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Material Calculator Guides
How Many Bags of Postcrete Per Fence Post?
How many bags of postcrete will you need for each fence post? If you’re installing a standard garden fence, two 20kg bags of our Coarse Insta Post Mix per fence post is the usual figure for a fence post set around 600mm into the ground, and it’s the amount our fence calculator allows for. A larger hole, a taller post, or softer ground conditions may require three bags instead. Gate posts should always be concreted in and will typically use the same two 20kg bags per post as a minimum.
Example: An 18m straight run of 6ft fence with concrete slotted posts takes 10 panels and 11 posts. At two bags a post that is 22 bags. Add a single gate on the same run and its two gate posts take another 4 bags.
Why Two Bags Is Usually Enough
A standard fence post hole is often around 250-300mm wide and 600mm deep. This gives enough room for a concrete surround that holds the post securely while still being economical on materials.
Most professional fence installers work on the basis that:
- One 20kg bag is rarely enough for a full-depth fence post hole but would be okay for a small sign post not holding any weight.
- Two 20kg bags provide a solid concrete footing for the majority of garden fences.
- Three bags are reserved for larger posts, deeper holes, or poor ground conditions.
Using the correct amount of postcrete helps prevent posts from loosening, leaning, or moving during high winds.
When You Might Need Three Bags
Some installations require more than the standard two bags.
You may need three 20kg bags per post if:
- The fence is over 1.8m tall.
- The post hole is deeper than 600mm.
- Ground conditions are very soft or sandy.
- The site is particularly exposed to high winds.
- You are using larger section posts, 150mm x 150mm or above.
In these situations, the larger concrete footing provides additional stability and resistance to movement.
How Much Post Mix for Gate Posts?
Gate posts carry significantly more load than ordinary fence posts because they must support the weight and movement of the gate.
For this reason:
- A deeper or wider hole is often recommended.
- Two bags is generally considered the minimum. (As is allowed in our fence calculator with the option to add extra bags.)
- Three bags may be advisable for heavy timber or driveway gates.
Taking shortcuts on gate post foundations is one of the most common causes of sagging gates over time.
Postcrete vs Traditional Concrete
Postcrete is popular because:
- Sets Quickly.
- No pre-mixing required.
- Reduces installation time.
- Requires less equipment than traditional concrete on site.
For most residential fencing projects, postmix provides a convenient and reliable method of securing fence posts. Check out our full guide on The Difference Between Postcrete and Concrete.
Calculating Postcrete Requirements for a Fence
| Posts in Fence Line | Bags of Post Mix (2 per post) | Cost inc Vat (£5.32 each*) |
|---|---|---|
| 5 | 10 | £53.20* |
| 8 | 16 | £85.12* |
| 11 | 22 | £117.04* |
| 14 | 28 | £148.96* |
| One Gate = 2 Gate Posts | 4 (Minimum) | £21.28* |
*Price correct at time of publication. To see the price of post mix today, check out our post mix here.
Top Tip: Always allow for a couple of extra bags on site, as you never know when you will need to make a hole bigger than expected.
To estimate the total number of bags needed, multiply the number of fence posts by the number of bags required per post. Use our fencing calculator to take the manual work out of estimating the number of panels, posts and post mix you need for your job. Please note our calculator is used for estimates and final quantities may need checking with a professional installer.
Coarse Insta Post Mix 20kg
A waterproof 20kg bag of ready to use postcrete, just add water to the mix and set your posts into the ground.
FAQ’s
Can I use just one bag of postcrete?
For a full depth fence post installation, one bag is usually insufficient. Most standard fence posts require around two 20kg bags to create an adequately sized concrete footing.
Do I need to add water?
Yes, simply add water into your post hole, and pour the postcrete evenly around the post until no standing water remains. No need to pre-mix anything beforehand.
How long does postcrete take to set?
Postcrete is rapid setting meaning it will begin to harden in 5-10 minutes. This gives you enough time to ensure the post is in the correct position and plumb. After the initial 10 minutes it will continue to set harder over the next hour, at which point it will have reached a state in which it has cured enough for you to start hanging fence panels or attaching rails.
