Concrete for a 4x4 Post: Bags per Hole
A 4x4 post measures about 3.5 × 3.5 in (measure yours). Quikrete's guide says a hole 3 times the post width: 10.5 in. At 30 in deep, with 6 in of gravel and the top 3 in left for soil, each hole takes 0.90 cu ft: about 2.4 bags of 50 lb Quikrete Fast-Setting (1.5 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 | 0.65 | 1.7 | 18 | 11 |
| 30 in | 0.90 | 2.4 | 25 | 16 |
| 36 in | 1.16 | 3.1 | 31 | 20 |
| 42 in | 1.42 | 3.8 | 38 | 24 |
Your posts
Set up for: 4x4 posts · Different project?
FAQ
How many bags of concrete for a 4x4 post?
About 2.4 bags of 50 lb fast-setting mix per hole at 30 in deep in a 10.5 in hole with a 6 in gravel base. Ten posts: 25 bags.
How wide should the hole be for a 4x4 post?
Quikrete's guide: three times the width of the post, so about 10.5 in for a 3.5 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.