Concrete calculator · post holes v1.0
Post Hole Concrete Calculator
Calculate concrete for matching or mixed post holes. Enter the hole and post dimensions already specified for the project, then see net volume, allowance, whole bags, a ready-mix equivalent and optional cost separately.
✓No signup
✓Multiple hole groups
✓Post displacement
✓Verified bag yields
Step 1
Enter the measured hole groups
Keep matching holes together and add another group when corner, end, gate or other holes use different dimensions. How to measure a post hole for concrete.
Hole and post measurements
Use the concrete-filled depth, which can differ from the total excavated depth. Actual post dimensions are used only to subtract the space occupied within that concrete.
Quantity estimate only. This calculator does not choose the hole diameter, depth, spacing, post embedment, concrete strength or structural detail.
Ordering & pricing
Advanced assumptions
How the post-hole concrete calculation works
The calculator finds the gross volume of each hole, subtracts only the part of the post that lies within the concrete-filled depth, and multiplies the net volume by the number of identical holes. Every group is combined before the allowance and whole-bag rounding are applied.
Concrete per hole = hole cross-section × fill depth − post cross-section × post length within concrete
Adjusted project concrete = all group volumes × (1 + allowance ÷ 100)
Whole bags = adjusted volume ÷ published product yield, rounded up
Round and rectangular holes or posts
Hole shape and post shape are independent. The calculator supports round or rectangular holes, with no post, a round post or a rectangular post. It checks physical fit as well as volume, including the diagonal of a rectangular post inside a round hole.
Use actual finished post dimensions. A nominal product description may not equal its measured cross-section.
Concrete bags use product yield, not bag weight alone
The result uses the published cubic-foot yield of the selected concrete product. The same bag weight can represent different products, so the data sheet or current label for the exact mix takes priority. The list includes standard Concrete Mix yields from the QUIKRETE Concrete Mix Data Sheet 1101 plus verified QUIKRETE and Sakrete fast-setting product yields.
Safety and project scope
This calculator applies only where concrete or post-setting mix is already specified. It does not decide whether concrete, driven posts, ground screws, sleeves or surface-mounted bases are appropriate.
Before digging in the United States, use the applicable underground-service locating process; 811 Before You Dig explains the national 811 process. Follow the exact product label and safety data sheet: cement dust and wet concrete can injure skin and eyes. Hole sizing, embedment, frost, soil, wind, gate, deck and other loading decisions require project-specific information.
Post hole concrete calculator FAQs
Does the calculator subtract the post from the hole volume?
Yes. It subtracts the volume occupied by the post only within the concrete-filled depth before group quantity, allowance or purchase rounding is applied.
Can I calculate a square post inside a round hole?
Yes. Hole and post shapes are separate inputs. The calculator also checks that the rectangular post diagonal is smaller than the round hole diameter.
How many concrete bags do I need per post?
That depends on the measured hole, post displacement, allowance and exact product yield. The result shows net concrete per hole and rounds the combined project quantity to whole bags.
What if corner or gate-post holes are larger?
Add them as a separate hole group. Different dimensions should not be hidden inside one average hole size.
Will this calculator tell me how deep or wide to dig?
No. It estimates material from dimensions you supply; it does not design the hole or determine soil, frost, embedment, structural or code requirements.
Need another concrete quantity? Use the Concrete Footing Calculator for strip or pad foundations, or read the measurement guide before entering mixed post-hole groups.
Measure Post Holes for Concrete