Fence Calculator
Enter the total fence length, the number of straight runs and gates, and the post spacing to count posts, rails and pickets, plus the bags of concrete that go in the post holes.
Quick answer: 120 ft of 6 ft fence with 8 ft post spacing and one gate needs 17 posts, 45 rails and 288 pickets of 5.5 in with no gaps.
Sections = fence length ÷ post spacing, rounded up. Posts = sections + 1 to end an open run + 1 per gate. Rails = 2 per section for a 4 ft fence or 3 for a 6 ft fence. Pickets = fence length in inches ÷ (picket width + gap), plus 10%.
Example: 120 ft of 6 ft fence with 8 ft spacing and one gate is 15 sections, 17 posts, 45 rails and 288 pickets of 5.5 in with no gaps.
Method
How this calculator works
The layout rules come from a fence-picket manufacturer’s own calculator, and the post-hole sizes from a concrete maker’s data sheet. Post spacing, rails and allowances are yours to change.
Sections and posts
Post spacing is typically 6 or 8 ft on center; the calculator starts at 8 ft. Add one post for each section, one to end a run, and one for each gate. For a closed loop the end posts are not needed. Each corner starts a new run.
Sections = round up (Run length ÷ Post spacing)Posts = Sections + 1 per open run + 1 per gateRails
The manufacturer’s guide calls for 2 backer rails per section on a 4 ft tall fence, or 3 per section on a 6 ft tall fence. Pick the one that matches your fence in the options.
Rails = Sections × 2 (4 ft tall) or × 3 (6 ft tall)Pickets
Each picket takes its own width plus the gap beside it. Use actual widths, not nominal: a 1×6 picket is 5.5 in. The guide recommends adding 10% for culls and cuts; you can change it from 0 to 30%.
Pickets = round up (Length (in) ÷ (Picket width + Gap) × (1 + Allowance ÷ 100))Concrete per post hole
QUIKRETE’s Fast-Setting sheet says the hole should be 3 times the post diameter and as deep as half the post height above ground. The calculator subtracts the post itself, adds your allowance and divides by the bag yield. You can override the depth for frost or code.
Hole = π × (3 × Post width ÷ 24)² × Depth (ft)Concrete = Hole − (Post width ÷ 12)² × DepthBags = round up (Posts × Concrete × (1 + Allowance) ÷ Yield)Worked example: 120 ft of 6 ft tall fence, 8 ft spacing, one gate
Arithmetic checked3 rails per section, 5.5 in pickets with no gap and a 10% allowance, 4×4 posts (3.5 in actual) set 3 ft deep, 10% concrete allowance, 80 lb bags at 0.60 ft³.
| Step | Math | Result |
|---|---|---|
| Sections | 120 ÷ 8 | 15 |
| Posts | 15 + 1 end + 1 gate | 17 posts |
| Rails (6 ft tall fence) | 15 × 3 | 45 rails |
| Pickets | 1,440 in ÷ 5.5 = 261.8, × 1.10 | 288 pickets |
| Hole in one post (10.5 in wide, 3 ft deep) | π × (10.5 ÷ 24)² × 3 | 1.804 ft³ |
| Subtract the post | (3.5 ÷ 12)² × 3 | 0.255 ft³ |
| Concrete per hole | 1.804 − 0.255 | 1.549 ft³ |
| All 17 holes with 10% allowance | 1.549 × 17 × 1.10 | 28.96 ft³ |
| 80 lb bags (0.60 ft³ each) | 28.96 ÷ 0.60 = 48.3, round up | 49 bags |
| You would buy | 17 posts, 45 rails, 288 pickets, 49 bags of 80 lb concrete | |
Disclaimer
Results are planning estimates based on the dimensions and assumptions you enter. They are not engineering, structural or building-code advice. Product yields, densities and coverage vary by manufacturer, batch and site conditions. Check product labels, your supplier and your local building department before you order materials or start work. Read the full calculation disclaimer.
Accuracy
What affects your estimate
A fence is simple until the yard is not. These are the details that change the count.
Corners and runs
Each straight run needs a post at both ends. A fence with one corner is two runs. Entering it as one long run undercounts posts. The length is split evenly between the runs you enter, so a very uneven layout needs a closer look.
Gates
A gate adds a post, and gate posts are often heavier or doubled. Gate openings are not subtracted from the length, so pickets are slightly over-counted. Hardware is not included.
Slope
On a slope, stepped panels or racked rails use more material than a level run. The count assumes a level fence.
Post size, depth and frost
The hole follows half the above-ground height. Frost depth and local code can require deeper holes, so use the hole-depth override. Bag yield assumes QUIKRETE Concrete Mix #1101; a fast-setting mix can differ. Check your bag.
Check property lines, permits, height limits and your HOA first, and call 811 before you dig. This is a material estimate, not a design. Corner and gate posts, panel styles and gate hardware change the count.
Common mistakes
Counting sections as posts
Fifteen sections need at least sixteen posts, not fifteen. An open run has a post at each end, and every gate adds another.
Using nominal post and picket sizes
A 4×4 post is 3.5 in and a 1×6 picket is 5.5 in. Entering the nominal size changes the hole volume and the picket count.
Stopping at the half-height rule
The depth rule is a starting point. In cold climates the frost line, and in some places local code, sets a deeper hole.
Questions people ask
How many fence posts do I need for 100 feet?
At 8 ft spacing, 100 ÷ 8 = 12.5, so 13 sections. An open run adds one end post, so 14 posts, plus one for each gate.
How many rails per section does a fence need?
Two backer rails per section for a 4 ft tall fence, three for a 6 ft tall fence, per the Outdoor Essentials guide. If you buy rails or pickets by the board foot, the board foot calculator totals them.
How many pickets do I need?
Divide the fence length in inches by the picket width plus the gap, then add about 10%. For 120 ft of 5.5 in pickets with no gap, 1,440 ÷ 5.5 = 261.8, and 288 with 10% extra.
How much concrete does a 4×4 fence post need?
With a hole 3 times the post width and 3 ft deep, about 1.55 ft³ per post. That is 2.58 of the 0.60 ft³ bags of 80 lb mix, so 3 bags per post if you buy per hole. The guide on concrete per fence post adds 6×6 posts and a table by fence height.
Is 2 feet deep enough for fence posts?
The rule used here is half the height above ground: 2 ft for a 4 ft fence, 3 ft for a 6 ft fence. Frost depth and local code can require more, so enter your own depth when they do.
Related calculators and guides
Sources
Where the numbers come from
- Outdoor Essentials (via Lowe’s) Fence Calculator, Building With Pickets (posts, rails, pickets), accessed October 16, 2026.
- QUIKRETE Fast-Setting Concrete Mix #1004-60 data sheet (hole width and depth), accessed October 16, 2026.
- QUIKRETE Concrete Mix #1101 data sheet (bag yields), accessed October 16, 2026.