How many bags of Postcrete per post?
Use the Postcrete calculator to get the exact number from the manufacturer's table. This guide explains how it works.
It depends on three things
- Post size: Round 5cm, Square 7.5cm, or Square 10cm
- Hole width: sizes listed in the Tarmac table (15–30cm)
- Hole depth: sizes listed in the Tarmac table (30–75cm)
Example: Square 10cm posts
For a common fence post (square 10cm) in a 30cm × 60cm hole, the Tarmac Blue Circle table says 2 bags per post. If you're installing 6 posts, that's 12 bags total.
Why not just use a formula?
Postcrete isn't a constant yield per bag — the manufacturer provides a lookup table based on tested combinations. Always use the table rather than calculating from volume.
How deep should the hole be?
Tarmac's guidance: dig a hole three times wider than the post and as deep as 1/3 of the fence height above ground. For a 1.8m fence, that's roughly 60cm deep.
What is Postcrete for?
Postcrete is a ready-to-use mix sold for setting fence and similar posts. Check the current Tarmac Blue Circle technical sheet for conditions of use before you rely on it for gates or anything heavier than a domestic fence post.
Can I use regular bagged concrete instead?
Yes. Use the concrete calculator in round-hole mode for volume and bag counts. Postcrete is a lookup table, not a volume yield — do not convert the table into a m³-per-bag figure.
Calculate Postcrete bags
Select your post size and hole dimensions to get the number of bags from the official table:
Use Postcrete calculatorSource: Tarmac Blue Circle Postcrete technical information (SVD1223), read 26 October 2026.