EC-TDS Salinity & dS/m to ppm, and the Class

Electrical conductivity (EC) measures how well water or a soil solution conducts electricity, which rises with dissolved salts; it is reported in deciSiemens per metre (dS/m). Total dissolved solids (TDS) measures the mass of those salts, reported in parts per million (ppm) or mg/L. Both describe salinity from different angles.

They are linked by an empirical factor — for agricultural water and soil the common rule is TDS (ppm) ≈ EC (dS/m) × 640. So an EC of 1 dS/m corresponds to roughly 640 ppm of dissolved salts. This converter applies that factor in both directions and reports the factor it used.

The factor depends on which salts dominate the water. Around 640 suits most mixed irrigation and groundwater, but values from about 550 to 700 are used; high-sulphate or high-bicarbonate waters sit at the lower end and chloride-rich waters at the higher. Use 640 unless a local standard or lab specifies otherwise.

Dissolved salts raise the osmotic pressure of soil water, making it harder for roots to take up moisture — so a salty solution can leave plants drought-stressed even in wet soil. High salinity stunts growth, scorches leaf margins and cuts yield, and sensitive crops suffer well before tolerant ones.

It is a band that tells you how salty the water or soil is and which crops will cope. As a guide for irrigation water, under about 0.7 dS/m is generally safe, 0.7–3.0 dS/m carries slight to moderate restriction, and above 3.0 dS/m brings severe limits suited only to salt-tolerant crops. The converter flags the class for your value.

Beans, carrots, onions, strawberries and many fruit trees are salt-sensitive and decline at low EC. Cereals like wheat and tolerant crops such as barley, cotton, date palm and many grasses handle far higher salinity. Always check the threshold for your specific crop against the EC class.

An EC or conductivity meter reads dS/m directly; many handheld meters labelled TDS actually measure EC and apply a built-in factor to display ppm. For soil, EC is measured on a saturated paste or a soil-to-water extract. Always note the temperature, since EC rises with warmth and meters usually correct to 25°C.

They use the same units but are measured differently — soil EC depends on the extract ratio (saturated paste, 1:1, 1:5). A saturated-paste EC is the standard for crop tolerance thresholds, while diluted extracts read lower and need their own interpretation. Match your reading to the method the thresholds assume.

Yes — leaching with good-quality water flushes salts below the root zone, choosing tolerant crops sidesteps the problem, and improving drainage stops salts re-accumulating. For sodium-affected water, gypsum and management help. Knowing the EC and class is the first step in deciding which of these you need.

The conversion is exact for the factor chosen, but the right factor and the salinity thresholds depend on salt composition, crop, soil and measurement method. Treat the converted value and class as a sound guide, and confirm against a laboratory analysis and your crop's specific tolerance.