How Deep Should a Flagpole Foundation Be? Complete Depth Guide
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Your flagpole is only as stable as its foundation. Too shallow and it wobbles; too deep and you're wasting concrete and effort. Here's exactly how deep to go.
General Rule of Thumb
The foundation depth should be approximately 10% of the pole's above-ground height, with a minimum of 24 inches for any pole.
| Pole Height | Min Depth | Recommended | Hole Diameter |
|---|---|---|---|
| 15-20 ft | 24 in | 30 in | 12 in |
| 20-25 ft | 30 in | 36 in | 14 in |
| 25-35 ft | 36 in | 42 in | 18 in |
| 35+ ft | 42 in | 48 in | 24 in |
Adjustments by Soil Type
- Sandy soil: Add 6 inches to recommended depth
- Clay soil: Add 6-12 inches and include drainage (see our clay soil guide)
- Rocky soil: Standard depth is fine; rock provides excellent stability
- Loam: Standard depth works well
Wind Exposure Factor
If your property is in an open area with sustained winds above 30 mph, add 20% to the recommended depth. Check our wind and sizing guide for regional wind data.
Browse our residential and commercial flagpoles — each product page includes specific foundation requirements.
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