what are the dimensions of a full size mattress ~~

A standard full size mattress (also called a double) typically measures about 54 inches wide by 75 inches long (approximately 137 cm by 191 cm).

In some guides, you may also see a very close variant listed as 53 inches wide by 75 inches long, but 54 x 75 inches is the most commonly cited standard in the U.S. mattress market.

If you’re buying a frame, bedding, or planning room layout, use 54 x 75 inches as your working dimensions for a full size mattress.