Read both kinds of depth
The overall depth runs from the back of the sofa to its furthest point at the front. Seat depth describes the space you actually sit on. A thick back or a projecting frame can use room without adding much sitting space, so compare the product drawing rather than treating these figures as interchangeable.
If dimensions are unclear, ask the retailer how they are measured. Loose back cushions, curved arms and reclining mechanisms can complicate the outline. A recliner has more than one footprint: it needs space when open as well as when closed. Include any required clearance behind it before deciding that it will fit against a wall.
Test the person and the room
A deep seat may suit someone who likes to curl up, but another person may find their feet no longer rest comfortably when their back is supported. A shallow model can make a narrow room easier to cross yet feel too upright for evening lounging. Sit as you normally would, with the cushions that come with the sofa.
At home, mark the external depth on the floor and compare it with the furniture opposite. Include the coffee table, cabinet handles and the movement of drawers. The useful result is not the amount of bare floor on a plan but whether you can stand up, walk through and reach nearby surfaces without repeatedly shifting something.
The height and shape of the arms also affect how large the sofa appears. A compact frame with bulky arms can dominate a small room, while a longer low-armed model may feel less imposing. Treat that as a visual judgement, separate from the hard measurement of whether the route remains usable.
Change the arrangement before shrinking the seat
If a comfortable sofa is slightly deeper than expected, try removing the central table or choosing a shallower opposing unit before rejecting it. Small side tables sometimes release more useful space than losing comfort from the seat used every day. But do not solve one problem by placing those tables in doorways. The final choice should suit both the sitter and the room around them.
