How many bags of concrete for a mailbox post?
Quick Answer
One 50-lb bag of fast-setting concrete is typically enough for a mailbox post set in a 6–8 inch diameter hole 24 inches deep. If you're using a 4×4 wood post with a wider or deeper hole, use 1–2 bags of 80-lb mix. Mailbox posts don't need large footings — USPS guidelines require the post to break away easily in a collision.
Quick Reference Table
| Hole size | Concrete bags for mailbox post |
|---|---|
| 6" dia × 18" deep | 0.5 bag (50-lb) |
| 6" dia × 24" deep | 1 bag (50-lb) |
| 8" dia × 24" deep | 1 bag (80-lb) |
| 8" dia × 30" deep | 1–2 bags (80-lb) |
How to Calculate It Yourself
- 1
Dig a hole 6" in diameter and 24" deep with a post hole digger or auger.
- 2
Place the post in the center; check for plumb with a level.
- 3
Pour 1 bag of Quikrete Fast-Setting concrete dry into the hole.
- 4
Add water (about 1 gallon) per the bag instructions — no mixing required.
- 5
Hold plumb for 4 minutes; support with stakes for 4 hours before mounting the mailbox.
Pro Tip
Use fast-setting concrete (Quikrete 5000 or Fast-Setting) — you pour it dry into the hole, add water on top, and it sets hard enough in 4 hours. No mixing, no tools.
Assumptions to Check
Before ordering materials, confirm the dimensions, product coverage, waste factor, and local installation requirements for your project. Manufacturer coverage tables and local code rules can change the final quantity, especially for structural work, exterior projects, and irregular layouts.
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