Those tables I think provide a good general guide when considering towing requirement.If you want to know the weight
of your trailer
however, or one you are considering buying, I'd suggest you find a commercially calibrated scale. They have them anywhere truck load must be calculated to determine payment. I used the one at a recycling yard. To save time for the operator, I weighed car and trailer, then just the car and did the math.
For more information, and since my load varies quite a bit depending on the trip, once I got home I removed and carefully weighed anything that wasn't screwed down to determine the remaining "dry weight" of the trailer. I also kept track of the weights of the various pieces of "cargo" I took out. While some may disagree, I find dry weight useful as a starting point in determining my actual weight, given a certain cargo. I just add the weight of the previously recorded cargo I'm actually carrying, plus anything new. You may not want to be that fussy, but really it can be done mostly in your head.