Post Caps come in almost every imaginable color, shape and material. Further complicating the selection process is the enormous number of sizes available and the way the sizes are described. We try to make this as clear as possible so you get the cap you expected the first time. Terms like "Actual" and "Nominal" are used frequently. Much like a 2x4 is actually 3-1/2" x 1-1/2" in size, post cap manufacturers do the same thing, but to mix it up some manufacturers of Composite or PVC post sleeves only use actual sizes in their description. As a general rule if you select a post cap from the same manufacturer as the post sleeve you're likely going to get the proper cap. Manufacturers want you to use their products so they might change the shape slightly (Rounding or projecting corners) so only their caps will fit.
Measuring a post to determine what size post cap you need is pretty simple and all you need to do is get a measuring tap and stretch it over the top of the post. The measurement you get will determine what interior dimensions the post cap you purchase should be. Here is an example we made to show you how to do this.