Total dissolved solids (TDS) calculator
Estimate water TDS from a laboratory ion analysis or from electrical conductivity at 25 °C.
Inputs
Anions (mg/L)
Cations (mg/L)
Live results
Anions and cations summary
328.00 mg/L (80.79%)
78.00 mg/L (19.21%)
Calculation breakdown
| Component | Group | Concentration | Share of TDS |
|---|
How to use this TDS calculator
What this calculator does
This calculator estimates total dissolved solids in water by either adding the measured concentrations of common dissolved anions and cations or multiplying electrical conductivity by a user-selected conversion factor. It is useful for reviewing a laboratory water report, checking a field-meter reading, comparing source waters, or preparing a quick treatment or monitoring worksheet. It does not identify every dissolved compound, confirm potability, replace a certified laboratory analysis, or account for neutral dissolved substances that do not contribute strongly to conductivity.
When to use it
Use the water-analysis method when your report lists individual ion concentrations in mg/L. Use the electrical-conductivity method when you have an EC reading but no complete ion panel. It is also useful for screening changes over time, checking whether two reports are broadly consistent, and creating a documented Excel record for quality-control notes.
How to calculate
- The calculator opens with a complete demonstration water analysis and an immediately available example XLSX file.
- Select Calculation method. For Water analysis, replace any applicable ion values and leave absent ions at zero. For Electrical conductivity, enter the Conversion factor (k) and Electrical conductivity (EC).
- Read Total dissolved solids (TDS), the group totals, equivalent ppm, water class, chart, and breakdown table. Results update live.
- Select Download Excel to export the current validated model. Reset clears the demonstration and calculated content; export remains disabled until a complete valid state is entered again.
Input guide
Calculation method is required and selects the formula path. In water-analysis mode, every ion field accepts a nonnegative decimal concentration in mg/L using a period as the decimal separator; scientific notation and decimal commas are rejected. The anion fields are Chloride (Cl⁻), Phosphate (H₂PO₄⁻), Sulfite (SO₃²⁻), Sulfate (SO₄²⁻), Carbonate (CO₃²⁻), Bicarbonate (HCO₃⁻), Fluoride (F⁻), Nitrite (NO₂⁻), Nitrate (NO₃⁻), and Silicate (SiO₄⁴⁻). The cation fields are Sodium (Na⁺), Calcium (Ca²⁺), Magnesium (Mg²⁺), Iron (Fe²⁺), Barium (Ba²⁺), Potassium (K⁺), Strontium (Sr²⁺), Manganese (Mn²⁺), Aluminium (Al³⁺), and Lithium (Li⁺). A realistic entry might be 85 mg/L chloride or 24 mg/L calcium. Increasing any valid ion concentration increases TDS by the same number of mg/L. Do not enter milliequivalents per liter, molarity, hardness as CaCO₃, or a negative value into these fields.
In conductivity mode, Conversion factor (k) is a required unitless decimal from 0.50 to 0.80; 0.67 is a practical general estimate when a calibrated site-specific factor is unavailable. Electrical conductivity (EC) is a required nonnegative value in µS/cm, preferably measured or corrected to 25 °C. A value of 606 µS/cm with k = 0.67 gives about 406.02 mg/L. The relationship is empirical, so changing k changes the estimate proportionally. The U.S. Environmental Protection Agency explains the role of conductivity as an indicator of dissolved ions.
Output guide
Total dissolved solids (TDS) is the primary result in mg/L. Anions total and Cations total are exact group sums in water-analysis mode and are not separately available from a conductivity-only estimate. Equivalent ppm uses the common water approximation that 1 mg/L is numerically about 1 ppm when density is near 1 kg/L. Water class places the value into freshwater (<1,000 mg/L), brackish (1,000 – 10,000 mg/L), saline (10,000 – 35,000 mg/L), or hypersaline (>35,000 mg/L) screening bands. The chart compares the two compatible ion-group totals, while the table lists each nonzero component, its group, concentration, and share of TDS. These are calculations and classifications, not a safety recommendation; zero means no entered or estimated dissolved solids, while unusually high values should be confirmed with appropriate sampling and laboratory methods.
Worked example
The startup analysis contains 328.00 mg/L of anions and 78.00 mg/L of cations. The calculator applies the identity TDS = Σ anions + Σ cations, so 328.00 + 78.00 = 406.00 mg/L. For water of approximately unit density, this is also displayed as 406.00 ppm. Because 406 mg/L is below 1,000 mg/L, the screening class is freshwater. The chart shows roughly 80.79% anions and 19.21% cations, and the workbook stores the typed inputs and full result breakdown rather than rounded screen text.
Learn more
The U.S. Geological Survey overview of salinity and dissolved salts explains why mineral content matters in natural waters. For drinking-water context, review the EPA's secondary drinking-water standards guidance, where TDS is treated mainly as an aesthetic parameter. Laboratory gravimetric practice is described in the EPA Method 160.1 document for filterable residue.
Formula and interpretation
For a complete chemistry panel, the model simply sums the reported mass concentrations. For conductivity, the model uses TDS = k × EC. The factor varies because ions differ in charge, mobility, and composition, and because conductivity is temperature-sensitive. A site-specific factor established from paired laboratory TDS and EC measurements is stronger than a generic factor. TDS alone cannot distinguish beneficial minerals from undesirable contaminants, and two waters with the same TDS may have very different chemistry.
Common mistakes
Do not mix mg/L with mEq/L, confuse conductivity in mS/cm with µS/cm, or use an EC reading that has not been temperature compensated when the meter requires it. One mS/cm equals 1,000 µS/cm. Avoid double-counting totals already supplied by a laboratory, and remember that the conductivity method is an approximation. For compliance or health decisions, use the applicable jurisdiction's sampling, analytical, and reporting requirements.