Science & Lab Tools
TDS Calculator
Calculate Total Dissolved Solids (TDS) from conductivity measurements in water samples
Reviewed by the calculator.uk.com Team · Last reviewed 8 May 2026 · Our methodology
Enter conductivity values to calculate TDS
Related to TDS Calculator
The TDS (Total Dissolved Solids) calculator converts electrical conductivity (EC) measurements into TDS values, which represent the total concentration of dissolved substances in water. The calculation uses the relationship between electrical conductivity and the presence of dissolved ions in the water sample.
The Basic Formula
TDS (ppm) = EC (µS/cm) × TDS coefficient
The TDS coefficient (conversion factor) typically ranges from 0.4 to 1.0, depending on the ionic composition of the water. The most commonly used value is 0.67, which works well for most natural water sources. Different types of water may require different coefficients - for example, water high in sulfates might use a coefficient closer to 0.8, while water high in carbonates might use a lower coefficient.
The TDS value is expressed in parts per million (ppm) or milligrams per liter (mg/L), which are equivalent units. Understanding your TDS results is crucial for various applications in water quality assessment, aquaculture, agriculture, and laboratory analysis.
Common TDS Ranges
- • Fresh drinking water: <500 ppm
- • Brackish water: 1,000-10,000 ppm
- • Saline water: 10,000-35,000 ppm
- • Seawater: ~35,000 ppm
The calculator handles both microsiemens per centimeter (µS/cm) and millisiemens per centimeter (mS/cm) units for electrical conductivity. When using mS/cm, the calculator automatically converts the values to µS/cm before calculating TDS, as this is the standard unit used in the formula.
1. What is TDS and why is it important?
Total Dissolved Solids (TDS) represents the total concentration of dissolved substances in water, including minerals, salts, metals, and ions. It's important for assessing water quality, as it affects taste, water treatment processes, and suitability for various applications like agriculture, aquaculture, and industrial processes.
2. How accurate is the TDS calculation from conductivity?
The accuracy depends on the water composition and the chosen TDS coefficient. The standard 0.67 coefficient provides a good approximation for most natural waters, but accuracy can vary by ±10% depending on the specific ionic composition of the water sample.
3. Why does the TDS coefficient vary?
The TDS coefficient varies because different dissolved ions contribute differently to electrical conductivity. Waters with different ionic compositions (such as sulfates vs. carbonates) require different coefficients for accurate TDS estimation. The coefficient range of 0.4 to 1.0 covers most water types encountered in practice.
4. Can this calculator be used for all water types?
Yes, this calculator can be used for most water types, including drinking water, process water, wastewater, and natural water bodies. However, for extremely high TDS waters (>100,000 ppm) or waters with unusual ionic compositions, direct TDS measurement methods might be more appropriate than conductivity-based calculations.
5. What is the scientific source for this calculator?
This calculator estimates TDS from conductivity using the standard empirical relationship TDS (ppm) ≈ EC (µS/cm) × k, where k typically ranges from 0.4 to 1.0 depending on the water's ionic makeup; a default of 0.67 is a commonly used approximation for many natural waters, consistent with Standard Methods for the Examination of Water and Wastewater (APHA, AWWA, WEF). Because the true ratio is water-specific, direct gravimetric TDS measurement remains more accurate than any conductivity-based estimate.