The average salinity of seawater is

Seawater or salt water is water from a sea or ocean.

On average, seawater in the world's oceans has a salinity of approximately 3.5% or 35 parts per thousand. This means that for every 1 litre (1000 mL) of seawater there are 35 grams of salts dissolved in it.

Hence, The average salinity of seawater is 3.5%.