To convert grammes to kilograms divide by 1000. I've generated some hopefully helpful examples randomly below, as with most random sentences please excuse the repetitive and occasionally comic outcomes.
How many kilograms of gold are there in 7.3 grammes? Just divide by 1000 to get the answer of 0.0073 kilograms.
You've got 7.5 grammes of emeralds but someone only wants to buy that in units of kilograms, to change the units divide by 1000. Now you have 0.0075 kilograms.
In 0.1 grammes of silver there are 0.0001 kilograms, to achieve this take 0.1 and just divide by 1000.