If the media is water, it is 300 grams
300 ml of water is 300 grams
300g=300mL; 1c = 236.6mL 300g = 1.27c
Millimetres are not an equivalent type of unit to grams unless you are measuring water.
There are 32 grams of sugar in a 300 ml can of coke. There are 4 grams for every teaspoon. 32 grams of sugar equals 8 teaspoons.
You need to know the density of the yoghurt - which can vary.
300 grams of salt is roughly one cup. A typical cup is about 300ml or 250ml of content. When cooking, the accurate measure for salt should be in teaspoons.