A fence is a row of post holes with a budget attached. Enter the fence length and post spacing for the post count (ends included) and the total concrete for the whole run.
Fence Post Calculator
Posts = spaces + 1, a 100 ft fence at 8 ft spacing has 13 spaces and 14 posts. Corner and gate posts are extra-strong holes; add their count mentally to the bag total, or run them through the Post Hole Calculator at their bigger size.
For the whole fence
Wood fence posts typically space at 6–8 ft; chain-link at 8–10 ft. Where the run turns a corner or meets a gate, those posts take bigger, deeper holes than line posts.
A fence post calculator divides the fence length by the spacing, rounds up to whole spaces, and adds one end post, then multiplies the per-hole concrete by the post count. A 100 ft fence at 8 ft spacing needs 14 posts and, with 12 in × 3 ft holes, about 56 bags of concrete in total. Enter your run above.
How to Calculate Fence Posts and Concrete
Fence math has two traps that catch everyone once: the posts are always one more than the spaces, and the concrete is always more than ‘a couple of bags a hole’. A 100 ft fence is a small production, dozens of holes, a pallet’s worth of bags, and it deserves the same planning as any pour. This fence post calculator runs the whole line: posts, spaces, bags per hole and the total, with the post’s own displacement subtracted.
The Formula
Posts = spaces + 1
Total bags = posts × bags per hole (hole cylinder − post volume, ÷ 0.60 ft³ per bag)
Rounding spaces UP shortens the actual spacing slightly (100 ft ÷ 13 spaces = 7.7 ft), which is the safe direction for fence strength and rail lengths. The per-hole math is the Post Hole Calculator’s: hole volume minus the post’s below-ground volume, with a 10% waste allowance built into the bag count.
Worked Example: 100 ft Fence, 8 ft Spacing, 12 in × 3 ft Holes
Spaces = 100 ÷ 8 = 12.5 → 13. Posts = 14. Per hole: 2.10 ft³ → 4 bags. Total bags = 14 × 4 = 56, which is 1.20 yd³ with waste, two-thirds of a pallet of 80 lb bags (about 5,000 lb of material to move and mix). That total is the number that decides hand-mixing versus a mixer rental.
Posts per Fence Length by Spacing
| Fence length | 6 ft spacing | 8 ft spacing | 10 ft spacing |
|---|---|---|---|
| 25 ft | 6 posts | 5 posts | 4 posts |
| 50 ft | 10 posts | 8 posts | 6 posts |
| 100 ft | 18 posts | 14 posts | 11 posts |
| 150 ft | 26 posts | 20 posts | 16 posts |
| 200 ft | 35 posts | 26 posts | 21 posts |
Counts include both end posts for a single straight run. Every corner adds a post, every gate adds two heavier ones, and a run broken by a house wall uses the wall as an end. Sketch the layout and mark corners and gates before ordering, the table is for straight runs.
Where Fence Concrete Really Goes
The per-hole allowance (10%) covers bellied holes and crowning. Fence work adds its own losses: the hole that hits a rock and gets dug wider, the corner hole that becomes a small excavation, the bag that splits in the wheelbarrow. On runs over 20 posts, experienced crews order one extra bag per five holes beyond the count, it is cheaper than the mid-job store run and leftover bags return easily when bought by the pallet.
How to Measure and Calculate: Step by Step
- Measure the full fence line, marking corners, gates and ends.
- Choose spacing by fence type: 6–8 ft wood, 8–10 ft chain-link.
- Set hole diameter and depth (frost line) for your area.
- Enter the run above; note posts, bags per hole and the total.
- Add corner/gate holes separately at their larger size if they differ.
Worked Example 2: 50 ft Garden Fence, 6 ft Spacing
Spaces = 50 ÷ 6 = 8.33 → 9. Posts = 10. At 12 in × 3 ft holes: 4 bags per hole → 40 bags total (0.86 yd³). Tightening spacing from 8 ft to 6 ft on this short fence added 2 posts and 8 bags, on a 200 ft fence the same change adds 9 posts and 36 bags, which is the real price of the stronger spacing choice.
Common Quantities at a Glance: Cheat Sheet
| Job / quantity | Result |
|---|---|
| Per 100 ft at 8 ft spacing | 14 posts |
| Per 100 ft at 6 ft spacing | 18 posts |
| Bags per standard hole (12 × 3 ft) | 4 × 80 lb |
| 100 ft fence, total bags | 56 bags · 1.20 yd³ |
| 50 ft fence at 6 ft spacing | 10 posts · 40 bags |
| Gate/corner holes | Size separately, usually bigger |
Practical Tips From the Job
Set corners and ends first, pull a string line, and set line posts to the string, a fence is judged by its straightness from the street. Work in production order: dig all holes, set and brace all posts, then mix and pour in one pass. Crown each hole’s concrete and slope it away from the post so water sheds instead of pooling at the wood.
Common Mistakes to Avoid
- Counting spaces and ordering that many posts (one short, every time).
- Planning bags by folklore instead of per-hole volume.
- Setting line posts before the corners are in and strung.
- Using line-post hole sizes for gate posts.
- Pouring posts without bracing and discovering the lean at rail time.
What It Costs and How to Order Smart
For the 100 ft example: 56 bags ≈ $336 at $6, plus posts, rails and pickets, run the bags through the Bag Cost Calculator if the run is long, because at 1.20 yd³ a delivered mini-load or a mixer truck starts competing. Gate and corner upgrades (6×6 posts, 16 in holes) add a few bags each; price them as the separate line they are.
Who Uses This Calculator?
Builders fencing a lot use the post count for take-off. Contractors quote fence work per foot from these totals. Engineers meet fences at property lines and pool codes, spacing and depth are their language. Architects set the fence line on the plan, and homeowners get the three numbers the whole job hangs on: how many posts, how many bags, how much it all weighs.
Fence Post Calculator FAQs
How many fence posts do I need for 100 feet?
At 8 ft spacing: 100 ÷ 8 = 12.5, round up to 13 spaces, plus one end post = 14 posts. At 6 ft spacing it is 18 posts; at 10 ft, 11 posts. Corners and gates add posts beyond the straight-run count, sketch the layout and add one per corner and two per gate opening.
How much concrete do I need for a fence?
Per standard hole (12 in diameter, 3 ft deep, 4×4 post): 2.10 ft³, or 4 × 80 lb bags with allowance. The 100 ft, 14-post example therefore needs 56 bags (about 1.20 yd³ with waste). Longer fences or bigger holes scale directly, the per-hole figure is the multiplier everything hangs on.
What is the best fence post spacing?
Six to eight feet for wood privacy fences (8 ft matches rail and panel sizes; 6 ft is stronger in wind), 8–10 ft for chain-link line posts with a top rail. Wider spacing saves posts and concrete, about 4 posts and 16 bags per 100 ft going from 6 to 8 ft, and costs stiffness. Wind exposure and fence height argue for the tighter end.
How deep should fence post holes be?
Below the frost line, and as a field rule about one-third of the post’s above-ground height plus 6 in of base, a 6 ft fence typically lands at 2.5–3.5 ft of depth depending on climate. Your local code’s frost depth is the floor. Depth figures entered here should be your code depth, not a national average.
Do corner and gate posts need more concrete?
Yes, they carry the fence’s tension and the gate’s swinging load. Common practice upsizes them (6×6 posts, 14–16 in holes, sometimes deeper), which the Post Hole Calculator counts at roughly 6–8 bags per hole instead of 4. Budget them as a separate line so the line-post math stays clean.
Can I set fence posts without concrete?
Alternatives exist, compacted gravel, crushed stone, foam systems and driven posts, and each has its place, especially where future removal matters or drainage is extreme. Concrete remains the default for strength and familiarity. If you use compacted stone instead, the hole volumes on this page still tell you how much stone each hole swallows.
How long should fence posts cure before building the fence?
With standard mixes, keep rails and pickets off for at least 24–48 hours and gates for several days; fast-setting products state shorter times on the bag. The posts feel solid early because the hole walls brace them, the concrete’s own strength is what resists the first wind load, and it is still young on day one.
Why did my fence need more bags than calculated?
Oversize holes are the usual cause, a dug diameter 2 in over plan adds roughly 35–40% per hole at the 12 in size. Rocks, roots and corner excavations add more. Measure a few dug holes before mixing, adjust the diameter input, and the total re-forecasts itself for the rest of the run.
How accurate is this fence post calculator?
Post counts are exact for a straight run (spaces rounded up, plus one). Concrete totals carry the per-hole geometry and a 10% allowance, rounded up per hole, the way bags are actually opened. Corners, gates and problem holes are the variance; count them at their true sizes and the total lands within a bag or two on typical runs.
Related Calculators
Sources used for standards and conversions: National Ready Mixed Concrete Association (NRMCA) guidance on ordering and yield; American Concrete Institute (ACI) practice for mix and placement; Portland Cement Association (PCA) design and control guidance; US manufacturers’ printed yields (80 lb bag = 0.60 ft³). Depths, sizes and spacings set by your local building code govern wherever they differ from the general figures here.
Disclaimer: Results are estimates for planning and ordering. Confirm quantities with your supplier before ordering, and have structural work, footings, walls, columns, beams and anything load-bearing, checked by a licensed engineer.