We get asked this question a lot. It’s a good thing to know when buying your concrete. There is nothing worse than getting to your last two posts and coming up a bag short. It’s never good when the folks at the home center know you by first name by the end of the weekend.
The number of concrete bags required will vary based on the size and length of post being buried. You can find concrete calculators online to help determine how many bags you will need. Simply type something along the lines of ‘Concrete Calculator Fence Posts’ and you will get multiple hits. Most Concrete producers have one on their website.
To use the calculators, you will need to know the following:
- Size of your posts
- Diameter of the hole (usually 3x the post size)
- Depth of the hole
- Number of posts
The size of your post will be on your quote or invoice. For most fences, its going to be between 2in, 2.5in or 3in. Take that post size and multiply it by 3 to get the post hole width.
The depth to dig your post hole varies by region. Rule of thumb is that in dry areas with no winter freeze, you should set the post 18” to 24” in ground. In areas with heavy winter and persistent freeze, you should set them 24” to 36” in ground. To determine how much post you need above ground vs buried in ground (your post depth), take the following into consideration:
- The height of your fence panels
- How much of a gap you want under each panel for grass trimming/ landscaping (ideally 2-3”)
- Where you want your post caps in relation to the top of the fence panels
NOTE – If you have a fence panel style with finial tips sticking through the top, we recommend installing the fence so that the tips of the fence panel line up with the top of the post WITHOUT the post cap on.
- EXAMPLE – Let’s say we have a 4’ tall fence panel style with finial tips on top, 7’ long posts and we want a 2” gap at the bottom of the fence. You would set your post so that 4’2” was sticking up above ground and your post hole was 2’10” deep (4’2” above ground + 2’10” buried = 7’ post length).
NOTE – If you have a flat top style fence panel, we recommend setting the top rail at least an inch below the top of the post so you have room for your brackets and post cap.
- EXAMPLE – Let’s say we have a 4’ tall fence with a flat top style, 7’ long posts and we want a 2” gap at the bottom. You would set your post so that 4’3” was sticking up above ground and your post hole was 2’9” deep (4’3” above ground + 2’9” buried = 7’ post length). That way we can have the 2” gap at the bottom of the panel and the 1” gap from the top of the post.
You can choose to have the posts stick up higher or inline with the fence tips matching the height with the post cap attached. Simply adjust the example calculations above to match up with your desired look.
Lastly, the number of posts on your quote or invoice will tell you the number of post holes.
Enter that information into the calculator. The typically come back in the number of 40lb, 50lb, 60lb, 80lb or 90lb bags you would need.
Math not your thing or have any questions about the info above? Give us a call (800-261-2729) or shoot us an email ([email protected]). We would be happy to help answer any questions!