Sofa dimensions: length, depth, seat height and arm

Two numbers appear on the label of every sofa sold: overall length and overall depth. Four more decide whether anyone wants to sit on it, and most ranges do not publish them. This page takes all six apart and shows the arithmetic that turns a body dimension into a piece of furniture.

The six dimensions, and the face each is measured from#

Overall length is the widest point of the piece, arm to arm, including any flare. On a square track arm that point is the base. On an English roll or scroll arm it is 6 to 10 in (15 to 25 cm) above the seat and can be 2 in (5 cm) wider than the base, so a sofa planned into an alcove from its base measurement hits the returns with its arms.

Overall depth runs from the front face of the arm or the seat cushion, whichever projects further, to the back of the frame. It is not measured to the face of the back cushion. It is also not the space the sofa takes from a wall, because a sofa with loose back cushions needs 2 to 3 in (5 to 8 cm) behind it for those cushions to stand up rather than be pushed forward, and every wall has a baseboard on it at 5/8 to 3/4 in (16 to 19 mm). A nominal 38 in (97 cm) sofa occupies roughly 41 in (104 cm) of floor, and that is the figure that belongs on your plan.

Seat height is floor to the top of the seat cushion with nobody on it. Seat depth is the front edge of the seat cushion to the face of the back cushion, again uncompressed. Arm height is floor to the top of the arm at its highest point. Back height is floor to the top of the back, measured on a loose-back sofa with the cushions plumped, which is a state the sofa is in for about four minutes a week.

Why the three-seat sofa is 84 in long#

Start at the body. Seated hip breadth is about 14 in (36 cm) at the median and 16.5 in (42 cm) at the 95th percentile, and elbow to elbow breadth is 19 to 20 in (48 to 51 cm). Sitting with the arms in needs 22 in (56 cm) of seat width; sitting for an evening wants 24 to 30 in (61 to 76 cm). So a three-seat sofa needs between 3 x 22 = 66 in (168 cm) and 3 x 26 = 78 in (198 cm) of seating. Then add the arms, and two sofas of identical overall length stop being the same sofa:

An 84 in (213 cm) sofa with track arms gives 76 in (193 cm) of seat: three comfortable places at 25 in (64 cm) each. The same 84 in with an English roll arm gives 66 in (168 cm), which is three tight places at 22 in (56 cm) or two good ones. The arm is worth 14 in (36 cm) of seating, and 14 in is most of a person.

That explains why the trade sizes settle where they do. Two seats plus track arms is 2 x 26 + 10 = 62 in, and loveseats are made at 58 to 64 in (147 to 163 cm). Three seats is 3 x 25 + 10 = 85 in, and sofas are made at 84 in. Four is 4 x 24 + 10 = 106 in, and the large sizes run 96 to 108 in (244 to 274 cm) before a range switches to sectional modules.

Loveseat 60 in, sofa 84 in, four-seat 106 in#

The depth column is where national habit shows. British and European three-seat sofas cluster at 34 to 38 in (86 to 97 cm), North American ones at 38 to 42 in (97 to 107 cm), a 4 in (10 cm) gap that decides whether an imported sofa leaves a walkway. The comparison is in furniture sizes, UK versus US.

Where the 38 in of depth actually goes#

Overall depth is the sum of five parts, and knowing the split tells you what a sofa will feel like before you sit on it. For the 38 in (97 cm) sofa in the figure above:

• Back frame and upholstery: 3 in (76 mm)
• Back cushion, uncompressed: 8 in (203 mm)
• Seat cushion, front to back: 24 in (610 mm)
• Front overhang or arm projection: 3 in (76 mm)

That gives 38 in. But the effective seat depth, back cushion face to front edge once someone leans on it, is not 24 in. A back cushion compresses 2 to 3 in (5 to 8 cm), so the seat you get is 26 to 27 in (66 to 69 cm) deep.

Compare that with the body. Buttock to popliteal length, hip to the back of the knee, is 17.3 in (44 cm) at the 5th percentile and 21.5 in (55 cm) at the 95th. A 26 in effective seat leaves even a tall adult with 4.5 in (11 cm) of cushion under nothing and a shorter adult with 9 in (23 cm), so you cannot reach the back and keep your feet down at once. The percentile range is in seat height, depth and angle.

This is not a fault. It is the design brief of a deep-seat sofa: the customer is meant to recline, or to fill the gap with a lumbar cushion 5 to 6 in (13 to 15 cm) thick, which is why deep-seat ranges ship with more scatter cushions than shallow ones. The sizes those cushions come in are set out in cushion, pillow and throw sizes.

The 2 in a cushion loses under an adult#

Seat height and the popliteal limit#

Seat height is set by popliteal height, floor to the underside of the knee with the foot flat, which runs from about 15.5 in (39 cm) at the 5th percentile of adult women to 17.5 in (44 cm) at the 95th of adult men. A compressed seat at 17 in (43 cm) lets almost everyone put their feet down. Below 15 in (38 cm), standing up needs the arms, which is why ageing in place dimensions pushes seat heights up rather than down.

Arm height, back height and the furniture around them#

Arm height at 24 to 27 in (61 to 69 cm) governs the furniture around the sofa rather than the sofa itself. A side table top belongs within 2 in (5 cm) of the arm, so a 25 in (64 cm) arm wants a 23 to 27 in (58 to 69 cm) table, and the bands are in side table and console heights. Arm height above the seat also decides whether the sofa can be slept on: 7 to 9 in (18 to 23 cm) of arm above the compressed seat works as a headrest, and a 2 in (5 cm) arm does not.

Back height at 30 to 36 in (76 to 91 cm) supports the shoulder blades of a seated adult, whose shoulder sits 21 to 24 in (53 to 61 cm) above the seat. Backs above 38 in (97 cm) approach seated eye height at 46 to 48 in (117 to 122 cm) and start to divide a room, which is fine against a wall and poor in the middle of a floor. A sofa dividing an open plan space belongs at the low end, 30 to 32 in (76 to 81 cm), with a console behind it.

Deep seats, sofa beds and a 32 in door#

• A deep-seat range. Four extra inches (10 cm) of seat depth add 4 in to the overall depth and push the coffee table 4 in further out, because the gap is measured from the cushion face. The room pays 8 in (20 cm), not 4.
• A sofa bed. The frame is deeper and heavier, and the opened footprint is a separate problem set out in sofa bed and daybed dimensions.
• Leg height. A 6 in (15 cm) leg under the same frame changes nothing functional and changes the visual weight sharply, which is the subject of furniture leg heights and visual weight.
• Bench seat versus separate cushions. A bench cushion has no seat divisions, so the seat count is pure arithmetic on the seating width and nobody is forced onto a seam.
• The door. A 38 in (97 cm) deep sofa goes through a 32 in (81 cm) clear door on its side, which needs the diagonal of its height and depth to clear. Run the delivery path before ordering.

All of it sits inside the wider set of sizes in furniture dimensions, and the sofa and seating fit checker runs the same chain of clearances against your own room.