Joining two twin mattresses into a king-size bed gives you the space of a king, but the comfort of your own mattress. If you already have the twin-size mattresses, it's an inexpensive way to create a large bed. It's also a good way for couples to get comfortable rest without sleeping alone. Each person can choose the mattress that's right for his sleeping style.

Supplies

You'll have to do more to join a pair of twin beds than simply push them together. The small gap between the mattresses can make sleeping on the seam uncomfortable, and bed frames on wheels may roll apart. Purchase a specialized foam adapter kit to join the two beds, or make your own out of egg crate foam. This insert, or bed bridge, is a long strip of polyurethane foam that rests over the mattress gap. Hold it in place with your fitted sheet or, for more security and comfort, with a soft mattress pad. If your bed frames are wheeled and do not have a locking mechanism, you may also need to tie the middle legs together or use a ratcheting strap to keep the beds from rolling apart.

Size

Twin beds come in two sizes, regular and extra long. In the United States, regular twin mattresses are 75 inches long and 39 inches wide. Extra long twin mattresses are also 39 inches wide, but they are usually 80 inches long. The length of your twin mattress will affect how king-size sheets fit on the joined beds. A regular king-size mattress is 76 inches wide, equivalent to a little less than two twin mattresses, and 80 inches long. Choose sheets intended for extra tall king-size mattresses to avoid fit issues. If you have regular twin mattresses, you may need to tuck in excess sheet fabric at the foot of the beds. Avoid California king sheets, which will be too long and too narrow for your joined twin mattresses.

Tips

Keep both king-size and twin-size bedding on hand. You may need to use the beds separately for guests or after a move. You can use a sheepskin bed bridge to eliminate the between-bed gap if you prefer natural materials to petroleum-derived foam. If you have extra long twin mattresses of similar softness, you can also join them together sideways to create a wider bed that still fits king-size sheets.

Source:

Comfort House: Bed Doubling System

Dormia Mattresses: Mattress Dimensions and Bed Sizes by Dormia

MattressSizes.info: Twin Mattress & Twin XL Size

More Information:

Bed, Bath and Beyond: Instant King Twin Bed Bridge

Improvementscatalog.com: Create-A-King Twin Bed Connector

Beachcomber.com: Twin Doubler