Because each manufacturer varies, this is an estimate only.
Some companies weigh their trailers empty, without any interior panels or partitions.
This way they claim to be lighter yet. Generally, this is not the case. When comparing trailer to trailer, use the same size and options to obtain a true idea of weight from one brand to another. You will need to know approximately how much your horse weighs in order to calculate the trailer weight when it is loaded. Don't forget to estimate the hay, supplies and equipment you load into the trailer when you are calculating fully loaded weight.