Are Two Twin Box Springs the Same Size As a Queen Mattress?

Placing two of them together would give you too much width and not enough length. Even though an extra-long twin box spring is long enough at 80 inches, placing two side-by-side would result in 76 inches in width, which is 16 inches wider than a queen mattress. However, two extra-long twin box springs put together are the correct size to hold a king-sized mattress.