Weighing your car, truck, motorhome or trailer is fairly simple. All you need to do is find a scale to put it on. You can find them at most truck stops (Flying J), large recycling centers, waste transfer stations, and along most major highways. Some are free, othere may have a small fee. Check them out first before you take your rig there so you'll now what to do.
How to weigh is fairly simple, but it will depend on how long you are and how many individual scales there are.
Most truck stops have 3 separate platforms, so this makes it easy. Positon your rig so that each axle (or pair of axles) is on a separate platform and get a weight reading.
If there are only 1 or 2 platforms available, use them the best way you can to get individual axle weight readings. If it is just one long platform, pull onto (or off) the platform one axle at a time and get a reading. You'll need to do a little math to figure out how much weight is really on each axle. If there is someone working the scales, they may be able to help you with this.
Once you have your weight readings, compare them to the vehcile or trailer's GVWR and GAWR's for each axle. Also compare the total weight of vehcile and trailer to the GCWR.
DO NOT EXCEED THESE RATINGS!!! They are there for a reason...your safety and everyone else on the road.
Also check the load capacity of your tires. Each axle weight reading should be less than the combined weight rating of each tire. It's not uncommon for the GAWR to be more than the combined weight rating of each tire, and that's fine, but we really don't care about that. It's the GAWR we want to pay attention to.
If you are over any of the ratings, you'll need to lighten the load somehow. If it's a GAWR you're over, it could be as simple as moving things around. But if it's the GVWR or GCWR you're over, you need to take something out to lighten the load.
If you're looking at buying a new or used RV, it would be best if you could take it to a scale and get it weighed first because sometimes the "dry" weights listed in the sales brochures or on labels inside the RV are not as accurate as you would hope.