Introduction
This case study is hypothetical and illustrative. It describes a fictional fence project with assumed dimensions, soil, and prices — not a real job, client, or contractor. Its purpose is to show the complete estimating workflow end to end: counting posts, running the per-hole math, converting to an order, and budgeting. Replace every assumed number with your own measurements.
The Fence Post Concrete Calculator performs the per-hole calculation used throughout this example. The workflow around it — counting, configuring, ordering — is detailed in the how-to-estimate guide.
The Hypothetical Project
A homeowner plans a 240-foot cedar privacy fence forming three sides of a rectangular back yard (the house closes the fourth side). Assumptions for this illustration:
- Fence height 6 ft; 4×4 posts; 8-ft nominal spacing.
- Three straight runs: 80 ft, 80 ft, 80 ft, with 4 corner posts total (the two house-side ends count as end posts).
- One 4-ft walk gate → 2 gate posts, upgraded to 6×6 in larger holes.
- Loam soil, no rock; frost line 30 inches; local code allows 6-ft rear fences.
- Fast-setting 50-lb bags at $7 each (illustrative price); 0.375 ft³ yield per bag.
- 4-inch gravel base under every post.
Step 1: Count the Posts
Per run: (80 ÷ 8) + 1 = 11 posts. Three runs = 33 positions, but the 4 corners are shared between runs — counting per run double-counts them. Cleaner method: total line positions minus shared corners.
- Run A: 11 posts (2 corners + 9 line)
- Run B: 11 posts (2 corners + 9 line)
- Run C: 11 posts (2 corners + 9 line, with 2 of the “line” positions becoming gate posts)
Unique posts: 27 line posts + 4 corner posts + 2 gate posts = 33 posts total. (The two house-side end posts are counted among the corners here — each run’s terminal post gets the deeper corner treatment.)
Step 2: Define the Hole Configurations
Three configurations, each run through the calculator once:
| Configuration | Hole (dia × concrete depth) | Post | Gross | Post disp. | Net | +10% waste | Bags |
|---|---|---|---|---|---|---|---|
| Line post | 12 in × 32 in | 4×4 | 2.09 ft³ | 0.30 ft³ | 1.80 ft³ | 1.98 ft³ | 6 |
| Corner/end post | 12 in × 38 in | 4×4 | 2.49 ft³ | 0.35 ft³ | 2.14 ft³ | 2.35 ft³ | 7 |
| Gate post | 16 in × 38 in | 6×6 | 4.42 ft³ | 0.79 ft³ | 3.63 ft³ | 3.99 ft³ | 11 |
Notes on the inputs: concrete depth is dug depth minus the 4-inch gravel base (36−4=32 for line posts; the 30-inch frost line plus margin gives 42-inch dug depth, 38-inch concrete depth, for corners and gates). Check the gate math by hand: radius 0.6667 ft, depth 3.1667 ft → π × 0.4444 × 3.1667 = 4.42 ft³ gross; 6×6 displacement 0.25 × 3.1667 = 0.79 ft³; net 3.63 ft³; +10% = 3.99 ft³; ÷ 0.375 = 10.65 → 11 bags per gate post. Hand-verifying one configuration like this is worth the two minutes on any real project.
Step 3: Multiply Out
Using the corrected gate-post figure:
- Line posts: 27 × 6 = 162 bags
- Corner/end posts: 4 × 7 = 28 bags
- Gate posts: 2 × 11 = 22 bags
- Subtotal: 212 bags
- Contingency: +3 spare bags = 215 bags
Total concrete volume: 212 bags × 0.375 ft³ ≈ 79.5 ft³ ≈ 2.9 yd³ — confirming this is a bag job, not a truck job (see the cost guide for the bags-vs-delivery reasoning).
Step 4: Budget It
| Item | Quantity | Unit price (illustrative) | Cost |
|---|---|---|---|
| Fast-setting 50-lb bags | 215 | $7.00 | $1,505 |
| Drainage gravel 0.5 ft³ bags | 8 (33 holes ÷ ~4.5) | $5.50 | $44 |
| Auger rental, 2 days | 1 | $70/day | $140 |
| Stakes, string line, misc. | — | — | $40 |
| Total setting cost | $1,729 |
Per-post setting cost: $1,729 ÷ 33 ≈ $52 per post all-in (concrete, gravel, rental share). The concrete alone is $1,505 ÷ 33 ≈ $46 per post — inside the $36–$48 band from the cost guide, toward the top because of the deeper corner and gate holes.
Step 5: Schedule It (Illustrative)
At a DIY pace of 8 posts per day in loam (see the DIY vs pro guide):
- Day 0 (week before): 811 locate ticket, permit, HOA approval, material delivery.
- Day 1: Layout — string lines, mark all 33 hole positions, verify gate opening width.
- Day 2: Auger all 33 holes; place gravel bases.
- Days 3–6: Set posts — corners and gates first, then line posts (~8/day).
- Day 7+: Hang rails and pickets after the 24-hour cure.
What This Example Teaches
- Gate posts dominate the variance. Two gate posts needed 22 bags — as much as nearly four line posts. Lumping them in with line posts would have under-ordered by 10 bags.
- The gravel base changes every number. Subtracting 4 inches of gravel saved roughly half a bag per hole — 16 bags across the project — and bought drainage. Both effects are real; only one shows in the budget.
- Hand-checking caught an error. The gate-post arithmetic above contained a unit slip (38 inches treated as 3.8 ft) that changed the answer by 3 bags per post. Always verify one configuration by hand.
- Contingency is separate from waste. The 10% waste covered hole irregularity; the 3 spare bags covered the unknown unknowns. Both were needed conceptually; only one gets used physically.
Related Guides
- How to Estimate Fence Concrete — the counting method used here.
- Fence Concrete Cost Guide — pricing and budgets.
- Fence Post Concrete Complete Guide — the full how-to.
- Fence Concrete DIY vs Pro — pace and hiring comparisons.
- Fence Concrete Pre-Dig Checklist — the day-zero workflow.
Frequently Asked Questions
Is this case study based on a real fence?
No. It is explicitly hypothetical — fictional dimensions, prices, and soil — constructed to demonstrate the estimating workflow. Your numbers will differ; the method won’t.
How much concrete did the hypothetical fence need?
212 bags of 50-lb fast-setting mix (plus 3 spare), about 2.9 cubic yards total, for 33 posts — roughly $1,505 in concrete at the illustrative $7/bag price.
Why did the gate posts need so much more?
Bigger hole (16-inch vs 12-inch diameter) and deeper setting for the gate’s dynamic load. Volume scales with the square of the radius, so small diameter increases cost disproportionately.
How long did the hypothetical project take?
About 7 days DIY: 1 layout, 1 digging, 4 setting at ~8 posts/day, then rails and pickets after curing. Illustrative pace for loam soil.
Get Your Number
Run your own fence through the same five steps with the Fence Post Concrete Calculator: count by post type, configure each hole, multiply, budget, schedule. The hypothetical fence needed 215 bags and $1,729 in setting costs — yours will differ, but now you know exactly where every bag goes.
Disclaimer: This case study is entirely hypothetical and illustrative — all dimensions, prices, soil conditions, and timelines are assumed for demonstration. It is not a quote, a guarantee, or professional advice. Verify all requirements with local suppliers, your building authority, and (for structural questions) a licensed professional.
