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:
- (L) Length of Spread. Length over which the objects are evenly distributed (e.g., a fence that is 240 feet long)
- (n) Number of Objects. The numbeer of objects being evenly spread over the distance (e.g., 31 posts)
On Center Spacing (oC): The calculator returns the even separation in inches or feet. However, this can be automatically converted to other length units (e.g. yards or meters) via the pull down menu.
The Math / Science
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)
where:
- oC = on center spacing
- L = length
- n = number of objects
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
