Average 16hh TB will be approx 500 - 525kg if that helps, but you have to allow for water, tack etc as well as the horse weights. And a big warmblood type could be 750kg
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A previous poster has given weights of some horses however you must also take into account other weight to be carried. You must allow for driver & passengers, fuel, water, tack etc. I think you may be able to advertise it as you want however put the unladen weight in any advert, then the decision as to what it can carry has shifted to the buyer.