3.5 inches of clearance is the magic number for cleaning under furniture

If your couch has 3.5 inches of clearance from the floor, you need a robot vacuum that’s under 4 inches tall — otherwise it bonks into the frame and leaves the dust bunnies undisturbed. Most modern robot vacuums hover around 3.5 to 3.8 inches, so measuring your furniture clearance before buying is the difference between a robot that cleans everywhere and one that stops at the sofa’s edge.