Post-Hole Concrete Calculator
Bags of concrete to set fence or deck posts.
Make it a complete project
Check the steps, tools, and DIY difficulty before you shop. Your calculator results can be added to My Projects above.
Find help for this project
Check for a contractor serving your project location. Your calculator stays free wherever you live.
Optional. Your ZIP stays in this tab and is not sent to analytics. Availability is based on approximate ZIP locations; confirm your address with the contractor.
For contractors: take the next step with Job Ready IQ.
Explore estimating tools for your business from the team behind Honey-Do Squad.
Explore Job Ready IQ →
Setting posts in concrete is the foundation of fences, mailboxes, decks, and pergolas. The trick is the right hole size, depth below the frost line, and keeping the post plumb while the concrete sets.
DifficultyBeginner
TimeAn afternoon to dig and set a handful of posts, plus cure time
SkillsComfortable digging and checking plumb with a level
PermitsCall 811 before digging. Structures (decks, large pergolas) may need a permit and inspected footings.
Tools you'll need
- Post hole digger or auger
- Post level
- Bags of fast-setting concrete
- Wheelbarrow or mixing tub
- Tamper
- Scrap lumber for bracing
Step by step
- Call 811 and dig Locate utilities first — call 811 at least 2–3 business days ahead (free, and the law). Dig the hole about 1/3 of the post length and below your local frost line — typically 24–36" for a fence post.
- Add a gravel base Put a few inches of gravel in the bottom so water drains away from the post end and it doesn't rot.
- Set and brace the post Stand the post on the gravel, brace it plumb with scrap lumber, and check both directions with a level.
- Pour the concrete For fast-set mix you can pour the dry mix in and add water on top per the bag. Mound the top and slope it away from the post to shed water.
- Let it cure Leave the bracing on. Fast-set firms in ~30–60 minutes but reaches strength over a day or two — don't hang anything heavy until then.
Common mistakes
Holes too shallow
Bury ~1/3 of the post and go below frost line, or posts heave and lean.
No gravel under the post
A gravel base lets water drain and dramatically slows rot.
Concrete mounded toward the post
Slope the top away from the post so water sheds instead of pooling at the wood.
Safety
- Call 811 and wait for the locate before digging.
- Concrete mix is caustic — wear gloves and eye protection.
Frequently asked questions
How deep should a post hole be?
About a third of the post length and below the frost line — usually 24–36" for a 6 ft fence post.
How much concrete per post?
Commonly 1–2 bags of 60-lb fast-set. Enter your hole size and post count above for an exact bag count.
Do I need to mix fast-set concrete?
No — you can pour the dry mix into the hole and add water per the bag. It's the easiest way to set posts.
Next steps for this project
Fence
Posts, rails, pickets and concrete for a wood fence.
Deck Framing
Joists, beam, posts and hangers for a deck frame.
Concrete Slab
How much concrete you need for a slab, driveway, or patio — in cubic yards and bags.
Gravel
How much gravel you need for a driveway, path, or base — in tons and cubic yards.