Most fence posts require anywhere from one to 10 bags of concrete. Actual concrete amounts vary depending on post hole diameter and depth. Account for frost lines and gravel when doing calculations.
Complete calculation:
For reference, a 40-pound bag of concrete typically yields about 0.3 cubic feet, a 50-pound bag yields 0.37 cubic feet, a 60-pound bag yields 0.45 cubic feet, and an 80-pound bag yields 0.6 feet. This means that in the example above, each post would require about eight 50-pound bags.
Mix two 50lb bags of concrete with water in a mixing tub or 5-gallon bucket. Add concrete into the hole and around the 4” x 4”. Depending on your climate, let concrete set up for 24 - 48 hours.
1 – 4 bags of concrete per fence post are typically what's needed. This depends on the type of soil, fence design, height, post size and bag weight. In general the depth of the post's hole needs to be 1/3 to 1/2 of the above ground height of the post.
The depth of the post should be a minimum of ⅓ of the height of what's above ground. This means that if you want a 6-foot tall fence, you need at least 2 feet of the post to go below ground. If this was the case, you would need at least 2 bags of concrete per fence post, with each individual bag being a 50lb bag.
Most fence posts require anywhere from one to 10 bags of concrete. Actual concrete amounts vary depending on post hole diameter and depth. Account for frost lines and gravel when doing calculations.
The depth of the hole should be 1/3-1/2 the post height above ground (i.e., a 6-foot tall fence would require a hole depth of at least 2 feet).
The general rule of thumb when setting a post is that the depth of the post's hole needs to be one-third to one-half of the actual above-ground height of the post. So, a six-foot-high finished post ideally needs to be buried three feet into the ground.
Fast-setting concrete is ideal for setting posts because there's no mixing—you simply pour the dry concrete from the bag right into the hole, then add water.
As a general rule of thumb, you'll need to place at least 1/3 the height of the post in the ground. For example, a six-foot tall fence will need at least two feet of post in the ground.
The answer -— as it often does in fencing construction — depends. As a general rule, Fencing Direct recommends at least a 24-inch footing depth for a 4-foot fence, plus an extra 3 inches for every foot of height (for example, 27 inches for a 5-foot post).
It doesn't matter if it is a do-it-yourself (DIY) project or a professional installation, wood fence or vinyl fence, your fence posts should be set in concrete. Without a properly set concrete footer, your fence posts will begin to sag until they eventually fail.
The American Standards for Testing Materials (ASTM) suggests always setting fence posts in cement. One of the most important reasons your fence posts should be set in concrete is to keep them plumb and level over time.
The 2 ft Rule
Lawsons experts recommend you should dig a hole which has a depth of 2 ft (24 in / 600mm) to ensure you have a stable timber or concrete fence post.
Dig your hole to the correct depth, allowing for the height of the fence panel and the gravel board. As a rough guide the hole should be a minimum 1/3 the height of the fence, so a 6 foot fence would need an 8 foot post in a 2 foot deep hole. Similarly, the hole should be three times the diameter of the post.
A general rule of thumb is to dig the diameter of the hole at least 3-4 times the diameter of the post. For example, if setting 4 x 4 wood posts, dig holes 9-12" in diameter. Posts should be centered in the hole and the posts should always have concrete under them.
Set fence posts or mailbox posts without mixing!
With Fast-Setting Concrete there is no mixing or tools required – You simply pour the dry mix right from the bag into the hole, then add water. Fast-Setting Concrete sets in about 20 minutes so you can quickly move onto the next step of your outdoor project.
An easy way to make a garden path or informal walkway is to simply dump dry concrete on the ground and water it with a water hose. There are a few tricks to making it look good, but it really is a pretty easy way to make a path through the backyard.
Digging fence post holes is easiest with a power earth auger. Check out our article: How to Use a Power Auger. A shovel or spade may take longer, but they're good for cutting overgrown roots in a hole. A digging bar works well for loosening dirt from the sides.
Postsaver® is the number one choice for preventing fence post rot because it will literally block rot. It is a heat-shrinkable outer sleeve that fits over the base of the fence post. The sleeve has a thermoplastic bituminous interior liner, which seals to the wood.
While a treated 4x4 may last 10 to 25 years, depending on the wood, the soil, and weather conditions, following the simple steps below could double or triple that number. By comparison, an untreated wood fence post may need replacing in as little as five years.
To help slow such deterioration, add pea gravel or crushed stone to the bottom of the posthole. Once you have added gravel to a depth of three inches or so, use a piece of scrap lumber to tamp down the layer. Next, pour an additional three inches of gravel into the hole, tamping down a second time.
It's a good question and one that we get asked a lot. For most residential fences 8′ between posts is the maximum. Commercial fences (industrial chain link, for example) typically can handle up to 10′ spacing because of their stronger frames.