How deep should you go when you set a fence post in concrete? For the same 8 ft post, two QUIKRETE instruction sets give hole depths up to 13 in apart. The steps are the same either way. The depth rule, the bottom layer and the wait before loading are where the instructions split.
Dig a hole 3 times the post width, add 6 in of gravel, plumb and brace the post, fill with concrete to 3 to 4 in below ground, then backfill with soil. QUIKRETE’s own documents differ on depth, bottom layer and wait time, so follow the bag you buy.
Six Steps to Set a Fence Post in Concrete
Dig the hole, add gravel, plumb and brace the post, fill with concrete, add water if you poured dry, then backfill with soil. These steps follow QUIKRETE’s Fast-Setting instructions.
- Dig. Make the hole 3 times the width of the post. A 3.5 in square post needs a hole 10.5 in wide.
- Add gravel. Pour in 6 in of gravel or crushed stone. QUIKRETE’s web page says to compact and level it with a post or a 2×4.
- Set and brace. Stand the post in the hole, check it is plumb, and hold it with braces (details below).
- Fill. Add concrete until it sits about 3 to 4 in below ground level.
- Add water. Dry-poured mix needs water poured on top. The project sheet says about 1 gallon for each 50 lb bag, depending on soil conditions.
- Backfill. Fill the rest with soil. The web page says to do this after the concrete has set.
Concrete Mix 1101 changes the bottom layer and the mixing, as the next section shows. To size the hole and count bags, use the Post Hole Concrete Calculator. This guide covers the method.
Why Do QUIKRETE’s Own Documents Give Different Depths?
Two of the documents cover Fast-Setting and one covers Concrete Mix, and they measure from different points. The project sheet and the Concrete Mix sheet use the overall post length. The web page uses only the length above ground.
| Instruction set | Hole depth rule | Bottom layer | Water and mixing | Wait before load |
|---|---|---|---|---|
| Fast-Setting project sheet | 1/3 of overall post length, plus 6 in | 6 in of gravel or crushed stone | Pour dry to 3 to 4 in from the top, then add water | Sets in about 20 to 40 minutes; heavy objects after 4 hours |
| Fast-Setting web page | 1/3 to 1/2 of above-ground length, plus 6 in | 6 in of gravel or crushed stone, compacted and leveled | Fill to 3 to 4 in below ground; “recommended amount” of water, none given | Not stated |
| Concrete Mix 1101 data sheet | About 1/3 of overall post height | 6 in of dry mix, not gravel | Mix with water before placing it in the hole | 24 hours before any strain |
Other brands will differ again. Read the sheet that came with your bag.
What Does an 8 ft Post Show About the Gap?
For one 8 ft post, the two Fast-Setting rules land 3 to 13 in apart. This is arithmetic on the manufacturer’s two formulas, not a recommendation.
- Project sheet: 96 in / 3 = 32 in, plus 6 in for gravel, gives a 38 in hole.
- Above-ground length: 96 – 38 = 58 in, assuming that 38 in hole.
- Web page: 58 / 3 = 19.33 in and 58 / 2 = 29 in. Add 6 in to get 25.3 to 35 in.
- Gap: 38 – 35 = 3 in and 38 – 25.3 = 12.7 in.
- Width: 3 x 3.5 in post = 10.5 in.
Follow the instructions on the bag you buy. For structural posts, local code comes first.
How Do You Plumb and Brace the Post?
Check the post for plumb on two sides, then hold it with braces while you fill. QUIKRETE’s web page describes a method that needs only a few parts.
- Fasten angled 2×4 braces to two adjacent sides of the post, one screw per brace.
- Drive a stake near the lower end of each brace.
- Check plumb on two sides, then fasten the braces to the stakes.
The project sheet adds one more check: after the dry mix goes in, recheck plumb and brace as needed.
Dry Pour or Wet Mix: How Does the Hole Fill?
Fast-Setting goes into the hole dry and is soaked with water there. Concrete Mix is mixed with water first. QUIKRETE’s product page says Fast-Setting sets posts without mixing.
That is the answer to setting a post without mixing. Pour the dry mix until it is 3 to 4 in from the top, recheck plumb, then pour water on and let it soak in. The product page says No. 1004 sets hard in about 20 to 40 minutes and comes in 50 lb bags.
Deeper holes get a staged fill. The 38 in example is deeper than 2-1/2 ft, so the project sheet’s step applies: fill with mix to 2-1/2 ft or less, add water, wait until it soaks in all the way, then add the rest of the mix and water. For loose or sandy soil, the sheet says to dig a larger, dish-shaped hole, and the web page recommends a tube form. Our Sonotube calculator sizes tube forms.
How Long Before You Can Load the Post?
With Fast-Setting, QUIKRETE says heavy objects such as basketball backboards can hang from the post after 4 hours. With Concrete Mix, its data sheet says to wait 24 hours before the post takes any strain.
Below 72 F, the project sheet says more curing time is needed. Setting in 20 to 40 minutes is not the same as being ready for a heavy load, and the sheet’s own heavy-object wait is 4 hours. The web page gives no wait time, and none of the documents names a gate, so check the bag you bought. For other quick-setting jobs, try our fast-setting concrete calculator.
Rot, Rust and When to Check Local Code
Use pressure-treated lumber for wood posts, coat metal posts with rust inhibitor, and check local code for any structural post. QUIKRETE’s project sheet gives the first two as tips.
- Wood: pressure-treated lumber, or a creosote equivalent, prevents below-ground rot.
- Metal: a rust inhibitor coat goes on before the post is set.
- Structural posts: for posts such as decking, the hole must reach at least 6 in below the frost line.
- Equipment poles: for basketball poles and similar gear, follow the equipment maker’s hole depth and size.
The Concrete Mix data sheet says that load-bearing uses must follow local building codes. When a post holds up a deck or a roof, stop and check code before you dig. Our foundations and footings calculators cover larger structural pours.
Enter your post size and hole depth to work out hole size and bags for your posts.
Keep reading: how deep footings should be, how much water goes in the mix and ready-mix versus bagged concrete.
More: all construction guides.
FAQs About Setting Fence Posts in Concrete
Can you set a fence post without mixing the concrete first?
Yes, with Fast-Setting Concrete. QUIKRETE says to pour the dry mix into the hole and soak it with water. Concrete Mix 1101 is different: its data sheet says to mix with water before placing it.
How long before I can hang a gate or backboard on the post?
QUIKRETE says heavy objects such as backboards can hang after 4 hours with Fast-Setting, and longer below 72 F. Its Concrete Mix sheet says 24 hours. The documents do not name gates.
Do I need braces when setting a post in concrete?
QUIKRETE’s web page describes angled 2×4 braces on two adjacent sides, fastened to stakes, with plumb checked on two sides. The project sheet says to recheck plumb after the dry mix goes in.
Can I use Concrete Mix instead of Fast-Setting for a post?
QUIKRETE gives post instructions for both. Concrete Mix 1101 uses 6 in of dry mix at the bottom instead of gravel, is mixed with water first, and needs 24 hours before strain.
What should I do in loose or sandy soil?
QUIKRETE’s project sheet says to dig larger, dish-shaped holes for posts in loose or sandy soil. Its web page recommends a tube form. A tube form can be placed in the hole and backfilled first.
How do I protect wood and metal posts below ground?
QUIKRETE’s tips say to use pressure-treated lumber, or a creosote equivalent, to prevent below-ground rot. For metal posts, coat them with a rust inhibitor.
What if the post hole is deeper than 2-1/2 feet?
QUIKRETE’s project sheet says to fill with mix to a depth of 2-1/2 ft or less, add water, and wait until it soaks in all the way. Then add the rest of the mix and water.
Sources and Further Reading
References Used in This Article
- QUIKRETE, Setting Posts project sheet (PDF), accessed 2026-10-19.
- QUIKRETE, Setting Posts web page, accessed 2026-10-19.
- QUIKRETE, Concrete Mix 1101 data sheet (revised October 2022), accessed 2026-10-19.
- QUIKRETE, Fast-Setting Concrete Mix product page, accessed 2026-10-19.
Instructions here follow the manufacturer’s documents named in Sources and apply to its products. Reviewed for accuracy by Prof. Dr. Khalil Mudassar, PhD. Last updated 2026-10-19.
Shakeel Muzaffar is the Founder and Editor-in-Chief, with over 15 years of experience in digital publishing and online tool development. He oversees editorial quality and formula verification to ensure accurate, practical, and easy-to-use calculators.