To convert grams to kilogrammes 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.
You've got 3.8 grams of emeralds but someone only wants to buy that in units of kilogrammes, to change the units divide by 1000. Now you have 0.0038 kilogrammes.
How many kilogrammes of platinum are there in 6.1 grams? Just divide by 1000 to get the answer of 0.0061 kilogrammes.
You have 4 grams of gold but you need to know how many kilogrammes that is. To get the answer divide by 1000 which gives you 0.004 kilogrammes.