Checking a couch on the stairs
The tool opens on a straight flight of 14 steps, 7½ inches high and 10 inches deep, 36 inches wide with 6 feet 8 inches of headroom: the minimums in the International Residential Code for a new US home. Change them to your stairs. For a sofa carried low, take the width between the handrails. For the headroom, stand a tape on the nose of a step under the lowest bit of ceiling (often where the upstairs floor ends over the flight) and read it at that edge. Then measure a step, how tall and how deep, and count them. If the stairs turn, choose the landing and enter its headroom.
How the stairs are checked
Seen from the side, the stairs and the ceiling above them form a sloping tunnel between two floors. One of the sofa’s three sizes has to go across the stairs and be narrower than them; the planner then rolls and slides its side outline through the tunnel, starting with the sofa standing as it normally does downstairs, so any tipping at the bottom is checked too. The tight places are usually the ceiling edge over the lower steps and the top nosing.
The tunnel along the flight
Headroom is measured straight up, but the stairs slope, so the room square to the slope is smaller: the headroom times the cosine of the stair’s angle. Along the flight, the sofa’s side facing up has to be thinner than that. The table below works it out for a few common stairs; the ends of the flight are usually tighter still, which is where the tool’s planner earns its keep.
If it doesn’t fit
Unscrew the legs first; carry it higher, above the handrails, where the stairs are wider (enter that width to check); unscrew a handrail if it can come off; and look for another way in, such as a window upstairs or an outside door. For a sofa that won’t go either way, sectional and modular sofas come apart.
Room along the flight
The headroom measured straight up, turned into the room square to the slope, for a few common stairs. Along the flight, the side of the sofa facing up has to be thinner than this; at the ends of the flight it is usually tighter.
| Stairs | Angle | Headroom | Room square to the slope |
|---|---|---|---|
| US: 7¾ in steps, 10 in deep (the IRC limits) | 37.8° | 6 ft 8 in | 63¼ in |
| US: 7½ in steps, 10 in deep | 36.9° | 6 ft 8 in | 64 in |
| US: 7 in steps, 11 in deep | 32.5° | 6 ft 8 in | 67½ in |
| UK: the steepest private stair, 42° | 42.0° | 2.0 m | 1486 mm |
| UK: 200 mm steps, 250 mm going | 38.7° | 2.0 m | 1562 mm |
Sources, checked September 2026: International Residential Code 2021, section R311.7, stairways (width R311.7.1, headroom R311.7.2, risers at most 7¾ in and treads at least 10 in R311.7.5; via UpCodes); UK Government, Approved Document K (private stairs: rise 150–220 mm, going 220–300 mm, pitch at most 42°, headroom at least 2 m).