How this calculator works
Hole volume = pi x (diameter / 2)^2 x depth. Net volume = hole volume - post volume. Bags = round up(total liters / yield per bag).
Worked example
A 30 cm diameter, 60 cm deep hole with a 10 cm square post needs about 36 L of concrete per hole - 2 bags at 20 L yield.
Assumptions to check
- The hole is a cylinder and the post is square in cross-section, centered in the hole.
- Bag yield must come from the product label; it differs between postcrete-style fast-set mixes and standard premix concrete.
- A post width of 0 models a footing-only hole with no post volume subtracted.