Enter the hole size, post size, and number of holes to calculate concrete volume, bags, and cost.
How to Use the Post Hole Concrete Calculator
Enter the hole's diameter and depth, pick round or square for the post shape, and give its size. The post's own volume is subtracted from the hole before the bag math runs, and the number of holes multiplies the whole result at once.
A post sitting in a hole displaces concrete — ignore that and you'll over-order. This calculator treats the hole as a cylinder and the post as either a smaller cylinder or a square prism, subtracting one from the other:
net volume = [π × (hole diameter ÷ 2)² × depth − post cross-section × depth] × number of holes × (1 + waste %)Setting post size to 0 treats it as an empty hole — useful if you're filling a footing hole with no post going in it, like a mailbox base or a simple concrete pier. Round posts (fence posts, most mailbox posts) and square posts (many deck and structural posts) use slightly different cross-section math, which is why the shape toggle is there rather than a single generic post-width field.