How to Determine Posts Needed to Build a Fence

Ready for some calculations? Building a fence is all about the math. When it comes to determining the number of posts you will need to build your fence, you will need to know the size of your space, the materials allowed and a calculator to tackle the math. Luckily, there is plenty of expert advice on fence building available from both contractors, do-it-yourselfers and home improvement sites. Online fencing calculators are available for exact measurements and materials if you prefer to skip the math problems.

Man erecting a wooden fence outdoors
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How to Determine Posts Needed to Build a Fence

Fencing Materials and Post Size

The materials you use for your fence can help determine the posts needed. Vinyl, wrought iron and some wooden fencing will come in panels and may need partial panels to complete the project. Your posts will be round or square depending on the materials. The width of the post is also determined by the height of the fence. The needs of a chain link fence are different from the needs of a 6-foot vinyl privacy fence. Have an idea of what kind of material you want to use. This saves a bit of calculating down the line. When you know the size of the yard, plus the width of the post, you can determine the number of posts.

Post Placement

The key rule of thumb: Posts are set around 6 to 8 feet apart. Unless you have HOA restrictions, local land regulations or a smaller yard, this is the basic standard for post measurement. Do not place your posts farther than 8 feet apart because the fence may sag over time. Measure the length of your yard. This will be your fence length. The number of posts you will need is your fence length divided by 6 or 8. For example, a yard of 100 feet with 8-foot placement will require around 13 posts. Take your gate into consideration as well. An even number of 14 posts will probably be needed for the gate to be secured.

Post Height

Your post heights will be determined by the height of the fence. They must be as high as the top horizontal railing. The post will be partially buried, so take this into consideration when purchasing. The height of your post multiplied by the number of posts will equal the number of feet of post material needed. At least 33 percent (or 1/3) of the fence post will need to be buried. A 4-foot iron fence will need to be secured in a 2-feet deep hole. This means that your post will have to be at least 6-feet long to be installed correctly. For a 6-foot tall vinyl privacy fence, your posts will need to be 9-feet long. Another fun calculation: Subtract the amount of feet of the gate from the fence footage to determine the linear number of fence footage. Divide this number by the preset panel length to calculate the number of fence panels needed between your posts.