How to set fence posts in concrete (and not have them lean)

Published April 9, 2026 by the FenceCalc team

Builder filling a post hole with concrete to anchor a freshly set fence post — Photo via Pexels

My first DIY fence leaned within one winter. Every single post tilted at least 2 degrees. A few tilted 10. I'd dug the holes too shallow, used half the concrete I should have, and the whole 120ft run looked like a drunk snake by January. Tore it out the next spring and started over.

That second fence has been standing straight for eight years. Same lumber. Same posts. Same soil. The difference was how I set the posts. Here's the real method, the one that works.

Hole depth, the single most important decision

One-third of the post's total length. Minimum. Or to the local frost line, whichever is deeper.

For a 6ft fence you're using 8ft posts (6ft above grade, 2ft buried). That's a 24-inch minimum hole. If you're in Minnesota, Michigan, or northern Colorado, your frost line is 42-48 inches and you need a deeper hole regardless. For a 4ft fence, an 18-inch hole on a 6ft post is the minimum. For 8ft fence, you're at 36 inches minimum on a 10ft post.

Shallow holes are the number one reason fences lean. Frost heave lifts shallow posts. Wind pressure on a 6ft privacy fence is substantial (a 6mph wind generates about 1 psf of lateral pressure, and a 150ft fence catches a lot of air). A shallow post with inadequate concrete is going to give up.

Hole diameter

Three times the post width. A 4x4 post needs a 12-inch diameter hole. A 6x6 needs 18 inches. Too narrow and the concrete doesn't have enough cross-section to resist lateral load. Too wide and you're wasting concrete.

A manual Wolverine post hole digger handles 12-inch holes fine. Anything bigger and you want a power auger. Home Depot, Lowe's, and Sunbelt Rentals all rent two-man gas augers for $80 to $110 a day. Worth it for anything over 20 posts.

Drainage, the detail nobody talks about

Put 2-4 inches of drainage gravel at the bottom of every hole before you set the post. Pea gravel or 3/4-inch crushed stone. About $4 per bag from Home Depot, and one bag covers 8-10 holes.

Why it matters: water runs down the post and into the concrete over the years. If there's no drainage, water pools at the base and rots the bottom of a wood post. A 2-inch gravel bed gives the water somewhere to go and buys you 5-10 extra years on wood posts. Skip this step and your treated pine post will rot out at the base in 7-9 years even with perfect concrete.

Quikrete vs Sakrete, the fast-set concrete question

Both work. Quikrete 50lb fast-setting is the most common. Sakrete 50lb fast-setting is functionally identical. Menards carries their own house brand that's also fine. Don't bother with regular Portland and mixed concrete for fence posts, fast-set is worth the small premium for the 40-minute cure time alone.

One 50lb bag per post for a 6ft fence is the minimum. Two bags per corner post, gate post, or terminal post. Gates especially. A flimsy gate post with one bag of concrete is going to sag within two years no matter how good your gate hardware is.

Don't mix the concrete. Modern fast-set is designed to be poured dry into the hole around the post, then hit with water from a garden hose. Mix it in the hole, in place. Less mess, less mixing time, sets up harder because the water-to-cement ratio is controlled by the natural draw of moisture.

The actual method, step by step

Dig the hole to depth. Check depth with a tape every hole. "Eyeballing it" is how 18 of your 20 holes end up two inches shallow.

Pour 2-4 inches of gravel at the bottom.

Set the post in the hole. Check plumb with a 4ft level on two adjacent faces. Use a temporary brace (a scrap 2x4 nailed loosely between two stakes) to hold it vertical while you pour.

Pour one full bag of dry Quikrete around the post. Fill to about 3 inches below grade.

Pour a gallon of water on top, slowly. Let it soak in. You'll see the concrete darken and start to set up within 60-90 seconds.

Recheck plumb. Adjust if needed, you have maybe 8-10 minutes before it's too late.

Move to the next post. Come back in 40 minutes and the concrete will be fully set. You can hang rails within an hour.

The crown

Once the concrete sets, add a small mound of dirt or concrete on top of the hole, slightly higher than grade, sloping away from the post. This is the crown. It sheds rainwater away from the post base instead of letting it pool.

If you don't crown, water pools and eventually finds its way down the wood-concrete interface, and you're back to rotting posts. Skipping the crown is the #2 reason after shallow holes that DIY fences fail early.

Deep hole, gravel bottom, plumb post, two bags of Quikrete on terminal posts, crown the top. Five details. Every one of them matters.

What about metal post anchors?

Simpson Strong-Tie makes a post-base anchor (the PBS series) that lets you set a concrete pier first, then bolt the post to the anchor above grade. Keeps the wood completely out of the concrete. Lasts significantly longer on wood posts.

Downside: more expensive, more time, and for a privacy fence the lateral load on the top of the post is substantial. Anchors are better for deck posts and pergolas than for fence posts. For fencing, traditional in-concrete setting is still the right call.

Common mistakes

Setting posts first, then coming back to do all the concrete at once. Fine for anchors but terrible for fence posts. By the time you pour the last bag, the first posts have shifted out of plumb.

Using regular Quikrete (not fast-set) and walking away for 24 hours. Wood shrinks and swells overnight. Your cured posts will be slightly out of plumb by morning, and now you can't fix them.

Mixing the concrete in a wheelbarrow and troweling it into the hole. Extra work, more mess, and the water ratio is almost always wrong (too wet, too slow-setting, weaker final strength). Use the dry-pour method.

Setting posts during rain. Water dilutes the concrete, changes the ratio, and weakens the set. Pick a dry day. If a thunderstorm rolls in, cover the fresh holes with a tarp.

Use the calculator

If you're planning DIY, use the FenceCalc estimator with DIY selected to see materials cost. Plan on two bags of Quikrete per terminal post (corners and gates) and one bag per line post. A 150ft fence at 8ft post spacing needs about 20 posts, so budget 22-25 bags of Quikrete. That's about $140 at Home Depot.