“On center” is a construction term that defines the center of a piece of lumber or material, so that measurements can be made from the center of an object to the next.
For example, standard deck joist spacing is 16″ O.C., which means that the distance between the center of one joist to the center of the next should be 16 inches.
This term can also be used when describing the location of any other symmetrical object, like a railing post, joist hanger, footing center, post span, or light location.
