According to the water sports supply company West Marine, oars should be one-half the distance between the oarlocks times three, plus six inches. Boats that are unusually narrow require shorter oars.
If the space between the oarlocks is four feet, the equation begins with half that distance, which is 2 feet, times three, which equals 6 feet. Add six inches to that, and each oar should be 6 feet 6 inches long. Correct oar length is crucial. Oars that are too long do not rise out of the water enough, while oars that are too short do not have enough material in the water to allow the rower to pull properly.