Ball mount drop & rise calculator

How to measure for a ball mount

Do this on level ground, with both the tow vehicle and the trailer loaded to towing weight and tires at their towing pressure:

• A — height from the ground to the top of the empty receiver tube on the tow vehicle.
• B — height from the ground to the bottom of the coupler, with the trailer level.

The formula

Drop or Rise (inches) = A − B. A positive result means you need a ball mount with that much DROP; a negative result means a RISE of the same amount. Measure with both vehicle and trailer loaded to towing weight and tires at towing pressure, allow about 1–2" for the rear to squat once tongue weight is applied, then re-check that the trailer sits level after hookup and fine-tune within about ±1".

Illustrative: receiver top 23" − coupler bottom 19" = a 4" drop.

Drop vs rise — what's the difference?

On a ball mount, the drop is how far the ball platform sits below the shank that slides into the receiver, and the rise is how far it sits above. If your tow vehicle's receiver is higher than the trailer coupler (common with trucks and SUVs), you need a drop. Lift the vehicle or tow a tall trailer and you may need a rise. Many ball mounts can be installed either way up to switch between the two.

The measurement targets the ball-platform height; the ball’s own height isn’t added as a separate term because the coupler socket seats down over the ball near the platform. (This is the standard A−B method used by hitch makers.)

Then check tongue weight

Leveling is about geometry; safety is about load. Once the trailer sits level, confirm your tongue weight is in range and your hitch class and hitch ball are rated for the trailer.