A fence is only as straight and solid as its posts. Set them well and the rest of the build is easy; rush them and the whole line leans within a season. Setting a post isn’t hard, but the details — depth, a gravel base, staying plumb, and letting the concrete cure — are what separate a fence that lasts 20 years from one that wobbles. Here’s the step-by-step.
What you’ll need
- Post-hole digger or power auger
- Gravel (for drainage at the base)
- Fast-setting or standard concrete mix
- A level, and stakes plus scrap boards for bracing
- Tape measure, and a string line for aligning multiple posts
Step 1: Dig the hole to the right depth
Dig so that at least one-third of the post’s total length is below ground, or a minimum of 2 feet — whichever is deeper. In cold climates, go below the frost line even if that’s deeper still, or winter heave will lift the post. Make the hole about three times the post’s width (roughly 8–12 inches for a 4x4) and flare it slightly wider at the bottom to resist uplift.
Not sure how much concrete each hole takes? The Fence Post Concrete Calculator gives an exact 60 lb / 80 lb bag count from your hole size and post count.
Step 2: Add a gravel base
Pour 4–6 inches of gravel into the bottom of the hole and tamp it down. This lets water drain away from the base of the post instead of pooling against it — the single best thing you can do to prevent a wood post from rotting where it meets the concrete.
Step 3: Set the post and get it plumb
Place the post on the gravel and check it with a level on two adjacent sides so it’s plumb in both directions. Attach two braces (scrap boards screwed to the post and staked to the ground) to hold it exactly in position. If you’re setting a run of posts, pull a string line between your end posts and align each post to it before bracing.
Step 4: Pour the concrete
Add concrete mix around the post, following the bag’s instructions:
- Fast-setting mix: pour the dry mix into the hole, then add water on top (or per the bag). It sets in 20–40 minutes — great for a quick job.
- Standard mix: mix with water first, then shovel it in, working out air pockets with a stick.
Fill to just above ground level and slope the top away from the post so rainwater runs off instead of sitting against the wood.
Step 5: Re-check plumb, then let it cure
Before the concrete hardens, check plumb one more time and adjust while you still can. Then leave it alone. Even fast-setting concrete needs a few hours before it takes load, and reaches full strength over a few days. Don’t hang gates or stretch fence between posts until the concrete has cured — this is the step people skip, and it’s why posts end up crooked.
Common mistakes to avoid
- Too shallow. The number one cause of leaning fences. When in doubt, dig deeper.
- No gravel. Water pools at the base and rots the post from the bottom up.
- Concrete below grade. If the top of the concrete sits in a dish below ground, it collects water. Crown it above grade.
- Rushing the cure. Bracing and patience are free; re-setting a leaning post is not.
Plan the whole job first
Setting posts is one step of the build. Before you dig, work out how many posts you need and how far apart with the Fence Material Calculator, then get the exact concrete for those holes with the Fence Post Concrete Calculator. A few minutes of planning saves a second trip to the store — or a second attempt at a crooked post.
General guidance only — always follow your concrete product’s instructions and local building code for depth and footing.