To DIY you figure out your linear feet and do the math according to the type of boards you are using. To figure out how much it would cost to have someone else do it, call HD and various contractors to get some quotes. NextDoor is a better place for this question, unless you meant to Google an answer rather than post to a specific HD location.
You need to decide if you're going board on board, side by side, or any of the other options there are. Also do you want 4" or 6" wide pickets? Dog-eared or no? How tall? 6 ft? 8 ft? 10 ft? The height depicts alot of things like how long of posts you need and how many. The taller you get not only do the pickets get taller with it, but the posts have to be set closer together. Also, what type of material? Pine or cedar? Pre-stained or not? A lot of things you should have made up in your mind before you get prices. Because everyone is going to ask you those same questions. I dont work for Home Depot nor do I represent their company, just an avid customer/contractor. Good luck
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