Multiply the EC value in µS/cm by 0.64 to get an estimate of salinity in parts per thousand (ppt).

your question needs further clarification

Unit uS/cm does not exist

here you may have in mind

Microsiemens per centimeter µs/cm

or millisiemens per centimeter ms/cm

rarely ds/m or mmhos are useful too

specify which unit you received for conductivity

The coefficient 0.64 or 640, are very approximate, but can be used for rough results

See also this edition of FAO:

https://www.fao.org/4/x5871e/x5871e00.htm

Salt-Affected Soils and their Management

Multiply Conductivity value by 0,64 Abdelkader Hassani

Electrical conductivity is directly proportional to salinity. It is multiplied by 10 to obtain the sum of cations and by 10 the sum of anions. The sodium cation is the most dangerous and the bicarbonate anion is carbonate and chloride.

Converting soil conductivity measured in microSiemens per centimeter (µS/cm) to salinity typically involves empirical relationships or guidelines. Salinity is often expressed in terms of total dissolved solids (TDS) in milligrams per liter (mg/L) or parts per million (ppm). Here's a general method:

Step 1: Understand the relationship

Electrical conductivity (EC) is correlated to salinity because dissolved salts in water conduct electricity. A commonly used approximate conversion factor is:

Salinity (mg/L)=EC(μS/cm)×Conversion Factor\text{Salinity (mg/L)} = EC (\mu S/cm) \times \text{Conversion Factor}Salinity (mg/L)=EC(μS/cm)×Conversion Factor

The conversion factor typically ranges from 0.5 to 0.7 depending on the ionic composition of the solution. For most natural waters:

• 0.55 is used for freshwater
• 0.65 is used for saline or brackish water

Step 2: Apply the formula

Step 3: Adjust for specific calibrations

If you have detailed ionic composition or laboratory-specific calibrations, use the most accurate conversion factor for your data. Advanced methods may involve specific conductance-to-TDS conversions provided for a particular region or water type.