Bob Scott said:Force/mass conversions can be confusing. In metric, KG can be used for weight and mass. The unit of force is the Newton. In Imperial, Pounds can be used for weight and force. The unit of mass is the Slug.
Well, it's actually mass all the time. BUt people just say the weight is 5kg. BUt because they say kg it's still mass. THe fact that the bag of potatoes weighs 10lbs doesn't work if you aren't on earth (or it doesn't have the same meaning rather).