TDS Calculator

Total Dissolved Solids (TDS) represent the combined mass of all inorganic and organic substances dissolved in a liquid, typically measured in milligrams per liter (mg/L) or parts per million (ppm). When evaluating water chemistry via ion chromatography, TDS is calculated by summing the individual mass concentrations of all major anions (like chloride, sulfate, and bicarbonate) and cations (like sodium, calcium, and magnesium). Alternatively, TDS can be estimated rapidly through electrical conductivity (EC) using the empirical formula ${\mathrm{TDS}}_{\mathrm{elec}}=k\times \mathrm{EC}$, where $k$ is a conversion factor usually ranging between 0.55 and 0.80 depending on the ionic makeup of the solution.

Imagine you are analyzing a sample of spring water in a laboratory. Your ion test reveals a sodium concentration ($c_1$) of 23.0 mg/L and a chloride concentration ($a_1$) of 35.5 mg/L. To find the total anionic and cationic mass, you sum all detected species. If these are the only ions present, your total TDS is simply $23.0+35.5=58.5 \mathrm{mg/L}$. To check the ionic balance, you convert these masses to equivalents by dividing by their equivalent weights (ionic mass divided by valence). Sodium gives $23.0/23.0=1.0 \mathrm{eq}$ and chloride gives $35.5/35.5=1.0 \mathrm{eq}$, resulting in a brilliant 0% ionic difference percentage, confirming a highly reliable and electrically neutral water sample.

Always ensure your conductivity meter is properly calibrated with a standard potassium chloride (KCl) solution before taking EC measurements for TDS conversion. Remember that the conversion factor $k$ is not universal; nutrient-rich hydroponic solutions require a different factor than natural mountain streams or brackish groundwater. Finally, when performing ion balancing checks, always verify that your units are consistent—converting micrograms to milligrams prior to summation will prevent massive calculation errors.