A yard is a unit that mostly used in America and Canadia to measure the length of something field-size, so it's used a lot in sport. One yard equal to three feet, while one foot equals to 12 inches. There is a higher unit than yard called miles which equals to 1760 yards or 1.60934 kilometers.
Since the measurement is 18 yards, the length in feet will be: 18 yards * 3 feet/yard= 54 feet.
The measurement in inch will be: 54 feet * 12 inches/feet = 648 inches.
