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Can you scan a room that's full of furniture?

Yes — but the wall behind the bookcase never gets measured, and that's where the error creeps in. Here's how much furniture shifts the numbers, and the four moves that save a furnished room.

Furniture in the middle of the room isn't the problem

A coffee table, a dining table, a chair or a floor lamp in the middle of the floor doesn't ruin a LiDAR scan. The phone still sees the walls all the way round — it just has to walk around the furniture. In fact, furniture helps the phone keep track of its own position, because it gives the camera something recognisable to look at. A completely empty, freshly painted room is actually harder to scan than a furnished one.

Only one thing ruins the measurements: furniture that covers a wall surface. Anything standing flush against the wall and taller than half a metre is a risk.

What happens behind the bookcase

LiDAR can only measure what it has a clear line of sight to. If a 40 cm deep bookcase runs along the whole living-room wall, the real wall is invisible to the phone from floor to bookcase top. The scan then has three options, and all three happen in practice:

• The front of the bookcase becomes the wall. The room ends up 40 cm narrower than it actually is.
• The bookcase is read as a piece of furniture, and the wall behind it is guessed. Then the measurement is correct — if the guess was right.
• The wall is caught through a narrow gap between two pieces of furniture, or above them. Then the measurement is correct, for the right reason.

You can't tell from the floor plan which of the three happened. That's why a room with furnished walls is always a room worth double-checking.

Do the maths yourself

Example: a living room that in reality is 420 cm wide and 520 cm long — 21.8 m². Along one long wall stands a 40 cm deep bookcase; along the opposite wall a sofa with its back to the wall, 90 cm deep.

If both fronts become the wall, the scan measures the width as 420 − 40 − 90 = 290 cm. The area comes out at 2.9 × 5.2 = 15.1 m² instead of 21.8 m² — 31% too little. If the living room needs new flooring, you're missing a third of the material.

That sounds extreme, but it's exactly the error you need to know about in order to recognise it. And it's easy to spot: a room that feels spacious but measures small is almost always a room with furnished walls.

The four moves that save a furnished room

1. Scan at two heights

The most important move. Walk one lap with the phone low, so the floor edge and the skirting board are captured wherever the wall is clear. Then walk a second lap with the phone lifted above the height of the furniture — above the bookcase, above the sofa back, above the headboard — so the camera sees the clear wall up there.

The wall is vertical. If the scan catches the top metre of it, it knows where the wall stands, all the way down.

2. Use the gaps

There's almost always a spot where the wall is clear: between the bookcase and the wardrobe, in the corner, behind the door, above the radiator. Walk close to each of those gaps and let the phone look at them for a couple of seconds. One good look at the real wall is worth more than three laps in front of the furniture.

3. Move what can be moved

If you're going to use the measurements for something that costs money — flooring, a kitchen, a built-in wardrobe — take the five minutes and pull the sofa 20 cm away from the wall before you scan. You don't need to empty the room; you just need to give the phone a strip of clear wall to measure.

4. Verify with a tape measure

If a whole wall is covered corner to corner by a fitted wardrobe, no scan gets through it. Measure the room's width with a tape measure at a clear stretch — for example above the wardrobe or in the doorway — and compare it with the scan. One figure settles whether the scan guessed right.

The furniture on the drawing isn't the same as the furniture's measurements

A piece of furniture in a scan is a different thing from a wall. The wall must be measured accurately, because it determines the room's area. The furniture is there to make the floor plan readable — so you can see what the room is used for and where there's space.

That's why you shouldn't use a scan to decide whether a wardrobe fits into a specific spot to the centimetre. The scan can easily tell you that there's roughly 90 cm between the sofa and the wall. If you're ordering a piece of furniture that has to fit exactly into a niche, measure the niche with a tape measure — every time, no matter how good the scan is.

The rooms that are hardest

• The bedroom. The bed fills half the floor, and there's typically a wardrobe running along a whole wall. Often the hardest room in the home to scan accurately.
• The children's room. Densely packed, lots of small items, furniture right into the corners.
• The kitchen. Units at two heights along two or three walls — the real wall is only visible above the wall cabinets and below the worktop.
• The office and utility room. Shelving to the ceiling, often on several walls.
• The basement room. Full of boxes, poor lighting and few recognisable details at once.

Those rooms should always get a follow-up check with a tape measure if the measurements are going to be used for anything beyond a rough overview.

How to spot it on the drawing

You can catch the furniture error without measuring anything, once you know the signs:

1. A room that's narrower than its neighbour, even though you know the exterior walls run straight.
2. A wall with a kink in it, where you know there's a bookcase or wardrobe standing.
3. A room whose area doesn't match how big it feels — that feeling is actually reliable and should always trigger a check measurement.
4. Two rooms that overlap or leave a gap between them on the plan, because one of them came out too narrow.

What HouseSense does

HouseSense works in internal measurements — from wall face to wall face — so the figure the app shows is exactly what you'd get by stretching a tape measure across the room. That makes a check-up possible in thirty seconds per room.

On the floor plan, furniture is shown as flat rectangles, the way an architect would draw them: they're there to show what the room is used for and where there's space — not as the definitive word on the furniture's own dimensions. Walls and areas are what's measured accurately; the furniture is the drawing's shorthand.

The principle behind the app is that the drawing may be tidied up; the numbers may not. That's why HouseSense never silently guesses a wall further out because a bookcase stood in front of it — it shows what was actually measured. If a whole wall is covered by a fitted wardrobe, the answer is a tape measure — and correcting the room's measurement afterwards with your own figure.