When undertaking a garden fencing project, one of the most common questions homeowners ask is, “How many bags of Postcrete do I need per fence post?” Getting this right is crucial for ensuring the stability and longevity of your fence, so here’s a comprehensive guide to help you through this essential part of your project.

Understanding Postcrete

Firstly, let’s talk about what Postcrete is. Postcrete is a pre-mixed, quick-setting concrete formula specifically designed for securing wooden, concrete, and metal posts. Its ease of use and quick-setting properties make it a favourite among DIY enthusiasts and professional builders alike.

Determining Your Needs

The amount of Postcrete you need will depend on several factors, including the size of the fence posts and the depth and width of the holes they will be set in. While there's no one-size-fits-all answer, there are general guidelines you can follow to estimate your needs.

Standard Fence Posts

For most standard-sized fence posts (around 100mm x 100mm), you will need approximately two bags of Postcrete per post. This estimation is based on the assumption that your post holes are about 600mm deep and approximately three times the width of the post.

Each bag of Postcrete typically covers about 0.01 cubic metres when mixed with water, and a standard hole of the mentioned dimensions has a volume of about 0.02 cubic metres, hence the two bags per post requirement.

Larger Fence Posts

If your fence posts are larger, or if you’re planning to set your posts in a particularly windy or unstable area and decide to dig deeper or wider holes for additional stability, you will naturally need more Postcrete. For posts that are 125mm x 125mm, you might find that two and a half to three bags per post are necessary, especially if your holes are larger than the standard size.

Calculating Exact Amounts

To calculate the number of bags of Postcrete needed for your specific project, you can use the following formula:

  1. Calculate the Volume of the Hole: Multiply the width by the width by the depth of the hole to get its volume in cubic metres. If your hole isn’t a perfect square at the base, just average out the width.
  2. Adjust for the Post Volume: Subtract the volume of the post from the total volume of the hole to determine how much space the Postcrete needs to fill.
  3. Calculate the Number of Bags: Since each bag of Postcrete fills approximately 0.01 cubic metres, divide the adjusted volume by 0.01 to get the number of bags required per post.

Remember, it’s always better to have a little more Postcrete than you estimate needing to accommodate any unforeseen circumstances.

Practical Tips

  • Weather Conditions: Consider the weather conditions when setting your posts. Soggy or overly dry soil may affect the amount of Postcrete required.
  • Follow Instructions: Always follow the mixing and application instructions on the Postcrete bag to ensure optimal results.
  • Quick-Setting: Postcrete sets quickly, so ensure your post is correctly positioned before the mix begins to harden.


Estimating how many bags of Postcrete you need per fence post doesn't have to be a complicated process. By understanding the size and depth of your fence post holes, you can quickly calculate the required amount of Postcrete. Remember, preparation and accuracy are key to a sturdy and lasting fence. Should you have specific concerns or a unique project, consulting with a professional may provide tailored advice suited to your situation. Happy fencing!