Fence Post Depth Calculator
Fence posts fail when the holes are too shallow. Enter your fence height and local frost-line depth to get the right hole depth, the post length to buy, and a concrete estimate.
Rule of thumb: bury at least one-third of the post, or 24 inches minimum — and always dig below the frost line so freeze-thaw cycles do not heave the posts.
How the fence post depth calculator works
A fence post needs enough buried length to resist wind leverage and frost heave. This calculator takes the strictest of three rules: a 24-inch absolute minimum, 6 inches below your local frost line, and one-third of the above-ground height — then rounds up to the next whole inch.
It also tells you what length of post to buy (above-ground height plus buried depth, rounded up to standard 6, 8, 10, 12, 14, or 16 ft lengths) and estimates 80 lb concrete bags for a 10-inch-diameter hole, since most DIY posts are set in concrete.
hole depth = max(24″, frost + 6″, ⌈above-ground″ ÷ 3⌉) · bags = ⌈hole volume ÷ 0.6 ft³⌉
Related tools
Keep exploring: Concrete Slab Calculator · Gravel Calculator · Sand Calculator.
Fence post depth calculator FAQ
How deep should posts be for a 6 ft fence?
At least 24 inches — one-third of 72 inches is exactly 24. In cold climates, dig 6 inches below the frost line instead, which may be deeper.
Should I use concrete or gravel for fence posts?
Concrete locks posts firmly and is best for gates and corners that take loads. Compacted gravel drains better and suits line posts in wet ground, but allows slight movement.
What is the frost line and why does it matter?
The frost line is how deep the ground freezes in winter. Posts set above it get pushed upward by freeze-thaw cycles (frost heave). Digging 6 inches below it keeps posts stable.
Do corner and gate posts need deeper holes?
Yes — gates and corners carry extra load and wind force. Go 6 inches deeper than the calculator suggests and use a wider hole for those posts.
How many concrete bags per post?
For a 10-inch-diameter hole, each 80 lb bag fills about 0.6 cubic feet. A 24-inch-deep hole needs about 2 bags; the calculator above sizes it for your exact depth.