Post Hole Concrete Calculator

Calculate exactly how much concrete you need to set fence posts, deck posts, or mailbox posts — including bag counts, cost, gravel base, and a 10% waste buffer.

Units:
Post shape
Post dimensions
E.g. 3.5 for a nominal 4" round post Enter a valid positive value
Total height of post above ground Enter a valid positive value
Hole dimensions  Auto-filled from post size — adjust if needed
Rule: 3× post width Enter a valid positive value
Rule: ⅓ of post height Enter a valid positive value
Total holes to fill Enter at least 1
Optional — gravel base & cost
For drainage (optional)
Local store price (optional)
Used for cost row
1
Select post shape — choose Round for circular posts or Square for timber 4×4 / 6×6 posts.
2
Enter post size and height — type the post's diameter or width and the post height above ground. The hole dimensions auto-fill using standard rules.
3
Adjust hole dimensions if needed — auto-fill follows the rule of thumb (hole = 3× post width, depth = ⅓ post height). Override for your project or local frost-line requirements.
4
Add gravel base & price (optional) — open the optional section to add a gravel drainage layer and your local bag price for an instant cost estimate.
5
Read results & download — see total concrete, bag counts, cost, gravel, and a 10% waste buffer. Download the branded PDF report for your records.
Pro tip: Always buy the "with 10% waste" amount — concrete can't be returned once mixed, and running short means a second trip mid-job. In cold climates, check your local frost line depth; post holes must extend below it.

How Concrete-Depot's tool compares to the most popular post hole calculators online:

Calculator Round + Square Auto hole size Post subtraction Bag counts Cost estimate Gravel base 10% waste PDF report Metric
★ Concrete-Depot.com ✔✔✔ ✔✔✔ ✔✔✔
Inch Calculator ✖✖✖ ✔✔✖ ✖✖✔
Omni Calculator ✔~✔ ✖✖✖ ✖✖✔
Builder's Calculator ✔✔✖ ✖✖✔ ✖✖✖
SkilledHub ✖✖~ ✖✖✖ ✖✖~
concrete-calculator.org ✖✖✖ ✖✖✖ ✖✖✖

~ = partial support | Last reviewed May 2026