You can convert 30 millilitres to grams using a simple equation, provided you know the specific density of the item you have 30 millilitres of. Any measurement of volume carries with it a corresponding weight; however, different gases and liquids have specific densities that will affect their weight. The ratio of volume to weight, millilitres to grams in this instance, will vary according to the substance to be measured.
Write down the volume in millilitres (ml) of the substance you want to know the weight of in grams (g). In this instance, write down 30 since you are trying to discover the gram weight of 30ml of a substance.
Using a specific density chart, locate the gram per millilitre ratio for your substance. For example, suppose you want to find the gram weight of 30ml of water. Water has a ratio of 1 gram to 1 millilitre (1:1). Write down (1) below the number of millilitres (30) that you want to convert to grams.
Multiply the volume of your substance by the grams per millilitre of the specific density of the substance. In this instance, if you have 30 millilitres of water, you will multiply the volume (30) by the density (1).
The solution to your equation is the amount of gram weight in the volume of your substance. In the example, 30 millilitres of water multiplied by the density of water (1) will give you an answer of 30. Since this is an equation to convert millilitres to grams, the correct way to write the answer is 30g (or grams).
Since a cubic centimetre (cc) is equal to a millimetre (ml) in volume, you can use the same equation if your substance is measured in cubic centimetres to discover the weight in grams (g) of your substance.
Always know the exact nature of the substance before consulting the specific density chart. Mislabelling your substance will provide you with the wrong ratio to use in your equation.