Hole Volume Calculator
Concrete needed to fill round post holes.
Estimate concrete to set fence or deck posts in round holes.
How the Math Works
The Hole Volume Calculator uses the standard formula for calculating the volume of a cylinder: V = πr²h. Since we're given the diameter instead of radius, the formula becomes V = π(d/2)²·depth·holes. This means we take half the diameter to get the radius, square it, multiply by pi (approximately 3.14159), then multiply by the depth of each hole. Finally, we multiply by the total number of holes to find the combined volume of concrete needed for all post holes.
Practical Applications
To use this calculator practically, simply measure the diameter of each post hole in inches or centimeters, determine how deep you need to set your post (typically 1/3 of the post height above ground), and count how many holes you need to fill. For example, if you're installing 4 fence posts in 8-inch diameter holes that are 24 inches deep, plug these numbers into the calculator to find you'll need approximately 4.19 cubic feet of concrete.
Day-to-Day Use
This calculator saves you time, money, and trips to the hardware store when doing DIY projects around your home. Whether you're building a fence, installing a deck, setting mailbox posts, or constructing a gazebo, knowing exactly how much concrete to purchase prevents costly overbuying and ensures you won't run out mid-project. It also helps you estimate costs before visiting the supplier, making your home improvement projects more efficient and budget-friendly.
Worked example
6 holes, 10 in across, 3 ft deep → ~9.8 ft³.
FAQ
Subtract the post?
For accuracy, subtract the post's buried volume; ignoring it adds a small safety margin.