How much do rubber ducks weigh?
55.9 grams. And in case you're looking for other units:
279 metric carats
0.123 lbs (that's pound-force to be specific)
0.000055 long tons
0.0000559 metric ton
And, yes, we can prove it!
Note: please, please, please don't use this information to build a bridge or something like that.