You could (theoretically) use either... However - Kilos is the preferred measurement.
A "large" dog is anything heavier than about 15 kilograms.
kilograms
10 kilograms
grams
825,000
I think it is kilograms
1300 grams
290kg
Kilogram
The weight of a guitar could be determined in either kilograms or grams, but preferably in kilograms.
You would weigh a baseball bat in kilograms.