🕳️ Post Hole Calculator
Calculate concrete needed for post holes
Hole should be 2-3× post diameter
Standard depth: 1/3 of post height above ground
How to Use This Calculator
Select Post Size
Choose your post diameter: 4 inches (4×4 post), 6 inches (6×6 post), or 8 inches (8×8 post). This helps determine appropriate hole size.
Specify Hole Dimensions
Select hole diameter (should be 2-3× post diameter, standard is 12 inches) and depth (standard is 24 inches, or 1/3 of post height above ground).
Enter Number of Posts
Input the number of post holes you need. The calculator will multiply the volume per hole by the number of posts to get total concrete needed.
Calculate and Order
Click "Calculate Post Holes" to see concrete needed in cubic yards, cubic feet, and bags. Add 10% extra for waste and order concrete accordingly.
Formula
Volume per Hole (cubic feet) = π × (Hole Radius)² × Hole Depth
Hole Radius (feet) = Hole Diameter (inches) ÷ 2 ÷ 12
Hole Depth (feet) = Hole Depth (inches) ÷ 12
Total Volume = Volume per Hole × Number of Posts
Cubic Yards = Total Volume (cubic feet) ÷ 27
Example 1: Standard Fence Post (4×4 post, 12" hole, 24" deep)
Step 1: Calculate hole radius: 12" ÷ 2 ÷ 12 = 0.5 feet
Step 2: Calculate depth: 24" ÷ 12 = 2 feet
Step 3: Calculate volume: π × 0.5² × 2 = π × 0.25 × 2 = 1.57 cubic feet per hole
Step 4: For 10 posts: 1.57 × 10 = 15.7 cubic feet
Step 5: Convert to yards: 15.7 ÷ 27 = 0.58 cubic yards
Step 6: Calculate bags: 15.7 ÷ 0.6 = 27 bags (80 lb each)
Example 2: Deck Post (6×6 post, 14" hole, 36" deep)
Step 1: Calculate hole radius: 14" ÷ 2 ÷ 12 = 0.583 feet
Step 2: Calculate depth: 36" ÷ 12 = 3 feet
Step 3: Calculate volume: π × 0.583² × 3 = 3.21 cubic feet per hole
Step 4: For 4 posts: 3.21 × 4 = 12.84 cubic feet
Step 5: Convert to yards: 12.84 ÷ 27 = 0.48 cubic yards
About Post Hole Calculator
The Post Hole Calculator is an essential tool for homeowners, contractors, builders, and DIY enthusiasts who need to accurately determine how much concrete is required for fence posts, deck posts, or other post holes. This calculator eliminates guesswork by providing precise concrete volume calculations based on post size, hole diameter, and depth, helping you order the right amount of concrete without waste or shortages.
When to Use This Calculator
- Fence Post Installation: Calculate concrete needed for fence posts, gate posts, or privacy fence posts
- Deck Post Installation: Determine concrete quantities for deck posts or porch posts
- Mailbox Post: Estimate concrete for mailbox post installation
- Sign Post: Calculate concrete needed for sign posts or light posts
- Budget Planning: Calculate material costs by determining exact concrete quantities needed
Why Use Our Calculator?
- ✅ Accurate Volume: Precise calculations prevent over-ordering or running short
- ✅ Multiple Units: Shows results in cubic yards (for delivery), cubic feet, cubic meters, and bags
- ✅ Bag Calculations: Provides bag counts for both 80-pound and 60-pound bags
- ✅ Multiple Posts: Calculates total concrete for any number of posts
- ✅ Cost Planning: Helps budget accurately by determining exact material needs
- ✅ Time Savings: Instant calculations eliminate manual math and measurements
Common Applications
Fence Posts: Homeowners and contractors planning fence installations use this calculator to order the correct quantity of concrete for fence posts. Standard fence posts use 4×4 posts in 12-inch holes at 24 inches deep, which this calculator helps determine accurately.
Deck Posts: Contractors and homeowners planning deck projects use this tool to estimate concrete quantities needed for deck posts. Deck posts typically use 6×6 posts in larger holes (14-16 inches) at deeper depths (30-36 inches).
Mailbox Posts: Homeowners installing mailbox posts use this calculator to determine concrete quantities needed, ensuring sufficient materials are on-site before starting work.
Tips for Best Results
- Hole Size: Hole should be 2-3× post diameter (e.g., 4×4 post needs 10-12" hole)
- Hole Depth: Standard depth is 1/3 of post height above ground (e.g., 6 ft post = 24" deep hole)
- Add Waste: Always add 10% extra for waste, spillage, and mistakes during pouring
- Concrete Mix: Use appropriate concrete mix (2,500-3,000 psi) for post holes
- Frost Line: In cold climates, hole depth should be below frost line (typically 30-48 inches)
Frequently Asked Questions
How much concrete do I need for a 4×4 fence post in a 12-inch hole 24 inches deep?
For a 4×4 fence post in a 12-inch hole at 24 inches deep, you'll need approximately 1.57 cubic feet of concrete per post, or about 0.058 cubic yards. For 10 posts, you'll need about 15.7 cubic feet (0.58 cubic yards) or 27 bags of 80-pound concrete. Add 10% extra for waste.
How deep should a post hole be?
Standard post hole depth is 1/3 of the post height above ground. For a 6-foot post, use a 24-inch deep hole. For an 8-foot post, use a 30-36 inch deep hole. In cold climates, hole should be below frost line (typically 30-48 inches deep). Always check local building codes.
What size hole do I need for a 4×4 post?
For a 4×4 post, use a 10-12 inch diameter hole (2-3× the post size). Standard is 12 inches. Smaller holes (10") use less concrete; larger holes (14") provide more stability. The hole should be large enough to allow concrete to flow around the post.
How many bags of concrete do I need per post?
For a standard 4×4 post in a 12-inch hole at 24 inches deep, you'll need approximately 3 bags of 80-pound concrete or 4 bags of 60-pound concrete per post. Actual amounts vary by hole size and depth—use the calculator for accurate amounts.
Do I need to add extra concrete for waste?
Yes! Always add 10% extra for waste, spillage, and mistakes during pouring. If you need 15 cubic feet, order about 16.5 cubic feet (with 10% waste) to ensure you have enough concrete.
Can I use ready-mix concrete for post holes?
Yes, but ready-mix concrete is typically sold in cubic yards (minimum 1-2 yards), so it's more economical for multiple posts. For single posts or small projects, bagged concrete is more convenient. For large projects (10+ posts), ready-mix is usually cheaper.