RightQty

Hardscape & masonry

Post hole concrete calculator

Calculate concrete volume and whole dry-mix bags for round post holes after subtracting the embedded post volume.

Post footings

Calculate concrete bags for post holes

Measurement system
Nominal dry-mix yield; verify the bag label.
Overage

Covers spillage, uneven depth, settling, and minor measurement differences.

Optional material costAdd your supplier's price

Material only; taxes, delivery, tools, reinforcement, and labor are excluded.

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Your material estimate

Concrete mix to buy

16bags

Includes 10% overage and purchase-unit rounding where applicable.

Post holes
4 holes
Concrete volume with overage
9.24 ft³
Selected bag yield
0.6 ft³/bag

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Shopping list

  • Concrete mix — 80 lb bagUses the selected nominal yield and includes 10% overage.16 bags
Calculation assumptions
  • Each hole is a uniform cylinder and every post extends through the entered hole depth.
  • The rectangular post displacement is subtracted from the cylindrical hole volume.
  • Bag count uses the selected 80 lb bag nominal yield; water content, waste, and actual bag yield can vary.
  • Footing diameter, depth, frost protection, uplift resistance, and structural suitability must be confirmed locally.

Volume-to-bag math

How post-hole concrete is calculated

1

Round hole volume

π × radius² × depth for each cylindrical hole.

2

Subtract the post

Remove rectangular post cross-section × embedded depth.

3

Convert to bags

Multiply by hole count, add overage, divide by nominal bag yield, and round up.

Site requirements

Verify diameter and depth before digging

Post size alone does not determine footing dimensions. Frost depth, soil, wind, uplift, structure loads, drainage, and local code can change the required hole.

Nominal bag yield

Dry-mix yields vary by product and mixing practice. Use the yield printed on the selected product when ordering.