As Reply said, a milliliter (ml) is a measure of volume, while grams (g) is a measure of mass (or weight, makes no difference for your needs). There is no way to tell you have much you need without the density of the powder. Best way is what Reply said, get a scale. Now, if you don’t have one, you can estimate it by making a balance, 30ml of water weighs 30g. Measure out 30ml of water, and put it on a homemade balance and see when it evens out.