It's mass is almost exactly a kilogram but annoyingly not exactly. It's weight depends on many things but is not measured in Kilos On earth it would weigh about 9.8 Newtons
If you're worried about a difference of about 25ppm (one litre of water, at a pressure of one standard atmosphere, and at it's maximum density temp of 3.98 Celsius (ok, 277.13 Kelvin if we're working in SI) weighs 0.999975 kg, which is close enough for government work.
The SI committee are going to look at redefining the Kg as a fundamental physical property which can be replicated by national measurement labs at their next meeting. Things in metrology don't move quickly though, their next meeting will be in 2014!
Slightly less useful in BC circles is, 1.6 mm equals 1/16" equals 16swg...............roughly! Easy to remember and most everything else you need can be worked out from this. (courtesy of the Battle Damage Repair Bible.)