Ideally kilograms or tons.
Grams.
The answer will depend on what aspect you wish to measure: its length, thickness, its mass or some other aspect.
The gram.
kilograms
You can use any unit to measure mass. I presume you mean a unit which will make the number a sensible size. Either kilograms or tonnes can be used, you just put the decimal point in a different place. The average mass of a female Asian elephant is about 2700 kg, or 2.7 tonnes, and a bull African elephant is about 5500 kg or 5.5 tonnes.
in tons.
TONS.
Tons.
Grams.
A ton for a rough and ready measure. A tenth of a ton (100 kilograms) if you were a biologist following the elephant's development in more detail.
Grams.
The kilogram.
Kilograms.
Kilogram
The gram.
kilograms
The answer will depend on what aspect you wish to measure: its length, thickness, its mass or some other aspect.