General Appearance: The American Mastiff is a large, massive, powerful dog with a moderately broad head, drop ear, wide set kindly eyes of brown or amber color, the darker the better. This dog possesses a powerful neck, wide deep chest, and muscular back. Tail is wide at the root, tapering to the end, hanging straight in repose, forming a slight curve. The overall appearance should be of proportions slightly longer in body than in height.
Size: Height at maturity is typically 32 to 36 inches for males with an average weight between 160 and 200 pounds. Height at maturity for females is typically 30 to 34 inches with average weights between 140 and 180 pounds. Larger or smaller sizes for both males and females are acceptable provided the dog is in good proportion and structurally balanced.
Bite: Scissors bite preferred, but a moderately undershot jaw should not be faulted providing the teeth are not visible when the mouth is closed.
Coat: The coat must be short and dense. As in other mastiff breeds, a puppy may have a longer coat; this is known as a "fluffy" and is extremely rare but not considered a fault.
Color: Fawn, Apricot, and Brindle. Puppies are all born dark and lighten as they grow. Some dogs may become very light fawn by age one year; some retain dark hairs (not a fault). White on foot, chest, nose and chin is not a fault.
Muzzle: Muzzle must be dark in color, darker the better with same color around the eye orbits and extending upward between them, referred to as the "Black Mask". All American Mastiffs must exhibit the black mask.
Legs: Strong, set wide apart, heavy boned. Feet are large, round, and compact.
Gait: In movement, the gait denotes power and strength; rear legs drive while forelegs track smoothly with good reach
Temperament: The American Mastiff is a combination of grandeur, good nature, and gentleness. These dogs portray dignity rather than gaiety. They are neither shy nor vicious. The well trained American Mastiff is calm, controlled, confident, patient, and loving with their family, especially children. They can be aloof toward strangers. A well-socialized American Mastiff is friendly yet sensitive and alert to changing situations. They are not aggressive by nature but will defend their family if necessary. These dogs respond to threats with judicious warnings and courageous action if needed.