There are two factors that affect ocean water density. The most important one is temperature, and the second most important is salinity.

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Salinity is salts dissolved in water that come from rocks and soil. The average salinity of the ocean is 35 ppt (parts per thousand). But, things like melting ice and rivers dilute salty water, so many coastal areas have lower readings. Our oceans vary in salinity too: Near the shores, rivers dilute the ocean to reduce salinity. In the arctic, melting icecaps also affect salinity.

Salinity versus conductivity

We measure the salt content (salinity) or how much electric current passes through water (conductivity). Both are great measurements. The Ocean Explorer Testkit measures salinity, while the Freshwater Explorer Testkit and the Mini Freshwater Explorer measures conductivity! Average conductivity reading for ocean water is about 55,000 µS or 55mS, while salinity averages 35 ppt. For more details on conductivity, go to

Testing salinity with a refractometer (1:36)


This refractometer meter can be found in…