Know what fits
before you buy it.

Thirty-six inches for a main route, 30 inches for a secondary path between furniture, and 24 inches only where one person passes occasionally. Hallways are built at 36 inches for exactly this reason. Measure to the furniture rather than the wall, because a sofa arm is what you actually hit.

Measure wall to wall at floor level, then record every door swing, window sill height, radiator and vent, since those are what shrink the usable rectangle. Note the ceiling height as well. Then tape each piece's footprint onto the floor in painter's tape before you order anything.

Compare the sofa's diagonal depth, measured from the top of the back to the front of the base, against the door opening. Interior doors are usually 30 to 32 inches and front doors 36. If that diagonal is smaller than the opening, the sofa goes through on its side.

Thirty to 36 inches above the tabletop, measured to the bottom of the fixture, and add 3 inches for every foot of ceiling above 8 feet. The fixture should span about half to two-thirds of the table width, and it centers on the table rather than the room when the two disagree.

A bedroom door is usually 30 inches, a main interior door 32 inches, and an entry door 36 inches, all of them 80 inches tall. The clear opening measures about 2 inches less than the nominal size once the slab and stops are in place, which is what matters when moving furniture.

Draw every door swing first, then treat the leftover shape as the real room. The largest piece goes on the longest uninterrupted wall segment, and the lanes between doors become 30-inch corridors that nothing crosses. Floating a sofa with its back to a doorway is often the only way to reclaim a corner.

The sofa first. It sets the scale of the room, its color is far harder to match than a rug's, and the rug size depends on where the seating finally lands. Choose the rug once you know the sofa's length, depth and position, not before.

Work at a scale of one graph-paper square per foot: outline the room, mark doors, windows and outlets, then cut furniture footprints to the same scale and slide them around. Ten minutes of paper saves a weekend of dragging. Check every walkway against the 30-inch rule before committing.