The word "specific," when used in physics and chemistry, has a (specific) meaning. It refers to a quantity divided by an extensive (dimensional) measure to make it a measure of a substance's properties instead of peculiar to a particular object. For example, specific conductivity (or just conductivity, which by definition already is a specific measure) measures a substance's ability to conduct electricity. Scientists measure conductivity in seawater to determine salinity. While the conversion from the former to the latter uses a long equation of several terms, you can use an online calculator to make the conversion with just three variables.
Convert your conductivity measurement's unit from siemens per meter (S/m) to milli-siemens per centimetre (mS/cm). In other words, multiply by 10.
Raise the conductivity (in mS/cm) to the power 1.0878.
Multiply the result by 0.4665. This gives you salinity in grams (of salt) per litre (of solution).
An accurate conversion for salinity ranges 5 to 100 milli-siemens per centimetre, or 0.5 to 10 S/m. This is useful for aquariums, freshwater and saltwater. The above parameters apply to 25 degrees Celsius.