Last modified by KurtHeckman on 2017/03/07 17:58
Equations in "On Center Calc Collection"
On Center - Count On Center - Total Length
On Center Spacing

The On Center calculator computes the three components of on-center spacing:

  • On Center Count:  This is the number (n) of objects that can be evenly spaced. 
  • On Center Spacing: This is the on center spacing (oC). 
  • On Center Total Length: This is the total length (L) of the group of objects. On Center Uses300px-Westtown.jpgFencesi-joist.pngFloor Joistsframed wall.jpgWall Studs slab 1.pngRebar Mats


On center spacing is used in many applications including:

  • Fences, where fence posts are evenly spaced, and fence rails or wires are evenly spaced.
  • Framing, where studs, joists, rafters, trusses are evenly spaced.   For example, studs in a wall are typically space every 16".
  • Rebar, where the grid of rebar (mats) are evenly spaced reinforcement bars.

The Math

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.



  • On Center - Count by vCalc
  • On Center - Total Length by vCalc
  • On Center Spacing by vCalc