Chet has 120 ounces of milk in a container. After he fills 7 glasses with the same amount of milk, there are 8 ounces of milk left in the container.
The total amount of milk used to fill the glasses is 120 - 8 = <<120-8=112>>112 ounces.
Therefore, each glass is filled with 112 / 7 = <<112/7=16>>16 ounces of milk. Answer: \boxed{16}.