TDS Calculator

Water Chemistry & Electrical Conductivity to TDS Relationships

Total Dissolved Solids (TDS) represents the total concentration of dissolved inorganic salts (calcium, magnesium, potassium, sodium, bicarbonates, chlorides, sulfates) and small amounts of organic matter dissolved in water, measured in parts per million (ppm) or mg/L.

Primary Water Quality Equations

• TDS Conversion Equation: $\text{TDS (ppm)} = EC_{25} \times k_e$

• Temperature Compensation Equation ($25^\circ\text{C}$ Standard):

$$EC_{25} = \frac{EC_T}{1 + 0.0191 \times (T - 25)}$$

• Reverse Osmosis (RO) Membrane Rejection Rate:

$$\text{Rejection \%} = \left(\frac{\text{Feed TDS} - \text{Permeate TDS}}{\text{Feed TDS}}\right) \times 100\%$$

Standard Conversion Multipliers ($k_e$)

• $k = 0.50$: Common in Hanna instruments.

• $k = 0.55$ (Municipal Tap Water Standard): Standard for natural groundwater and urban utilities.

• $k = 0.64$ (442 Natural Water Standard): EPA benchmark for natural river basins.

• $k = 0.70$: Used in commercial greenhouse nutrient monitoring.

WHO / EPA Drinking Water Palatability Scale

• $< 50\text{ ppm}$: Demineralized / Distilled (flat taste).

• $50 - 300\text{ ppm}$: Excellent / Ideal Drinking Quality (crisp, refreshing taste).

• $300 - 600\text{ ppm}$: Good (moderate mineral content).

• $600 - 900\text{ ppm}$: Fair (hard water, slight scale buildup).

• $900 - 1,200\text{ ppm}$: Poor (heavy mineral taste).

• $> 1,200\text{ ppm}$: Unacceptable (exceeds EPA secondary aesthetic limits of 500 ppm).

How to Use This Calculator

Enter Electrical Conductivity, TDS Conversion Factor (k), Water Sample Temperature (°C), Post-RO Filter Permeate TDS (ppm — optional) into the input fields and the calculator will instantly compute Total Dissolved Solids (TDS), Temperature-Compensated EC (25°C). All calculations happen in real time — no submission or page reload required. You can adjust any input value and see the result update immediately.

Understanding Your Result

The TDS result gives you a precise, calculated value based on the inputs you provide. Compare your result against published benchmarks from NIST and ISO international standards to assess where you stand. A single calculation is a useful starting point, but tracking this metric over time — as inputs change — gives you a much more complete picture.

Practical Application

The TDS is most useful when you have specific, real-world data to enter. For example: enter your actual Electrical Conductivity to calculate your total dissolved solids (tds). The result helps students, engineers, scientists, and educators make informed decisions about solving mathematical problems, verifying calculations, and teaching concepts. This calculator is trusted by professionals and individuals alike because it follows the exact formulas validated by NIST and ISO international standards.

Accuracy Notes and Limitations

Results are based on exact mathematical definitions. Verify that formula assumptions match your specific use case. The accuracy of any calculator is limited by the quality of the inputs provided. Double-check your units before entering values — unit errors are the most common source of incorrect results. For critical decisions, cross-reference with at least one additional source or professional consultation.

Frequently Used With

This calculator is often used alongside other math tools to build a complete analytical picture. Combining multiple related calculations provides stronger evidence for decisions than relying on any single metric. Browse the Math category to find complementary calculators for your specific use case.