Of the futon frames you may come across in your search, there are three that are by far the most popular: Bi-Fold, Chair/Love-seat and Ottoman, and the Tri-Fold or A-Frame styles. Each is more or less associated with either a particular size of futon mattress or, philosophy behind the construction.
Of the three we are looking at here, the most popular by far is the Bi-Fold frame, which are most often found with futon mattresses of the Full or Queen sizes.
Full size futons and frames (the most popular of these two) will generally measure 75 inches ‘between the arms’, basically the length of the mattress. To figure the full length of the futon along the wall you will need to add in the width of the arms, generally between 2 and 6 inches, depending on the style. Queen size futons will measure 80 inches between the arms, again, you will need to add the width of both arms to figure the total ‘wall’ length. When in the open position (as a bed), the Full size futon will extend 54 inches from the wall, and the Queen size will extend 60 inches from the wall to the front edge of the mattress. When the futon frames are in the closed position (as a couch or sofa), they will extend from 36 to 42 inches from the wall to the front edge.
The second most popular type of frame is the Futon Chairs and Ottoman and the Love-seat and ottoman. The Futon Chairs and ottomans come in two styles, those with a built in sliding ottoman and those with a separate ottoman. These two styles come in two sizes, and when laid flat they measure either 28 inches by 54 inches (Jr. Twin) or 39 inches by 54 inches (Twin). The 28 and 39 inch measurements are the between the arms figures. When the ottoman is added and the second mattress piece in place, the distance extended from the wall is 75 inches. When the futon is in it’s position as a chair, the extension from the wall is between 36 and 42 inches.
The Love-seat measures 54 inches between the arms and when laid out is a 54 by 54 inch square. Adding the ottoman and second mattress piece brings the futon size to 54 by 75 inches, the same as the Bi-fold full size mattress, but the length and width orientation are reversed. Occasionally the Love-seat futon will use a thinner 1 piece mattress that will drape over the back of the frame when in the closed or upright position.
Finally we have the A-Frame, or Tri-Fold frame style (also called a 3 way frame). These will come in sizes to match their mattress sizes- the most common of which are Twin, Full and Queen. Twins will measure 39 inches wide by 75 inches between the arms, Full size futons will be 54 inches wide by 75 inches between the arms, and the Queen will be 60 inches wide by 80 inches between the arms. The 3 way frame can also be used for a King size futon but that is a much less common size. Some of these styles of frames do not have arms that extend above the frame, these are Low Arm frames. Those that do have arms extending above the frame that you can rest your arms on are called High Arm frames. The mattresses used on these frames are generally thinner and more flexible as they will either be folded under the front part of the ‘sofa’, or draped over the back.
Framing material will typically be either metal or wooden. The metal frames are often less expensive but do not hold up as well as the more expensive but more durable wooden frames.