't the conversion factor fixed, and what should I use?
The factor reflects 'how much dissolved solid per unit conductivity'; different salts' ion equivalent conductivities differ and interactions grow with concentration, so the factor varies, generally 550–800. Horticulture, agriculture and fresh water most commonly use 640 (1 dS/m ≈ 640 mg/L); NaCl-dominated high-sodium or coastal sources about 700. If you have lab evaporation-residue (true TDS) vs EC data, best use your own regression factor.
How do dS/m, mS/cm, µS/cm convert?
1 dS/m = 1 mS/cm = 1000 µS/cm. Agriculture and soil use dS/m; home meters often show µS/cm or ppm. If the reading is µS/cm, divide by 1000 to dS/m then multiply by the factor; if the instrument gives ppm directly it has already applied a factor (often 500 or 700) — check to avoid double conversion.
Is TDS(mg/L) the same as ppm?
In dilute aqueous solution, mg/L and ppm are numerically equal (1 L water ≈ 1 kg, mg/kg = ppm). Very concentrated or density-far-from-1 solutions differ slightly, but within normal agriculture/horticulture they are interchangeable. This calculator's mg/L output equals ppm.
How does high EC/TDS affect crops?
More salt means higher solution osmotic pressure, harder for roots to take up water — crops may show physiological drought, wilting, slower growth and yield loss even when soil is wet; excess Na, Cl, B can cause specific toxicity (leaf-margin scorch), and high sodium destroys soil structure and permeability. Crop tolerance thresholds vary widely; manage by variety choice, leaching and dilution.
What to watch when measuring EC?
EC is temperature-sensitive; readings are usually standardized to 25 °C (most meters auto-compensate); calibrate and clean electrodes with standards regularly. For soil, state the method — saturation-paste extract (ECe, the agricultural standard) or fixed ratios like 1:2, 1:5 leachate; the numbers are not directly comparable. Sample representatively and record depth and time.
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References
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.