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What is the correct post hole depth for a deck?

Just Starting Out

What is the correct post hole depth for a deck?

i have an area of 2.4 x 4.4 at 300mm height above the ground to build a deck what is the minimum for post hole depth to be dug or the formula please  

Kind of a Big Deal

Re: Post hole depth for deck

General rule of thumb is 1/3 to 1/2 the length and the width to be 3X the post.

A lot depends on what your soil type is, I tend to go at least 300mm for post depth to be on the safe side.

Bunnings Team Member
Bunnings Team Member

Re: post hole depth

Hello @eddy


Welcome to the Bunnings Workshop community. Thank you for joining us and sharing your question about post-hole depth for your deck.


It's great that you've received excellent advice from @Brad. I totally agree with his suggestion of at least 1/2 the length or more. I subscribe to over-engineering and would probably go past the 300mm as well for safety. Would it be possible for you to post a photo of your plan? It would give us an idea of the layout and provide you with a comprehensive recommendation. It sounds like a fantastic project, any updates you can provide while building the deck would be much appreciated.


If you need more advice or information, please let us know.




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Re: post hole depth


I came across this post for the preparation for the creation of a Bathhouse on a deck.

Does this rule apply for strirup posts as well? 

i.e The overall size of the deck is 2400 x 2100mm

I plan to use 3 bearers with metal strirup posts at end and one in the middle

thus 9 posts.

The drop across the ground is 300mm max at one end only (sloped ground)

Plan to use double joists under the bathtub, located on one side of the flooring

and 900mm x 2400mm toungue and groove flooring

So if i used the 600mm posts, that would put it 300mm in the ground at one end.

Appreciate any feedback.

PeterOverall Deck Slope.jpgOverall Layout Deck.jpg



Re: post hole depth

Welcome to the Bunnings Workshop community @Peter1960. It's great to have you join us, and many thanks for your question about installing posts.


That will work. 300mm in the ground for 600mm supports would typically be fine. However, the depth and size of the footer will be governed by the soil type in your area and the weight each post bears. In order to work that out, you'd likely need to get the structure engineered and reference soil analysis reports for the area.


Please let me know if you have any questions.




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Re: post hole depth

Much appreciated Mitchell.

Shall do.

Thank you


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