Six 12"×36" holes
- Total volume ≈ 14.1 cu ft
- ≈ 0.52 cu yd
construction calculator
Post Hole Concrete Calculator
Estimate concrete volume for fence or deck post holes by entering hole size and count.
Results
- Cubic feet
- 14.14
- Cubic yards
- 0.52
How to use this calculator
- Enter how many holes you’re digging plus their diameter and depth in inches.
- We calculate the cylindrical volume per hole and multiply by the hole count.
- See cubic feet and cubic yards to size bag orders or ready-mix deliveries.
Inputs explained
- Number of holes
- Total fence, deck, or sign posts you’re setting.
- Hole diameter
- Width of the hole in inches. Use the widest point if holes are irregular.
- Hole depth
- Depth in inches down to the bottom of the hole.
How it works
We treat each hole as a cylinder: volume = π × radius² × depth. Multiply by the number of holes to get total volume.
Outputs show both cubic feet and cubic yards so you can convert to bag counts or truck orders.
Formula
Volume per hole = π × (diameter/2)^2 × depth
When to use it
- Sizing concrete for fence posts, pergola footings, or mailbox posts.
- Estimating how many bags to load before heading to the store.
- Checking if a small mixer can handle the volume versus ordering a short-load truck.
Tips & cautions
- Add 5–10% extra to cover overdigging, soil collapse, or spillage.
- Verify local frost depth and code requirements for post embedment.
- Use sonotube diameters when possible—they’re easier to measure consistently.
- Assumes straight cylindrical holes; flared bases aren’t modeled explicitly.
- Does not subtract volume for posts themselves—add a small cushion if posts displace concrete.
- No automatic bag conversion here—combine with the concrete bag calculator if needed.
Worked examples
Ten 9"×30" holes
- Volume ≈ 13.8 cu ft
- ≈ 0.51 cu yd
Deep dive
Estimate concrete for post holes by entering hole count, diameter, and depth to get cubic feet and yards.
Great for fence and deck projects when you need a quick volume check before buying bags or ordering a truck.
FAQs
- How much extra should I order?
- Add 5–10% to account for soil collapse, overdigging, and spillage.
- Does it handle belled holes?
- This version assumes straight cylinders. Use the largest diameter for belled bottoms.
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Measurements are estimates. Verify onsite dimensions before ordering materials.