Postcrete calculator
Enter your hole size and post size. The calculator subtracts the post, so you don’t overbuy.
Measuring in feet and inches? Use the US version
Bags needed
29 bags
- Per post
- 3.15 bags
- Total
- 284 litres of concrete
How it works
Each hole’s volume is its area (width² for a square hole, π × radius² for a round one) times its depth. The calculator subtracts the space taken by the post, converts to litres, and divides by the yield printed on the bag.
Example
With number of posts 9, hole shape: square (dug with a spade), hole width 250 mm, hole depth 600 mm, post size: 100 × 100 mm, yield per bag 10 litres, the answer is 29 bags.
Tips before you buy
- A common rule is to bury about a quarter of the post’s length, so a 2.4 m post goes about 600 mm into the ground.
- Put a little gravel in the bottom of each hole so water can drain away from the post.
- Check for buried cables and pipes before you dig.
Common questions
How many bags of postcrete per post?
For a 100 mm post in a 250 mm square hole 600 mm deep, about 3 bags of a 10 litre yield.
How deep should a fence post hole be?
About a quarter of the post’s total length: 600 mm for a 2.4 m post.
How wide should a fence post hole be?
Roughly three times the post’s width, so about 250–300 mm for a 100 mm post.