Fence Post Concrete Calculator
Determine the exact number of concrete bags needed per post hole and total bags for your entire fence run.
- 30 × 80 lb bags of concrete mix (3 bags per post)
- 10 × fence posts
- 0.58 cubic yards total concrete volume (15.70 cu ft)
Standard Project Worked Example (No JavaScript Required)
Baseline Scenario: 10 posts, 4×4 post in 12 in diameter × 24 in deep hole (0% waste): 1.57 ft³/hole, 3 × 80 lb bags/hole, 4 × 60 lb bags/hole. Total for 10 posts: 30 × 80 lb bags.
Our online calculator updates dynamically in real-time as you type your project measurements. If JavaScript is disabled, use the formula reference below.
How This is Calculated
Hole volume is calculated using the cylinder volume formula V = π × r² × h minus the submerged post volume. Bags per hole = Volume / Bag Yield, rounded up. Total bags = Bags per hole × Post count.
Sourced Reference Constants
- All material yields and bag volumes are derived from official manufacturer technical data sheets.
- Buy quantities are strictly rounded UP to full purchasable units (bags, boxes, sheets, gallons, pavers).
- Waste allowances are user-adjustable to fit complex room alcoves, diagonal patterns, or soil conditions.
Frequently Asked Questions
How many bags of concrete per fence post?
A standard 4x4 post set in a 12-inch diameter hole 24 inches deep requires 3 bags of 80 lb mix (or 4 bags of 60 lb mix).
How deep should a fence post hole be?
Fence post holes should be dug to a depth equal to 1/3 to 1/2 of the above-ground post height, or below the local frost line in cold climates.
Do I need to mix concrete before pouring it in a fence post hole?
Fast-setting concrete can be poured dry directly into the hole and topped with water per manufacturer instructions (typically 1 gallon per 50 lb bag).