{ "slug": "concrete-fence-post-calculator", "title": "Concrete for Fence Posts Calculator", "heading": "Concrete for Fence Posts Calculator", "category": "other", "url": "https://www.revenuelab.fyi/toolbox/concrete-fence-post-calculator", "summary": "Bag count for setting a whole run of fence posts in concrete footings.", "description": "Setting fence posts in concrete means digging a round hole per post, dropping the post in, and filling the annular gap around it with concrete — and the volume needed per hole is the hole's cylindrical volume minus the volume the post itself displaces. This calculator takes your hole diameter and depth, your post's cross-section width (treated as displacing a square footprint, a reasonable approximation for both square and round posts), and your total post count, then computes cubic feet per hole, converts to 80lb bags using the standard 0.6 cubic feet per bag yield, and multiplies by the number of posts for a total order. Fence contractors typically use one to two 50lb 'fence post mix' quick-set bags per post for small residential posts, or standard concrete for larger gate posts and corner posts that carry more load — this tool works for either since you're specifying your own hole dimensions. It also adds a waste factor since post holes are rarely perfectly cylindrical and some concrete always spills at grade.", "formula": "Hole Volume = π × (Diameter/2)² × Depth. Post Volume ≈ PostWidth² × Depth. Net Volume per Post = Hole − Post. Bags = ceil((Net Volume × PostCount ÷ 0.6) × (1 + Waste%)).", "dateModified": "2026-09-06", "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=concrete-fence-post-calculator", "inputs": [ { "id": "holeDiameter", "label": "Hole diameter", "kind": "number", "hint": null, "default": 10, "unit": "in", "min": 4, "max": 24 }, { "id": "holeDepth", "label": "Hole depth", "kind": "number", "hint": null, "default": 24, "unit": "in", "min": 6, "max": 48 }, { "id": "postWidth", "label": "Post width", "kind": "number", "hint": null, "default": 4, "unit": "in", "min": 1, "max": 12 }, { "id": "postCount", "label": "Number of posts", "kind": "number", "hint": null, "default": 8, "unit": null, "min": 1, "max": 200 }, { "id": "wastePct", "label": "Waste factor", "kind": "number", "hint": null, "default": 10, "unit": "%", "min": 0, "max": 25 } ], "outputs": [ { "id": "bags", "label": "80lb bags needed (total)", "format": "number", "hint": null, "primary": true }, { "id": "netVolPerPost", "label": "Net concrete per post", "format": "decimal", "hint": "cu ft", "primary": false }, { "id": "totalCubicFeet", "label": "Total cubic feet", "format": "decimal", "hint": null, "primary": false }, { "id": "count", "label": "Posts", "format": "number", "hint": null, "primary": false } ], "worked_example": { "inputs": [ "Hole diameter: 10 in", "Hole depth: 24 in", "Post width: 4 in", "Number of posts: 8", "Waste factor: 10 %" ], "outputs": [ "80lb bags needed (total): 13", "Net concrete per post: 0.869", "Total cubic feet: 6.95", "Posts: 8" ] }, "how_to": { "title": "How to use this", "steps": [ "Enter hole diameter (in).", "Enter hole depth (in).", "Enter post width (in).", "Enter number of posts.", "Enter waste factor (%).", "Read your 80lb bags needed (total) on the right — it updates as you type.", "Hit Share to keep the scenario or send it to someone." ] }, "scenarios": [ { "name": "Conservative", "description": "Lower-end numbers — what if things land soft?", "values": { "holeDiameter": 6, "holeDepth": 14, "postWidth": 2.4, "postCount": 5, "wastePct": 6 } }, { "name": "Typical", "description": "Defaults — the most common real-world setup.", "values": { "holeDiameter": 10, "holeDepth": 24, "postWidth": 4, "postCount": 8, "wastePct": 10 } }, { "name": "Ambitious", "description": "Higher-end numbers — what if things really pop?", "values": { "holeDiameter": 16, "holeDepth": 38, "postWidth": 6.4, "postCount": 13, "wastePct": 16 } } ], "limitations": [ "Estimates assume standard, average conditions — local rules, pricing, and materials vary.", "Results are rounded for readability; add a buffer before ordering, booking, or committing.", "Double-check anything with a real cost attached against a local quote." ], "faq": [ { "q": "How deep should a fence post hole be?", "a": "A common rule is one-third of the post's above-ground height, or a regional frost-depth minimum, whichever is deeper — many residential fence posts use 24-30 inch holes for 6-8 foot fences." }, { "q": "Do I need to subtract the post's volume?", "a": "Yes, otherwise you'll over-order — the post physically displaces concrete in the hole, and for larger posts (4x4 or 6x6) that displacement is meaningful, especially in narrower holes." }, { "q": "Can I use quick-set concrete instead of standard mix?", "a": "Yes, quick-set (no-mix, pour-dry-then-water) concrete is popular for fence posts since it sets in 20-40 minutes without needing to hold the post plumb for hours, though it's typically sold in smaller 50lb bags." }, { "q": "Should every post use the same hole size?", "a": "No — gate posts and corner posts carrying more lateral load are commonly set in wider, deeper holes than standard line posts; run this calculator separately for each post type and add the results." } ], "related": [ "https://www.revenuelab.fyi/toolbox/concrete-bags-80lb-calculator", "https://www.revenuelab.fyi/toolbox/concrete-sonotube-piers-calculator", "https://www.revenuelab.fyi/toolbox/concrete-bags-60lb-calculator" ], "license": "CC-BY-4.0", "citation": "RevenueLab — Concrete for Fence Posts Calculator (https://www.revenuelab.fyi/toolbox/concrete-fence-post-calculator)" }