The Objects Spacing Calculator computes the three components of on-center, evenly spaced objects:

• Number of Evenly Spaced Objects:  This is the number (n) of objects that can be evenly spaced. 
• On Center Spacing: This is the on center spacing (oC) for even distribution over a length or distance.
• Length Spanned by Evenly Spaced Objects: This is the total length (L) of the group of objects. On Center UsesFencesFloor JoistsWall Studs Rebar Mats
• Ideal Spacing below Max: Computes the ideal even spacing of objects across a length below a max spacing, where the max spacing is the "No Greater Than" spacing value.

Application

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.