* Grams (g) measure mass, which is the amount of matter in an object.
* Meters (m) measure length, which is the distance between two points.
Think of it like this: you can't say how many apples are in a banana because they're different fruits!
To make a conversion, you need to know the density of the material you're working with. Density is the mass per unit volume, which would allow you to relate mass to volume.
