To find how much fencing you need, it’s essential to either contact a pro or follow these general steps: Determine code restrictions like the height, post spacing, etc. Find your property lines, utility lines, and where you’d like the fence located. Measure the distance where the fence will be. Divide that measure by the post spacing, then add two. This is how many posts you’ll need. Multiply that figure by two or three for rails. Divide the total length by the width of your pickets when calculating how much wood you’ll need.