How the rug size is worked out
Measure the room wall to wall, then the furniture the rug has to hold. The floor border is the bare floor you want to see between rug and walls: designers quoted by Homes & Gardens leave 8 to 24 inches, and a Belgian rug retailer suggests 20 to 30 cm. The room minus that border on each side is the largest rug that fits.
Living room: the rug should be wider than the sofa. With front legs on, it starts about 20 cm (8 in) under the front of the sofa and runs to the far edge of the seating area. With all on the rug, it also runs behind the sofa, which suits sofas with a solid base.
Dining: leave at least 60 cm (24 in) of rug beyond the table on every side, so the back legs stay on the rug when a chair is pulled out.
Bedroom: rugs run across the bed. Allow at least 45–50 cm (18 in) beyond each side and the foot so you step onto rug, not floor. The lower two-thirds placement starts in front of the bedside tables; a whole-bed rug sits under them too.
The result lists the smallest standard size that covers the layout and still keeps your border, in feet or centimetres. Example: a 220 cm sofa with 170 cm of seating in front needs at least 250 × 190 cm; in a 5 × 4 m room the first standard size that works is 200 × 290 cm.