A ball mount should place the trailer near level when connected according to the trailer and hitch manufacturers' instructions. The basic measurement compares the tow vehicle's receiver height with the level trailer's coupler height.
Measure on level ground
Park both the tow vehicle and trailer on flat, firm ground. Load the tow vehicle approximately as it will be used. Level the trailer with its jack before measuring coupler height.
Use consistent measurement points
Different hitch instructions can specify slightly different reference points. Follow the ball mount or hitch manufacturer's procedure. The simple relationship is receiver reference height minus level coupler reference height. A positive difference calls for drop; a negative difference calls for rise.
Account for loaded suspension height
The back of the tow vehicle can settle under hitch load. If you estimate drop using an unloaded receiver height, the final trailer attitude can differ after connection. Recheck the combination loaded and connected.
Do not exceed ball-mount ratings
Adjustable and fixed ball mounts have weight ratings. Correct height does not make an underrated hitch component acceptable. Verify the receiver, ball mount, hitch ball and coupler ratings.
Frequently asked questions
Should a trailer be perfectly level?
Follow the trailer manufacturer's guidance. Many setups are intended to tow level or very close to level, but suspension and hitch instructions can affect the final adjustment.
What if I need 3.3 inches of drop?
Use the adjustment method and available sizes recommended by your hitch manufacturer, then verify the connected trailer attitude rather than relying only on rounding.