
Your approved tow bar should have a ball weight rating. If it’s a bar from the vehicle manufacturer you’ll find a rating on the label somewhere on the bar or around the inside of the door aperture.
Aftermarket towbars will often have it stamped on the bar or marked on a plate attached to the bar.
The amount of weight you exert on the tow ball via the hitch and draw bar is critical to your trailer and tow vehicle performance, as well as the safety of yourself and others using the road. Exceeding that rating is dangerous to all and sundry so to check your situation have a trailer outlet weigh your rig.
If you want to check it yourself ensure the trailer is carrying its normal payload in the normal position. By the way, any payload must be secured so as not to alter the tow ball weight due to the load shifting position in transit.
Under the hitch, place the jack on a set of scales (some bathroom scales might be calibrated high enough for this). Release the hitch after chocking the wheels and utilising a hand brake on the trailer. Jack the drawbar up until it lifts off the ball and read the scales, subtracting the weight of the jack and any other material used in the procedure.
You now have the tow ball weight. Be mindful that water tanks in caravans and fuel tanks in boats will alter the end result at the tow ball depending on their content volume and variations from time to time.