According to The John Shone Collection, a traditional grandmother clock is a shorter, narrower version of a grandfather clock. The grandmother clock has a long case and a large dial or face. It runs by a spring or pendulum system.
Many grandmother clocks were manufactured during the 1920s and 1930s. The most popular sizes were between 5 feet, 4 inches and 5 feet, 9 inches tall. Typically, if a long case clock is over 6 feet, 3 inches, it is categorized as a grandfather clock. Even smaller versions are known as granddaughter clocks. These stand 5 feet, 2 inches tall or less. Because their cases are often veneer over plywood, granddaughters tend to be of lower quality than the grandfather or grandmother clocks.