Definition
On-center (OC) spacing refers to the measurement from the center of one structural member to the center of the next, such as studs, joists, rafters, or trusses. OC spacing is the standard method for specifying framing layout. Common OC spacings include 12 inches (heavy loads, tile floors), 16 inches (standard residential), and 24 inches (decks, roofs, non-load bearing). The measurement is taken from the center of each member, not the edges.
Formula
To calculate the number of studs needed for a wall at 16 inches OC: For a 96-inch wall, (96 / 16) + 1 = 7 studs. This includes the starting stud and adds one for each complete space. Always add extra for corners, intersections, and waste (typically 10-15%).
Example
Stud Layout Example
For a 12-foot (144-inch) wall at 16 inches OC: 144 / 16 = 9 spaces, requiring 10 studs. Add 2 studs for each corner (4 total) and 1 for each intersection with perpendicular walls. For a simple rectangular room, order approximately 15-20% more than the basic calculation to account for corners, windows, doors, and waste.