# How Much Concrete Do I Need for a Fence Post? Hole size, concrete volume, and bags per post from the manufacturers' instructions, with a bags-per-hole table for 4×4 and 6×6 posts. Guide page: (published 2026-10-06, updated 2026-10-06). This Markdown version has the guide's key points, outline, FAQs and sources; the full article, with its worked examples and diagrams, is on the page. ## Key takeaways - QUIKRETE and Sakrete both size the hole from the post: about 3 times the post's width across, and 1/3 of the post's overall length deep, so 3 ft of a 9 ft post goes in the ground. - QUIKRETE's how-to page sets a shallower minimum, 1/3 to 1/2 of the height above ground: at least 2 ft for a 6 ft fence. - Concrete per hole = (hole area − post area) × the depth of concrete; divide by the bag's yield and round up. - A 4×4 in a 12 in hole with 27 in of concrete takes 1.58 cu ft: 4.20 bags of 50 lb fast-setting mix at 0.375 cu ft (buy 5) or 2.63 bags of 80 lb mix at 0.60 cu ft (buy 3). - For several posts, multiply the exact requirement by the number of posts and round up once. ## In this guide 1. [How big to dig the hole](https://www.howmanyyardsdoineed.com/guides/how-much-concrete-for-fence-posts/#hole-size) 2. [How much concrete fills a hole](https://www.howmanyyardsdoineed.com/guides/how-much-concrete-for-fence-posts/#concrete-per-hole) 3. [Bags per hole for 4×4 and 6×6 posts](https://www.howmanyyardsdoineed.com/guides/how-much-concrete-for-fence-posts/#bags-per-hole) 4. [How the setting method changes the count](https://www.howmanyyardsdoineed.com/guides/how-much-concrete-for-fence-posts/#setting-methods) 5. [Worked example: ten posts for a 6 ft fence](https://www.howmanyyardsdoineed.com/guides/how-much-concrete-for-fence-posts/#worked-example) 6. [Checking the arithmetic against the bag charts](https://www.howmanyyardsdoineed.com/guides/how-much-concrete-for-fence-posts/#bag-charts) 7. [Filling the hole and loading the post](https://www.howmanyyardsdoineed.com/guides/how-much-concrete-for-fence-posts/#filling-and-curing) 8. [Before you buy](https://www.howmanyyardsdoineed.com/guides/how-much-concrete-for-fence-posts/#before-you-buy) ## Frequently asked questions ### How many bags of concrete do I need per fence post? For a 4×4 in a 12 in hole with 27 in of concrete (a 36 in hole with 6 in of gravel under the post and the top 3 in left for soil), the concrete is 1.58 cu ft: 4.20 bags of 50 lb fast-setting mix at 0.375 cu ft each, or 2.63 bags of 80 lb concrete mix at 0.60 cu ft. Buy 5 or 3 for one post; for several posts, multiply before you round up. ### How big a hole do I need for a 4x4 fence post? QUIKRETE's how-to page says about 12 in wide for a 4 in wood post, three times the post's width, and Sakrete's data sheets also call for three times the post width. For depth, both makers' data sheets say 1/3 of the post's overall length, which is 3 ft for a 9 ft post. ### How deep should fence posts be for a 6 ft fence? QUIKRETE's how-to page says 1/3 to 1/2 of the height above ground, so at least 2 ft. QUIKRETE's data sheets and online calculator put 1/3 of the whole post in the ground: a 9 ft post with 3 ft buried. Local codes and frost depth can require more, so check before you dig. ### Do you have to mix fast-setting concrete for fence posts? Not with QUIKRETE's or Sakrete's post methods. QUIKRETE says to pour the dry mix to 3 to 4 in below the top of the hole and then add about 1 gallon of water per 50 lb bag. Sakrete says to fill the hole a third full of water first, then add the mix straight from the bag. Regular concrete mix is mixed before it goes in. ### How long before I can attach fence rails to new posts? QUIKRETE says its Fast-Setting Concrete Mix sets in 20 to 40 minutes and to wait 4 hours before putting any strain on the post. For QUIKRETE Concrete Mix the wait is 24 hours, and Sakrete says to wait at least 24 hours with its High-Strength mix. ### Should I put gravel in the bottom of a fence post hole? QUIKRETE's how-to page adds about 6 in of All-Purpose Gravel, compacted, and Sakrete's Fast Setting sheet calls for a 4 to 6 in compacted gravel base. QUIKRETE's Concrete Mix sheet puts 6 in of dry concrete mix in the bottom instead. Gravel takes the place of concrete; a dry-mix base is concrete, so it adds to the bag count. ## Related calculators and guides ### Calculators - [Concrete Calculator](https://www.howmanyyardsdoineed.com/concrete-calculator/) — Slab volume in cubic feet, cubic yards, and cubic meters, with ready-mix order size and bag counts for documented products. ### Guides - [Concrete Bag Yields by Bag Size](https://www.howmanyyardsdoineed.com/guides/concrete-bag-yields/) — Published cubic-foot yields for bagged concrete mixes, with bags per cubic foot, cubic yard, and cubic meter. - [How to Pour a Concrete Slab](https://www.howmanyyardsdoineed.com/guides/how-to-pour-a-concrete-slab/) — Plan, form, mix, place, finish, joint, and cure a slab, following the manufacturer's published method. - [Nominal vs. Actual Lumber Sizes](https://www.howmanyyardsdoineed.com/guides/nominal-vs-actual-lumber-sizes/) — A chart of real lumber dimensions from the national standard, dry versus green sizes, lengths, and board feet. ### Buying guides - [Best Concrete Mixers for DIY Slabs and Posts (2026)](https://www.howmanyyardsdoineed.com/best/concrete-mixers/) — Six drum and paddle mixers ranked on published specs for bagged concrete, with bags per batch and batches per slab or post worked out from the calculators. - [DEWALT vs Milwaukee Drill/Driver Kits Compared (2026)](https://www.howmanyyardsdoineed.com/best/dewalt-vs-milwaukee-drill-driver-kits/) — Seven 20V MAX and M18 drill/driver kits side by side on their makers' published specs, ranked for deck, drywall and fence work, with screw counts per job. ## Sources - [QUIKRETE Fast-Setting Concrete Mix (No. 1004) product data sheet: setting posts](https://www.quikrete.com/pdfs/data_sheet-fast%20setting%20concrete%20mix%201004-50.pdf) — QUIKRETE Companies. Used for: Final set in 20–40 min; 50 lb = 0.375 cu ft, 60 lb = 0.45 cu ft; hole about 3 × the post, 1/3 of the overall post height deep; dry mix to 3–4 in from the top, about 1 gal of water per 50 lb bag; holes deeper than 30 in filled in stages; wait 4 h before strain; two 50 lb bags set a 3 in square post in a 9 in × 30 in hole. Checked 2026-10-06. - [QUIKRETE Concrete Mix (No. 1101) product data sheet: setting fence posts](https://www.quikrete.com/pdfs/data_sheet-concrete%20mix%201101.pdf) — QUIKRETE Companies. Used for: Hole about 3 × the post, 1/3 of the overall post height deep; 6 in of dry concrete mix in the bottom; mixed concrete; wait 24 h before strain. Checked 2026-10-06. - [QUIKRETE Concrete Mix (No. 1101) product data sheet](https://www.quikrete.com/pdfs/data_sheet-concrete%20mix%201101.pdf) — QUIKRETE Companies. Used for: 40 lb = 0.30 ft³; 60 lb = 0.45 ft³; 80 lb = 0.60 ft³; 90 lb = 0.675 ft³ (regional). Checked 2026-10-03. - [Setting Posts without Mixing: QUIKRETE how-to video and project instructions](https://www.quikrete.com/athome/video-setting-posts.asp) — QUIKRETE Companies. Used for: Hole 3 × the post width (about 12 in for a 4 in wood post), 1/3–1/2 of the height above ground deep (at least 2 ft for a 6 ft fence); about 6 in of gravel; fill to 3–4 in below ground; about 1 gal of water per 50 lb bag; wait about 4 h. Checked 2026-10-06. - [QUIKRETE concrete calculator: Fast-Setting Concrete Mix for posts](https://www.quikrete.com/calculator/main.asp) — QUIKRETE Companies. Used for: Hole 1/2 of the above-ground post height deep (a 9 ft post: 6 ft above ground, 3 ft in the ground); post/hole pairs 2/6, 3/9, 4/12 and 6/18 in. Checked 2026-10-06. - [Sakrete Fast Setting Concrete Mix technical data sheet](https://www.sakrete.com/wp-content/uploads/2021/07/Fast-Setting-Concrete.pdf) — Sakrete. Used for: 50 lb = 0.38 cu ft; sets in about 1/2 hour; hole 1/3 of the post length deep and 3 × the post wide; 4–6 in gravel base; for an average 10 in hole: 1.25 bags at 12 in deep, 2 at 18 in, 2.5 at 24 in, 3 at 30 in. Checked 2026-10-06. - [Sakrete High-Strength Concrete Mix technical data sheet: posts and poles](https://www.sakrete.com/wp-content/uploads/2024/01/Sakrete-High-Strength-Concrete-Mix-TDS.pdf) — Sakrete. Used for: Depth 1/3 of the post length and diameter 3 × the post (a rule of thumb); mixed concrete rodded in and overfilled to slope; wait at least 24 h. Checked 2026-10-06. - [Voluntary Product Standard PS 20-25, American Softwood Lumber Standard: nominal and dressed sizes](https://www.nist.gov/system/files/documents/2024/12/11/PS%2020-25%20Final.pdf) — National Institute of Standards and Technology. Used for: Dry dressed: 1 → 3/4 in; 2 → 1-1/2; 4 → 3-1/2; 6 → 5-1/2; 8 → 7-1/4; 10 → 9-1/4; 12 → 11-1/4. Green: 2 → 1-9/16; 4 → 3-9/16; 6 → 5-5/8; 8 → 7-1/2. Timbers 5–6 in: 1/2 in off. Dry ≤ 19% moisture. Lengths in 1 or 2 ft multiples, trimmed 0 to 3 in over nominal. Checked 2026-10-05. **Estimate only.** Results are planning estimates computed from the numbers you enter. They are not engineering, structural, or code advice. Confirm quantities, product yields, and installation requirements with your supplier, the product label, and your local building authority before you order or build.