The correct futon mattress size typically depends on what you are trying to determine in regard to the size of the futon. If you want to know the size in order to get a cover for your futon, then you should measure the mattress and compare the size to established guidelines for mattress sizes. On the other hand, if you are trying to determine the best futon mattress size for your needs before buying a futon, then you should consider your personal needs and the space in which you will be placing the futon.
If you already have a futon and mattress, and you are trying to determine the correct futon mattress size so you can buy sheets or a cover, then you should measure your mattress and determine its size from that. Some mattresses may be labeled as king or full size, but you may still want to physically measure the mattress to ensure accuracy. To determine your futon mattress size, you should clear space on the floor if possible, remove the mattress from the futon and lay the mattress on the floor.
You can then use a tape measure to determine your futon mattress size. In general, futon mattresses use the same size scale as standard bed mattresses, so your measurements will determine the size of your mattress. A twin or single size mattress is typically about 39 inches (almost 1 m) by 75 inches (around 1.9 m) in size, a full or double mattress is about 54 inches (1.37 m) by 75 inches (just over 1.9 m), a queen size is 60 inches (about 1.5 m) by 80 inches (about 2 m), a California king is 72 inches (about 1.8 m) by 84 inches (around 2.1 m), and a standard king size is 76 inches (about 1.9 m) by 80 inches (about 2 m) in size.
If you do not have a mattress or futon yet, and you are trying to determine what futon mattress size will best suit your needs, then you should consider your body and the space you have available for your futon. You should try to get a futon and a mattress that will fit you as well as possible. If two people will be sleeping on the bed, then this can be even more important.
The available space for a futon is also quite important when choosing a futon mattress size. You should measure the area you have available for your futon so you get a sense of what will fit. The frame of the futon may increase the size requirements of the mattress itself, so you should take that into consideration as well. While a larger mattress is usually more comfortable for someone who is especially tall or for two people, the physical space required for such a futon can be considerable.
