I feel I need to arrest you a bit Geo
Percent is a measure without denomination.
So if it is kilos, tons or featherweight it do not matter.
It is a certain part per parts just like ppm and ppb.
1 % is one part per cent (100)
1 per mil (not used much in the US)
Is 1 part per 1000
1ppm is part per million
and so on.
They are all unit agnostic and can be used for grams, tons chicken or anything else for that matter.
So 1% is the original weight times 0.01
I have no idea where you find the 0.0045?
But anyway 0.001% of one metric ton is about 10 grams, good for industrial gold ore but not for pins