Garden fence post hole circumference and tool question - Do I have this right?

[reoreborn85]

I'm so sorry if this has been anwsered. I have looked but most questions seem to be with 5ft fence posts or have other contributing factors than mine.

I am putting up 6 foot fence panels using 8ft concrete fence posts (10cmx10cm.) I currently have a normal spade and a post hole digger.

From what i understand I need to have 2ft of the post under ground.

Every video/advice site I find have totally different suggestions and it's throwing me off lol One site says the hole should be slightly wider than the post while others say at LEAST x3 the dimensions of the post.

Question 1: Maybe I'm over thinking this but how big (circumference) should the hole be? I see some people saying the posts dimension x3 (so width and depth 30cm). Is this correct?
Question 2: Should the hole be squared off fully? I have seen some people saying the walls of the hole should be fully flat while others saying a bit raggedy are fine?
Question 3: going by the 30x30cm hole dimension will one bag of postcrete be enough for each hole OR should I go with two per hole?

 

[freddiemercurystwin]

Post size x 3 seems about right, as neat as you can be bothered to make it, it won't make any difference, assume 2 bags per post, you'll know after the first post for sure but always better to have more than you need, you can always return any unopened bags.

 

[JohnD]

Is the soil soft and wet? If so, I find you need more width on the lee side or the post can push through it in strong winds.

I live in a coastal area so this may be less common for you.

Beat the soil down hard after the concrete has set, to compress and consolidate it.

For elegance, you do not need a big block showing at the surface. You can make a wooden formwork collar so the last few inches are a neat square a few inches bigger than the post, slightly trowelled to throw off rain. I also set the concrete gravel boards into the top of the concrete to prevent them shifting.

BTW postcrete is not as strong as regular concrete (and is more expensive) but it's up to you.