Image: Urban Barn
It's true that most people have rugs that are too small. My guess is that 5' x 7' rugs are readily available and more affordable than 8' x 10', so they're easier to bring home and try out. Most bedrooms and living rooms need an 8' x 10' or 9' x 12' which aren't easy to sling home, but the result is so worth it.
Everyone loves guidelines, so here are my go-to rules for getting the right size rug:
1. Measure your sofa and add 16"
You want to have at least 8" of rug visible on each side the sofa. If you have a side table, add that to the measurement so the table is sitting entirely on the rug.
2. The rug should sit at least halfway under the sofa
I'm not a fan of just the front legs perched on the edge of the rug. It should go to the mid-point of the sofa's seat depth.
3. In an open concept room all the furniture sits on the rug
If your sofa is against a wall point #2 is a good guide, but in an open plan room where no furniture is against the walls, you want to define the seating area by having all the furniture on the rug.
Illustrating guideline #1, it's important to measure at least 6" on each side of the sofa. You need more if you have a side table. The entire table should fit on the rug or be entirely off the rug.
#2 . When your sofa is against a wall the rug should be about halfway back.
#3 in action. A rug large enough to accommodate all the furniture looks right in an open plan room.
Breaking the rules...or solving problems
I've fallen for a vintage rug once or twice, and they tend to be odd sizes or smaller sizes . But when you like something you find a way to make it work. If you're stuck with a too-small or non-traditional sized antique rug - and you love it - there are options. If you don't love it, don't invest any more of your time, money or emotional capital into keeping it. Don't succumb to the sunk cost fallacy. Find a good place to donate it and get yourself the rug of your dreams.
Solution #1 Layer
Layering a too-small rug that you love with a right-sized rug is a great solution I've found they shift around a bit, especially with kids in the house, so lay an anti-slip mat or use carpet tape if that won't damage either rug.
Solution #2 Mix two small rugs
I love how interesting and unexpected this looks. It's a great move if you have two 5' x 7' rugs.
Solution #3 repurpose
This will only work with lighter weight rugs like kilims and flat weaves. Chairs, benches, ottomans and poofs can be readily upholstered using an old beloved rug. If you can't bear to have it cut up, consider a smaller rug as a wall hanging. They can be used in place of a headboard in a casual, boho-style bedroom.
Solution #4 Relocate it
If you love the rug find a new room for it. - but make sure it's the right size for the job!