Fence Post Concrete Calculator
Calculate how many bags of concrete you need for fence posts. Includes recommendations for hole size, depth, and fast-setting vs regular concrete.
How to Use This Calculator
Calculate concrete for fence post installation:
- Enter the total number of fence posts needed
- Select your post size (4x4, 6x6, or round)
- Choose hole depth based on fence height and frost line
- Select hole diameter (3x post width is recommended)
- Review concrete bag options including fast-setting formulas
Why This Matters
Properly set fence posts are the foundation of a durable fence. Undersized holes or insufficient concrete lead to leaning posts, especially under wind load or when gates are used heavily. Using the right hole depth prevents frost heaving in cold climates.
- Calculate exact concrete quantities for all posts
- Compare bag sizes (50lb, 60lb, 80lb options)
- Prevent mid-project supply runs
- Ensure posts resist lateral forces and wind loads
Worked Examples
Privacy Fence - 20 Posts
4x4 posts, 10 inch holes, 24 inches deep
Calculation: Hole: 0.436 cu ft - Post: 0.170 cu ft = 0.266 cu ft per hole × 20
Result: 10 bags (80lb) or 13 bags (60lb)
Heavy Gate Section
2 posts, 6x6 posts, 12 inch holes, 36 inches deep
Calculation: Each hole: 0.785 - 0.573 = 0.212 cu ft × 2
Result: 2 bags (50lb fast-setting)
Common Mistakes to Avoid
- Digging holes too shallow for fence height (leads to leaning)
- Not accounting for frost depth in cold climates (causes heaving)
- Making holes too narrow (not enough concrete grip)
- Overfilling holes with concrete (prevents drainage)
- Setting posts before checking string line alignment