On Center (OC)

The spacing between framing members measured from the centre of one to the centre of the next, rather than the gap between them.

Measuring centre to centre rather than edge to edge means the spacing stays consistent regardless of member thickness, and it makes sheet goods land on framing. Sixteen inches on centre divides evenly into a 4-foot sheet three times and an 8-foot sheet six times, which is precisely why it is the residential standard — a sheet of drywall or plywood breaks on a stud at every edge without cutting. Twenty-four inches on centre is permitted for many non-loadbearing and single-storey conditions, uses less lumber, and gives a better whole-wall R-value because there is less thermal bridging through the framing.