Concrete for a 6x6 Post: Bags per Hole
A 6x6 post measures about 5.5 × 5.5 in (measure yours). Quikrete's guide says a hole 3 times the post width: 16.5 in. At 30 in deep, with 6 in of gravel and the top 3 in left for soil, each hole takes 2.23 cu ft: about 5.9 bags of 50 lb Quikrete Fast-Setting (3.7 of 80 lb Concrete Mix). For a 6 ft fence the guide gives 30–42 in deep.
By hole depth
| Hole depth | Cu ft per hole | 50 lb fast-setting per hole | 10 posts, 50 lb bags | 10 posts, 80 lb Concrete Mix |
|---|---|---|---|---|
| 24 in | 1.59 | 4.2 | 43 | 27 |
| 30 in | 2.23 | 5.9 | 60 | 38 |
| 36 in | 2.87 | 7.6 | 77 | 48 |
| 42 in | 3.51 | 9.3 | 94 | 59 |
Your posts
Set up for: 6x6 posts · Different project?
FAQ
How many bags of concrete for a 6x6 post?
About 5.9 bags of 50 lb fast-setting mix per hole at 30 in deep in a 16.5 in hole with a 6 in gravel base. Ten posts: 60 bags.
How wide should the hole be for a 6x6 post?
Quikrete's guide: three times the width of the post, so about 16.5 in for a 5.5 in post. Local rules can differ; check your building department.
Sources
- Quikrete: QUIKRETE guide: Setting Posts in Concrete · fetched and reviewed 2026-11-10
- Quikrete: QUIKRETE Fast-Setting Concrete Mix (No. 1004-50) data sheet · fetched and reviewed 2026-11-10
- Quikrete: QUIKRETE Concrete Mix (No. 1101) data sheet · fetched and reviewed 2026-11-10
Volumes only. ConcreteMath calculates volumes, bag counts, weights and your own cost figures. It gives no structural or engineering advice and never sizes footings, piers, slabs or rebar: those come from your plans, an engineer or your local building department. Bag counts are estimates from each maker's published yield; actual use varies with hole shape, uneven ground, waste and mixing. Bulk weights are published ranges; your supplier's figure wins.