Put a room into most size calculators and you'll get something like: furniture covers 34.7%, and 7.775 m² is left. That's accurate. It's also how people end up surprised by how tight a room feels once everything arrives.
7.775 m² is roughly a 2.8 m square. In one piece, that's enough to roll out two yoga mats with room to spare. Empty floor almost never comes in one piece, though.
In this bedroom the empty floor falls into three parts: the area by the door, the space between desk and wardrobe, and a 53 cm gap between the bed and the desk. The calculator adds them all up. But 53 cm is a turn-sideways-and-shuffle gap, and the corner beyond it, by the headboard, is effectively sealed off. It's in the total, and you can't use it.
The spots where a chair rolls back or a wardrobe door swings open are counted as free too. You can't put anything there, yet they inflate the number. The more furniture you add, the more floor gets quietly reserved like this, and the further the calculator drifts from how the room feels.
What I look at instead is the narrowest gap: the tightest spot between two pieces, or between a piece and a wall, and whether it sits on a path you use every day. Here it was 53 cm. Push the bed into the corner, the desk into the opposite corner and the wardrobe down to the bottom wall, and that gap becomes 85 cm. Free floor: still 7.775 m². Not one digit changed, and it's a different room.
The area figures under the planner don't budge however you rearrange things. The route check can flip with a 5 cm nudge. That's a fair hint about which number to watch.