>I would say "... has a mass of ... kg.". Unfortunately, this is more involved than the (incorrect) form: "... weighs ... kg.". AFAIK, there is no corresponding verb, that would make it simpler. This may be because the concept of "mass" is newer than the concept of "weight".

Yeah, even all the metric-based Europeans in my hobby-society use the word "weigh" all the time, never mass. I think weigh is here to stay for a long while.

Hmm...Maybe we should approach it from the other way-round, in this case. Sort of gradually alter the meaning of "weigh" until the primary definition is "to take a mass measurement."