Editors Note: This is a guest post by “bunk bed guru” Robert Lobitz. 

One of the top challenges in apartment living can be freeing up enough bedroom floor space to allow you to find room for a dresser or two, as well as two kids’ beds. If your younger ones are sharing a bedroom and space is tight, one of the simplest modifications you can make is setting them up with bunk beds. Stacking one bed atop the other immediately frees up a good deal of floor space that can be used for storage, a desk, or simply left empty as walkways or play space.

When you’re setting up your bunk beds, you may need to buy new mattresses, especially if the beds you’re setting up have been previously used. So you might be wondering whether or not twin bunk beds mattresses and twin bed mattresses are the same size. After all, it’s easier to locate a typical twin bed mattress than it is to find a specialty shop that deals in less frequently used items.

But keep in mind that with bunk beds, there are safety considerations that you must take into account. Bunk beds are responsible for a number of injuries and deaths each year, so following safety procedures is of the utmost importance. Remember, your mattresses should fit your bunk beds as tightly as possible.

The Consumer Product Safety Commission mandates safety regulations on the design of bunk beds and the mattresses that fit them. Regulations state that the mattress must fill the entire bed frame, width and length, and fit snugly into the frame. Spaces left when mattresses are too short or not wide enough for the bed frame pose strangulation hazards. Beds that were manufactured after June 19, 2000, are up to the most current safety regulations.

Most bunk beds work with standard twin mattresses, however some beds are made to accommodate extra-long twin-, full- and futon mattresses, which can come in many different sizes, so it’s a good idea to check manufacturers’ specifications.

While most bunk beds are set up for twin bunk beds mattresses, it’s fairly common to see beds that accommodate a full-sized mattress on the bottom and a twin mattress on top. It’s known as a twin over full. Sometimes, bunk beds are equipped for full sized mattresses on both the top and the bottom, which is logically called a full over full.

Yet other bunk bed models offer a futon mattress on the lower bunk, which can be used as either a sofa or a bed, and either a twin or full mattress on the top. You can purchase futons in sizes ranging from twin to king, so investigate your beds specifications before purchasing a mattress for it.

Mattress widths and lengths are standard, but the thickness of any mattress you buy can vary widely, depending on the manufacturer and which model you choose. Mattress thickness is important for bunk beds, because safety regulations stipulate that your guardrails must extend at least 5 inches above the top of your mattress. Before you buy a mattress, measure the bunk to determine how thick your mattress can be and still allow the guardrail to be at a sufficient height over it.