A standard straight-load trailer designed to haul two horses features an inside stall width of 6 feet, a 10-foot trailer length and a roof height of 7 feet, 6 inches. A standard trailer hauls horses 14 to 16 hands high.
An extra-large straight-load horse trailer has an 11-foot stall and is 6 feet wide with a roof that stands 7 feet, 8 inches tall. An extra-large trailer has a 96-inch-wide axle to account for larger horses and heavier weights. This trailer hauls horses from 16 to 17 hands in height.
There are also double extra-large straight-load horse trailers with axles of 102 inches to haul horses between 18 and 19 hands in height. Some manufacturers also custom build horse trailers based on the horse’s size.