Why the doorway is a red herring
A doorway is a flat opening and a sofa can be presented to it at any angle you like. A staircase turn is a three-dimensional problem: the width of the stair, the height of the ceiling above the turn, the newel post in the corner and the depth of the half-landing all constrain each other at once.
That is why a piece that walks through the front door can still be stuck three steps up, and why "it came in, so it will go out" is not reliable — it may have come in before a wall went up, or before the bannister was replaced.
How to measure it
Four numbers, taken with a tape, in this order:
- The clear width of the staircase at its narrowest, post to wall.
- The depth of the half-landing from the top step to the far wall.
- The ceiling height directly above the turn — this is the one people forget.
- The diagonal of the item itself: its longest face corner to corner, not its listed dimensions.
Wimbledon’s particular problem
Converted Victorian terraces around the town were subdivided long after they were built, and the stair that serves an upper flat is frequently the original one with a partition wall added beside it. That combination produces the tightest turns in SW19.
Mansion blocks on the park side have the opposite issue: handsome, generous stairs with a sweeping turn that is nonetheless useless for a corner sofa, and a lift that will not take a mattress.
When it will not go
There are three honest options and it is much better to choose between them in advance than on the day:
- Take it apart — many sofas have removable feet, backs or arms, and most wardrobes were flat-pack once.
- Go through a window — real, occasionally sensible, and it needs planning, equipment and usually permission.
- Do not take it — sell it, and buy something that fits the property you are moving into.
Ask before you buy
If you are buying furniture for a property you have not moved into yet, measure its turn first. It is far cheaper to discover the problem in a shop than in a stairwell.