Free TDS Calculator
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Cations (+)
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Total Dissolved Solids and Water Quality Assessment
The Total Dissolved Solids (TDS) Calculator provides a quick, reliable way to estimate the concentration of dissolved ions in water. It supports two common approaches: entering data from a full water chemistry analysis or converting an electrical conductivity (EC) reading into TDS. This makes it a versatile tool for evaluating drinking water taste, salinity levels, and overall water quality.
Defining Total Dissolved Solids
Total Dissolved Solids (TDS) represents the combined mass of all inorganic and organic particles smaller than 2 µm that are suspended in a water sample. The major contributors are typically the ions responsible for salinity, hardness, and alkalinity. TDS is expressed either in parts per million (ppm), a mass‑per‑mass ratio, or in milligrams per liter (mg/L), a mass‑per‑volume concentration. Because the density of freshwater is approximately 1 kg/L (1000 kg/m³), these two units are numerically interchangeable for most practical purposes.
Common Ions That Contribute to TDS
A standard water analysis report lists the concentrations of various anions and cations. The table below shows the most frequently encountered species and their molar masses.
| Anions | Molar mass (g/mol) | Cations | Molar mass (g/mol) |
|---|---|---|---|
| Cl⁻ | 35.5 | Na⁺ | 23.0 |
| H₂PO₄⁻ | 97.0 | Ca²⁺ | 40.1 |
| SO₃²⁻ | 80.1 | Mg²⁺ | 24.3 |
| SO₄²⁻ | 96.1 | Fe²⁺ | 55.8 |
| CO₃²⁻ | 60.0 | Ba²⁺ | 137.3 |
| HCO₃⁻ | 61.0 | K⁺ | 39.1 |
| F⁻ | 19.0 | Sr²⁺ | 87.6 |
| NO₂⁻ | 46.0 | Mn²⁺ | 54.9 |
| NO₃⁻ | 62.0 | Al³⁺ | 27.0 |
| SiO₄⁴⁻ | 92.1 | Li⁺ | 6.9 |
TDS and Drinking Water Standards
TDS directly affects the taste of tap water. Most guidelines consider a range of 500–1000 mg/L as acceptable for drinking. Water below this level is often described as low‑mineral; values above 1000 mg/L can impart an unpleasant flavor and may signal potential safety concerns. Based on salinity, water bodies are classified as follows:
| Classification | TDS (mg/L) |
|---|---|
| Freshwater | < 1,000 |
| Brackish water | 1,000 – 10,000 |
| Saline water | 10,000 – 35,000 |
| Hypersaline | > 35,000 |
Estimating TDS from a Water Chemistry Report
If a complete ion breakdown is available, TDS can be obtained by summing the concentrations of all measured cations and all measured anions:
Only the ions actually present in the report should be included. The calculator automates this addition and can display a separate cation‑anion balance in milliequivalents per liter (mEq/L).
Converting Electrical Conductivity to TDS
Electrical conductivity (EC) provides an indirect but rapid estimate of TDS. The relationship is linear and depends on a conversion factor:
where:
- EC is the electrical conductivity measured at 25 °C in microsiemens per centimeter.
- is a multiplier that typically ranges from 0.5 to 0.8. When the exact factor is unknown, 0.67 is a widely accepted default.
Because EC‑based TDS only captures ions that carry an electrical charge, non‑conductive solids are not reflected in the result.
How the TDS Calculator Works
The tool offers two calculation modes:
- Water analysis mode: Enter the concentrations of the relevant anions and cations from your laboratory report. The calculator sums them to produce the total TDS value.
- Electrical conductivity mode: Provide the EC reading and, optionally, the conversion factor . The calculator applies the linear formula to estimate TDS.
In both modes, the result is displayed in mg/L (equivalent to ppm). You can also view a summary of the ionic composition and check the charge balance when using the water analysis option.
FAQ
1. How do I convert EC to TDS using the calculator?
Enter the electrical conductivity (µS/cm) measured at 25 °C and, if known, the conversion factor kₑ (default 0.67). The calculator applies TDS = kₑ × EC to give the result in mg/L (equivalent to ppm).
2. Are mg/L and ppm the same for TDS in water?
Yes, for freshwater they are numerically identical because the density of water is approximately 1 kg/L (1000 kg/m³). A value of 500 mg/L is therefore the same as 500 ppm.
3. What is the recommended TDS level for drinking water?
Most guidelines set acceptable TDS levels between 500 and 1000 mg/L. Water below this range is low‑mineral, while levels above 1000 mg/L can affect taste and may indicate quality concerns.
4. How do I calculate TDS from a full water chemistry analysis?
Sum the concentrations (in mg/L) of all cations listed in the report, then sum all anions. Add the two totals: TDS = total cations + total anions. The calculator does this automatically and can also show the anion‑cation balance.
5. Why does the EC‑to‑TDS conversion factor kₑ vary between 0.5 and 0.8?
The factor depends on the ionic composition and the concentration of dissolved solids. A higher kₑ corresponds to a higher conductivity per unit TDS. When the exact factor is unknown, 0.67 is a reliable approximation.
How to Use
- Select the calculation method: Water analysis or Electrical conductivity.
- For water analysis, enter the concentrations of anions and cations from your water report.
- For electrical conductivity, enter the conversion factor k and the EC value. Click Calculate.