There are many different tarps available for purchase online. Tarp covers can range from the lighter grade to medium and heavy-duty. There are also several different varieties of fabrics available including poly, mesh, vinyl and canvas. Despite the grade and fabric composition, every tarp will be constructed as a finished product with grommets. The grommet spacing can be different from one manufacturer to another.
Generally, grommet spacing on tarps will either be every 36", 18" or 12" around the perimeter of the cover. Lighter grade utility tarps will commonly come with grommet spacing every 36". This is due to the fact that utility grade tarps are not used as canopy covers and are made for temporary use and minimal securing. However, heavier grade tarps are made specifically for canopy use and long-term coverage needs. The grommet spacing for these tarps must be closer together to achieve the desired strength and stability.
Heavy-duty tarps usually have grommet spacing that is every 18". Grommets help distribute the tension evenly along the edge of the tarp. The more grommets and closer spacing a tarp has the better the load distribution will be and the longer the tarp will last under severe conditions. 12" grommet spacing on tarps is rare and will usually only be found on the mesh shade tarp variety. Since mesh tarps are commonly used as privacy fabric on fencing, the 12" spacing is required for a secure fit on fence lines.
Deciding on the exact application for your tarps will ditermine the variety that will meet your needs. If you are looking for a longer term coverage solution then the look for outdoor waterproof tarp covers that have a minimum grommet spacing of every 18".