A sofa is usually the largest piece of furniture in a room and should be scaled to fit both the space and its occupants. Doorway and stairwell dimensions are critical for sofa choice as the most beautiful piece of furniture in the world will be useless if it won't fit through your doorway or up your staircase. Standard sofas measure 40 inches in depth from the front edge of the cushion to the back of the sofa frame.
Sofa frame depth and seating depth are two separate things. A sofa that is 40 inches deep may have thick, 8- to 10-inch cushions lining the back frame. The cushioning narrows the actual seating depth to 32 or 30 inches, respectively. A few inches may make a big difference if the sofa owner is taller or shorter than average. Sitting on the sofa in the showroom is the best way to determine the optimum depth for you.
The diagonal depth of a sofa will determine whether it can be moved into your living space. To determine diagonal depth, use a straightedge to measure your sofa from the highest point of the back frame to the front of the arm, and measure from the bottom rear corner of the sofa to the point that bisects the straight edge. If diagonal depth exceeds door frame width or stairwell clearance, choose another sofa.
A sofa outfitted with bulky seat and back cushions will alter how the furniture feels when you sit down. If you sink down into the sofa, you may wish to adjust sofa depth so that you can extract yourself gracefully. A shorter depth measurement is preferable for particularly bulky furniture. Sofas that have thinner seat cushions and less padding in the back may require greater depth to produce a comfortable sitting position.
Many manufacturers offer space-saving sofas with frames as small as 30 inches deep. Usually, the smaller-framed models feature a less bulky frame back and softer seat and back cushions to compensate for shorter frame depth. Larger customers sink in and back more than smaller users, so the shorter frame can work for both. Particularly tall or short clients can have a sofa tailor-made to meet their physical requirements. The comfort of a custom-made sofa may be worth the extra cost for these customers.