Rating Newest Oldest. Best Answer: http://www.wikihow.com/Make-a-Coffin gives all the measurements. A casket is a little different. The average length of a casket is 84 inches; width 28 inches, and height 23 inches.ating Newest Oldest. Best Answer: http://www.wikihow.com/Make-a-Coffin gives all the measurements. A casket is a little different. The average length of a casket is 84 inches; width 28 inches, and height 23 inches.