The On Center Spacing calculator computes the even spacing between a number (n) of objects (e.g. posts, studs, joists, rafters, trusses, lights, rebars) over a specified length (L) or distance.
INSTRUCTIONS: Choose units and enter the following:
On Center Spacing (oC): The calculator returns the even separation in inches. However, this can be automatically converted to other length units (e.g. feet or meters) via the pull down menu.
The on center calculation is fairly easy. However, people typically fail to account for the first object. So, if you want to spread 4 posts (n) out to create a fence 24 feet long (L), you can not spread them out where spread = 24 ft/4. This forgets that the first post is at position zero. You a have to reduce the number of posts by one for the first post. In this case, the calculation would be 24 ft/3 (3 = n-1), which 8 ft separation. The formula for on center spacing is
oC = L / (n-1)
Many applications of spacing can be seen in life. Four common spacing examples are fences, floor joist, the spacing of studs and the spacing of rebar in a slab.
Spacing of joists
Spacing of studs
Spacing of rebar