Post Hole Concrete Calculator
Enter your hole diameter, depth and number of posts to get the total bags of concrete to set them.
- Concrete per hole
- 0.7 ft³
- Total concrete
- 6.98 ft³
A hole 3× the post width and about 1/3 the post height deep is standard. Use fast-setting mix for posts.
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How to calculate it
Enter your hole diameter, depth and number of posts to get the total bags of concrete to set them.
Source: Hole volume = cylinder area × depth; 80-lb bag yields ≈ 0.60 ft³, 60-lb ≈ 0.45 ft³, 50-lb ≈ 0.375 ft³.
Ten 4×4 posts in 8 in wide × 24 in deep holes: each hole = π × 4² × 24 ÷ 1728 = 0.698 ft³. Ten holes = 6.98 ft³ ÷ 0.60 = 12 → 13 bags with waste.
Want the full step-by-step walkthrough? Read our How to Plan a Wood Fence: Posts, Pickets & Concrete.
Purchasing & waste guidance
- A hole 3× the post width and 1/3 the post height in the ground is standard.
- One 80-lb bag per post covers an 8 in × 24 in hole for a 4×4; add a bag for 6 ft fences or loose soil.
- Use fast-setting mix for posts — you can often set the post and backfill in one step.
- Call 811 before digging to mark underground utilities.
Assumptions & what’s included
- Holes are cylindrical with the entered diameter and depth.
- Bag yields use manufacturer averages (50 lb ≈ 0.375, 60 lb ≈ 0.45, 80 lb ≈ 0.60 ft³).
- Waste allowance covers spillage and uneven holes. Price is per bag and optional.
Frequently asked questions
How many bags of concrete do I need per fence post?
A 4×4 post in an 8 in wide × 24 in deep hole needs about 0.7 ft³, or two 80-lb bags per post. Use three bags for 6 ft fences or loose, sandy soil.
How deep should a post hole be?
Dig the hole about 1/3 the post height plus 6 in of gravel for drainage. A 6 ft fence post typically needs a 24 in deep hole. Make the hole 3× the post width.
How wide should a post hole be?
About 3× the post width — an 8 in hole for a 4×4 post. Wider holes give more concrete and a stronger setting, especially in loose soil.
Related guides
Step-by-step project guides that use this calculator.