We've read about cubits before when Noah built the Ark. But now we read about the Tabernacle and the articles of the Tabernacle. God describes to Moses how these are to be built and He keeps using the word cubit. What even is a cubit? A cubit is a unit of measurement approximately 18 inches in length. This means that any time you come across a cubit in the Bible, it is equal to 1 1/2 feet.
The Ark of the Covenant then is 3 3/4 feet long, 1 1/4 feet wide, and 1 1/4 feet tall.