Remove the double-sided wood screw from the old leg by placing a wrench onto the square section of the screw and then by turning the screw out of the leg. If you do not have the old leg or the screw is missing, select a double-sided wood screw that measures slightly larger than the screw hole in the underside of the couch.
Measure the length of an existing leg with a tape measure. If you are replacing all four legs, make a decision on how tall you want the legs. A length of 4 to 5 inches is usually plenty.
Cut the leg out of a wooden down rod. Select a dowel rod that closely matches the diameter of the existing legs. if replacing all four legs, use a rod that measures between 2 and 3 inches in diameter. Use a miter saw to make the cut. A miter saw makes a straight cut and allows for accuracy if you make more than one leg.
Drill a hole through the top center of the leg with a hand drill and drill bit that measures half the diameter of the double-sided wood screw.
Thread the wood screw into the hole with the wrench.
Stick the tip of the exposed screw into the hole on the underside of the couch and then thread the screw into the couch by turning the wood leg. Do this until the wood leg rests against the underside of the couch.