Concrete planning tool
Concrete Post Hole Calculator
Estimate the concrete volume required to fill one or more identical cylindrical post holes. Enter the hole dimensions, quantity, and optional waste allowance.
Post hole dimensions
Enter the dimensions of the holes
Waste allowance is added to the concrete volume and shown separately in the estimate.
Concrete required
Concrete volume for the specified holes
Concrete required
0.52yd³
- Volume per hole
- 2.36 ft³
- Before waste
- 14.14 ft³
- Waste allowance
- 0.00 ft³
- Including waste
- 14.14 ft³
Live diagram
Post hole visualization
Diagram shows relative proportions, not scale.
How it works
From post hole dimensions to concrete volume
The calculator treats every hole as an identical cylinder, calculates the volume of one hole, multiplies by the number of holes, and applies your waste allowance.
Concrete post hole formula
Radius equals diameter divided by two. The volume of one cylindrical hole is:
V = πr²h
Total = volume per hole × number of holes × (1 + waste percentage ÷ 100)
Worked example: 6 holes × 12 in diameter × 36 in deep
- Convert diameter and find radius12 in = 1 ft; radius = 0.5 ft
- Convert depth36 in = 3 ft
- Volume per holeπ × 0.5² × 3 ≈ 2.36 ft³
- Six holes2.356… × 6 ≈ 14.14 ft³
- Convert to cubic yards14.137… ÷ 27 ≈ 0.52 yd³
Understanding diameter and radius
Measure the hole across its widest point to enter diameter. The calculator divides that measurement by two to obtain radius for the cylinder formula.
Calculating multiple holes
All holes in one calculation are assumed to have identical diameter and depth. For different sizes, calculate each group separately.
Understanding waste allowance
Waste is applied after calculating the base volume for all holes. Enter the percentage appropriate for your project; no universal allowance is assumed.
US and Metric units
US Customary mode accepts diameter in inches and depth in inches or feet. Metric mode accepts diameter in centimeters and depth in centimeters or meters. Switching systems preserves the same physical project.
Estimate limitations
This estimate assumes identical cylindrical holes and calculates their full excavated volume. It does not subtract post volume, automatically account for irregular excavation, or determine appropriate diameter, depth, frost depth, structural adequacy, or code compliance.
Use local code, manufacturer instructions, and qualified professional guidance where required.
Frequently asked questions
- How do I calculate concrete for a post hole?
- Use π × radius² × depth, then multiply by the number of identical holes.
- Why does the calculator ask for diameter instead of radius?
- Diameter is commonly measured across the opening; the calculator divides it by two internally.
- Does the calculator subtract the post volume?
- No. It calculates the full excavated hole volume and does not show a post in the diagram.
- Should I add waste?
- Use the waste allowance that fits your project conditions; the calculator does not prescribe one.
- Can I use feet instead of inches for hole depth?
- Yes. Select feet from the native depth unit control in US Customary mode.
- Can I use Metric measurements?
- Yes. Metric mode supports centimeters and meters while preserving the same physical project.
- Does this calculator tell me how deep a fence post should be?
- No. It estimates volume only and does not determine suitable post depth or structural requirements.
- How do I calculate how many concrete bags I need?
- Use this calculator to determine volume, then enter that volume and the product’s listed yield in the Concrete Bag Calculator.