You also may consider extra features that are available with some trundle bed mattresses, taking into account how often the bed and the specific features will be used. If you plan to use the trundle bed mattress yourself, or frequently have guests who will sleep on it, then you may consider paying a little extra for it to be more comfortable and longer-lasting. For instance, you can buy a trundle bed mattress that is resistant to both stains and water and also is fire retardant. In addition, some mattresses offer extra padding so guests can be particularly comfortable as they sleep.
If you do want the ability to store a trundle bed mattress under the main bed, then you should measure the space you have available to make sure the mattress can easily fit. If you already have a trundle bed mattress, then you can measure that to determine what dimensions to look for in a new one. If you bought the bed without a mattress, then you should measure the trundle to find out how large of a product you should buy. You probably will need to take into account the width, length and height of the space you have for the mattress.
The Ultimate Pop Up Trundle Bed top mattress measures 78.7" x 39.5" x 9" which is the size of a twin extra long. And the bottom measures 74" x 38" x 9", which is the size of a standard twin mattress. The primary bed base stands 13" tall. This puts the top of the mattress 24.5" off the floor. The second bed, hidden cleverly underneath the first, may be used either in the lowered position, or the raised position to create a combined king size mattress sleep surface. The top trundle bed mattress requires a twin XL sheet and the lower mattress uses a regular twin size sheet. It is also possible to cover both the twin size mattresses with one king size sheet.
Please note the top mattress is 15 cm longer than the trundle mattress
This allows the trundle bed to be stored under the top mattress
The sizes above are for the space allowance required