Take out the space a round post fills.
⚙️Calculation Parameters
📊Calculated Output
How Round Post Displacement Calculator Works?
To subtract a round post, the Round Post Displacement Calculator removes the buried part of the post from the hole volume. The process takes 4 steps.
Enter the hole or tube
Type the hole or form diameter and its depth.
Enter the post
Type the post diameter and the embedded length.
Subtract the post
The calculator finds the post cylinder and subtracts it.
Read net concrete
The tool shows the concrete in cubic feet (ft³), liters (L) and bags.
Round Post Displacement Calculator Formula
The Round Post Displacement Calculator subtracts one cylinder from another.
Hole
V_h = π × (D_h ÷ 24)² × (H ÷ 12)Full hole volume.
Post
V_p = π × (D_p ÷ 24)² × (E ÷ 12)E is embedded post length.
Net concrete
V = V_h − V_pConcrete around the post.
Worked example: 12 in hole, 36 in deep, 6 in round post
- V_h = 2.356 ft³
- V_p = 0.589 ft³ (25% of the hole)
- V = 1.767 ft³ → 3 bags of 80 lb instead of 4
Round Post Displacement Calculator Conversion Table
The round post displacement conversion table lists 6 hole and post pairs at 36 in (91 cm) deep.
| Hole | Post dia. | Hole ft³ | Post ft³ | Net ft³ | 50 lb bags |
|---|---|---|---|---|---|
| 8 in | 4 in | 1.047 | 0.262 | 0.785 | 3 |
| 10 in | 4 in | 1.636 | 0.262 | 1.374 | 4 |
| 10 in | 5 in | 1.636 | 0.409 | 1.227 | 4 |
| 12 in | 6 in | 2.356 | 0.589 | 1.767 | 5 |
| 12 in | 8 in | 2.356 | 1.047 | 1.309 | 4 |
| 16 in | 10 in | 4.189 | 1.636 | 2.553 | 7 |
Set 4 in to 6 in of gravel under the post end, if the design calls for drainage.
What is Round Post Displacement Calculator?
A Round Post Displacement Calculator is a calculator that subtracts an embedded round wood or steel post from the concrete needed for its hole.
A post takes up space in the hole. A 6 in pole in a 12 in hole fills 25% of the volume, so ordering for an empty hole buys 25% too much. The calculator removes that space and gives the true fill.
Round posts include utility poles, landscape timbers, steel pipe posts and peeled log posts.
What are the uses of Round Post Displacement Calculator?
There are 4 main uses of the Round Post Displacement Calculator.
Pole barns
Builders set round poles in concrete collars.
Steel pipe posts
Installers set pipe fence and gate posts.
Clotheslines and swings
Owners set round steel posts in the yard.
Log structures
Crews set round timber posts.
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