General rule of thumb 1 kg = 1% bodyfat.
Losing 1 kg of fat each week is possible, but very few maintain that level of fat loss week after week after week, especially dropping into the single digits (especially for women).
If you are competing, it is how you look, the judges will not be up there with calipers.
Also even with calipers used by someone who knows what they are doing, there is a margin of error, which could be 1% easily.