Measure the path, not only the wall
A sofa can fit against a wall and still make the room hard to live in. Check walkways, closet doors, drawers, and balcony doors.
Compare the outer furniture dimensions with an empty rectangular room in two orientations. The calculation reserves clearance along both sides parallel to the furniture length and at one end. Check doors, other furniture and the complete walking route separately.
A sofa can fit against a wall and still make the room hard to live in. Check walkways, closet doors, drawers, and balcony doors.
Depth is where many online furniture mistakes happen. A deep sofa or chair can consume more floor space than the listing photo suggests.
Use painter's tape or boxes to mark the item on the floor. Walk around it for a day before ordering anything hard to return.
Measurements catch obvious fit problems. A room photo helps with softer decisions: whether the item feels too heavy, blocks the flow, or matches the space.