- Concrete Footing Calculator - June 28, 2026
- How to calculate concrete for Post Holes? - June 26, 2026
- How Much Water Do You Actually Need Per Bag of Concrete? - June 18, 2026
📊 Concrete Pier Results
Required Bags (with waste factor)
💡 Pro Tip: Most auger-drilled or excavated pier holes are irregular. Sticking to a 10% waste buffer keeps you from running short on pour day!
Concrete Calculator For Piers: Accurate Estimates for Sonotubes & Footings
When pouring concrete piers for a deck, fence, or structural foundation, getting your material counts right is the difference between a smooth project and an emergency run to the home improvement store.
Our Concrete Pier Calculator eliminates the guesswork. It calculates the exact volume of concrete needed for your project in Cubic Yards, Cubic Meters, and Cubic Feet, while instantly converting those figures into the total number of 80-lb and 60-lb bags you need to buy.
How to Calculate Concrete for Round Piers (The Formula)
If you are using cylindrical cardboard forms like Sonotubes, the math relies on finding the volume of a cylinder. To calculate this manually, you use the following geometric formula:
$$V = \pi \times r^2 \times h$$
- $V$ = Total Volume
- $\pi$ (Pi) = Approximately $3.14159$
- $r$ (Radius) = Half of your pier’s total diameter (e.g., a 12-inch tube has a 6-inch radius)
- $h$ (Height/Depth) = The total depth of the pier hole
Converting to Job-Ready Measurements
Because concrete is ordered in cubic yards but dug in inches and feet, you must convert your measurements:
- To get Cubic Feet ($ft^3$): Convert your radius to feet (inches divided by 12), run the cylinder formula, and multiply by the total number of piers.
- To get Cubic Yards ($yd^3$): Divide your total cubic feet by 27 ($1\text{ yd}^3 = 27\text{ ft}^3$). This is the number you give to a ready-mix delivery truck.
- To get Total Bags: An 80-lb bag of pre-mixed concrete yields roughly $0.60\text{ ft}^3$, while a 60-lb bag yields roughly $0.45\text{ ft}^3$. Divide your total volume with waste by these yields to get your exact bag count.
Quick Reference: 4-Foot Deep Pier Bag Chart
Many structural deck posts must sit at least 4 feet deep to descend safely below local frost lines. Below is a quick-scannable cheat sheet showing how many 80-lb bags are required per pier at this standard depth, including a recommended 10% waste factor.
| Sonotube / Pier Diameter | Volume Per Pier (ft3) | 80-lb Bags Needed (Per Pier) | 60-lb Bags Needed (Per Pier) |
| 8-Inch Pier | $1.40\text{ ft}^3$ | 3 Bags | 4 Bags |
| 10-Inch Pier | $2.18\text{ ft}^3$ | 4 Bags | 6 Bags |
| 12-Inch Pier | $3.14\text{ ft}^3$ | 6 Bags | 8 Bags |
| 16-Inch Pier | $5.59\text{ ft}^3$ | 11 Bags | 14 Bags |
Frequently Asked Questions (FAQ)
How deep should my concrete piers be?
Concrete piers must be poured deep enough to cross your local area’s frost line to prevent the ground from freezing, expanding, and lifting your structure (known as frost heave). In cold climates, this is commonly 36 to 48 inches deep, whereas warmer regions may only require 12 to 24 inches. Always check with your local building department.
Why should I add a waste allowance to my pier calculations?
When you dig a hole using a mechanical auger or a shovel, the walls are never perfectly smooth or perfectly straight. Rocks, loose dirt, and over-excavation around the bottom (belling out) increase the actual volume of the hole. Adding a 10% waste factor ensures you do not run short in the middle of your pour.
How many 80-lb bags of concrete are in a cubic yard?
It takes exactly 45 bags of 80-lb concrete mix to equal one cubic yard ($27\text{ ft}^3$). If you are using 60-lb bags, it requires 60 bags to equal one cubic yard.