How wide was the largest snowflake ever recorded?

In 1887, a 15-inch wide snowflake fell on the Fort Keogh Army Post in Montana that is still considered the largest ever.

The Giant Snowflake which was said to be the largest ever seen was witnessed by the Army personnel who were posted at Fort Keogh, which was a post in the United States of America located on the western side of the then-Territory of Montana, two years before Montana was admitted to the Union as the 41st U.S. State.

Here, the most important news appeared after the people saw the largest snowflake ever amidst a snowstorm which was falling upon the fort named after U.S. Army Captain Keogh who died while fighting for that same post. The snowstorm which was being witnessed by the soldiers saw some 15-inch wide snowflakes fall, and it is said that snowflakes of their breadth and thickness were being witnessed for the first time in human history.