Gravel Calculators
Fence Post Gravel Calculator
Fence posts don't need yards of stone — they need a drainage layer in the bottom of each hole. Enter your post count, hole diameter, and the gravel layer depth; results come in bags first, because that's how this job actually gets bought.
A note on this estimate
Hole walls collapse and tamping changes real usage, so treat the per-post figure as a planning number. The gravel here is a drainage layer only — the rest of the hole is concrete or tamped soil.
Last updated: 7 November 2026 · Report an error
How the per-post math works
Each gravel layer is a small cylinder: π × (hole radius)² × layer depth. A 12-inch hole with a 6-inch layer holds π × 6² × 6 ≈ 679 in³ ≈ 0.39 ft³ — not quite one 0.5 ft³ bag per post. Multiply by your post count for the total; a 24-post fence needs about 9.4 ft³ ≈ 19 bags (buy 20).
This is the smallest job on the site — which is why it's computed in cubic feet and bags, not yards and tons. If your number comes out in yards, you're filling entire holes with gravel, which is a different (and fine) approach: use the general gravel calculator on our homepage for that.
Hole sizes by post and fence height
Two rules of thumb size the hole. Diameter: about three times the post's width, so there is room to tamp the gravel or concrete around it in lifts. Depth: bury roughly a third to a half of the post's above-ground height — and in cold regions the hole must reach below the frost line regardless of what the ratio says, or frost heave will walk the post out of the ground.
| Post | Hole diameter | Fence height above ground | Hole depth |
|---|---|---|---|
| 4 × 4 in (3.5 in actual) | 10–12 in | 4 ft | 24–30 in |
| 4 × 4 in (3.5 in actual) | 10–12 in | 6 ft | 30–36 in |
| 6 × 6 in (5.5 in actual) | 14–16 in | 6 ft | 32–38 in |
| 6 × 6 in gate post | 16 in | 6 ft | 36–42 in — gates lever their posts hardest |
Worked example: 10 posts in 12-inch diameter, 36-inch deep holes. Each hole is π × 6² × 36 = 2.36 ft³ — about 4.7 standard bags, 247 lb of gravel. The run of ten totals 23.56 ft³ = 0.87 yd³ ≈ 1.24 tons, or 47 bags, which is why even a modest fence line usually justifies a bulk bag or a small delivery rather than retail bags.
Material choice: angular crushed stone, tamped in lifts — it locks around the post. Round pea gravel is the common mistake: it never locks, and the post works loose in its socket within a season or two. Keep the top of the fill a few inches below grade and crown soil or turf over it so surface water sheds away from the post instead of ponding in the hole.
Fence post FAQ
How much gravel do I need per fence post?
A typical 12-inch-wide, 6-inch-deep gravel base in the bottom of a post hole takes about 0.39 cubic feet — not quite one 0.5 ft³ bag. Most of the hole is filled with concrete or tamped soil; the gravel layer at the bottom is for drainage under the post.
Why put gravel in a fence post hole?
A layer of gravel under the post lets water drain away from the wood end grain instead of pooling and rotting it. Six inches of tamped gravel under the post is the standard detail for wood fence posts.
How deep should fence post holes be?
One-third of the above-ground fence height as a rule of thumb — a 6-foot fence wants 2-foot-deep holes, deeper in frost country so posts sit below the frost line. Hole diameter is typically 3 times the post width (10–12 inches for a 4×4 post).