A rug that is too small is the most common living room mistake, and it is easy to see why. People measure the coffee table, buy a rug that fits under it, and end up with a small island floating in the middle of a big room, disconnected from the sofa and chairs. A rug should anchor the seating group, not just cover the floor under the table. This finder works from your room size, your sofa length, and how the furniture sits on the rug, and returns the standard rug size that fits that layout with floor showing around the edges.
The layout choice is the heart of the tool, because it changes the minimum size more than any other input. Front legs on the rug is the most popular arrangement: the sofa front legs and the chair front legs sit on the rug, while the back legs stay on the floor, which grounds the group without needing a huge rug. All legs on the rug is the most generous arrangement and suits large rooms, while the coffee table zone only suits small rooms or a reading corner where the rug is decorative rather than structural.
Here is a worked example with the default inputs. Your room is 5 metres by 4 metres, your sofa is 2.2 metres long, and you choose front legs on the rug. The tool needs a rug at least 2.8 metres long, which is the sofa plus 0.6 metres, and at least 1.6 metres wide for the front-legs layout. Checking standard sizes, 160 by 230 centimetres is too short, while 200 by 290 centimetres meets both needs and fits the room with about 20 centimetres of bare floor on each side, so the recommendation is 200 by 290 centimetres.
That 20-centimetre border of bare floor is deliberate, and it is worth understanding rather than fighting. A rug that runs wall to wall stops looking like a rug and starts looking like fitted carpet, while a rug with a visible floor border frames the seating area and makes the room feel larger. If your room is small, the border can shrink to 10 centimetres, but it should not vanish, because a rug jammed against the walls traps dust at the edges and makes the room feel cramped instead of grounded.
Room shape changes the answer, and the tool handles it by checking both dimensions. A long, narrow room may fit a long rug in one direction but not the other, and rotating a standard rug can solve a fit that looks impossible at first glance. Measure the room in both directions, enter the longer side as the length, and check whether the recommended size fits when rotated. If neither orientation fits, the room is telling you that a smaller layout, such as front legs instead of all legs, is the honest choice for that space.
Sofa length is another number people estimate badly, so measure it rather than guessing. Measure the full outside length, including the arms, not just the seat cushions, because the rug must relate to the whole piece of furniture. A three-seat sofa is often 2.1 to 2.4 metres long, while a corner sofa needs a different approach entirely, since one rug rarely anchors both arms well. For a corner sofa, size the rug to the main seating run and let the return arm sit partly off the rug, or use two rugs with a clear gap between them.
Before you buy, test the size at home with masking tape on the floor. Tape out the recommended rectangle, live with it for a day, and walk around it as you normally would, checking door swings, chair movement, and the path to the sofa. Tape costs almost nothing and reveals problems a screen cannot, such as a rug corner blocking a door or a chair leg catching the edge. If the taped rectangle feels right, order that size with confidence; if it feels wrong, re-run the tool with a different layout and tape that one too.