Price Your Fence Before You Dig the First Hole

A wood fence looks simple until you stand in the lumber aisle trying to remember whether a 100-foot run needs 13 posts or 17 — and whether that changes how many pickets, rails, and bags of concrete to load into the cart. Guess wrong and you’re either making a second trip or storing warped boards all winter.

Need a price estimate? Try our Fence Cost Calculator.

This free fence calculator turns one measurement — your total fence length — into a complete material list: posts, pickets sized to your exact picket width and gap, horizontal rails, the post length to buy, and concrete bags per post based on your actual hole size. It assumes a straight picket-fence run, the most common DIY fence project.

How to Use This Calculator

1. Measure the fence line. Measure the total run in linear feet with a tape or measuring wheel. Subtract the width of any gates — each gate gets its own extra post and hardware.
2. Enter the fence height. Six feet is the standard privacy height. The calculator uses it to recommend the post length to buy.
3. Choose post spacing. Eight feet is the standard for wood fences; six feet gives a sturdier fence in windy or heavy-snow areas.
4. Set picket width and gap. A standard 1×6 picket is 5.5 inches wide. Use a 0 gap for a full-privacy fence, or up to an inch or two for a spaced picket look.
5. Pick rails per section. Two rails suit fences up to 5 feet; choose three rails for 6-foot and taller fences so pickets can’t bow.
6. Size your concrete. Enter your planned hole diameter and depth, then pick your bag size (50, 60, or 80 lb). The calculator works out bags per post from the real hole volume.
7. Calculate and shop the list. The results show posts, sections, pickets, rails, and total concrete bags — plus how the numbers were derived so you can sanity-check them.

What Is a Fence Calculator?

A fence calculator is a material takeoff for fencing: it converts the length of your fence line into quantities of posts, pickets, rails, and concrete. Where a generic “how much fence” guess stops at linear feet, a real takeoff accounts for the geometry of the build — posts come one-per-section plus one end post, pickets fill each section edge to edge, and every post sits in a concrete-filled hole with its own volume.

The tricky part is that these quantities interact. Wider post spacing means fewer posts and less concrete, but more pickets per section and longer rails. A wider picket with a bigger gap means fewer pickets overall. This calculator keeps all of those relationships consistent, so the picket count always matches the section count, and the concrete math always uses your hole size — not a one-size-fits-all guess of “two bags per post.”

The Formula (With a Worked Example)

Worked example: a 100 ft run, 8 ft spacing, 6 ft tall, 5.5 in pickets with a 0.5 in gap, 2 rails per section, 10 in × 24 in post holes, 50-lb concrete bags.

• Sections = ⌊100 ÷ 8⌋ = 12 (covers 96 ft; 4 ft left for a short final section or gate)
• Posts = 12 + 1 = 13
• Pickets per section = ⌈96 ÷ (5.5 + 0.5)⌉ = 16 → 192 pickets total
• Rails = 2 × 12 = 24 (8-ft rails)
• Hole = π × 5² × 24 ≈ 1,885 in³; minus the 4×4 post ≈ 294 in³ → ≈ 0.92 ft³ per post → ⌈0.92 ÷ 0.375⌉ = 3 bags → 39 bags total
• Post length = 6 ft + 2 ft buried = 8-ft posts

Enter these numbers in the calculator above and you will get exactly 13 posts, 192 pickets, 24 rails, and 39 bags of concrete.

Tips for an Accurate Fence Estimate

• Call 811 before you dig. In the US, dial 811 a few days ahead to have underground utilities marked — it’s free and legally required in most states. Striking a line is far more expensive than any material miscalculation.
• Bury one-third of the post. A 6-foot fence wants 2 feet of post underground. In cold climates, dig below the frost line or frost heave will push posts up over winter.
• Use 3 rails on tall fences. Two rails are fine up to about 5 feet, but 6-foot pickets fastened to only two rails can bow and warp within a season. The third rail is cheap insurance.
• Keep 5% spare pickets and rails. Lumber arrives with the occasional warped or split board. Spares from the same batch match better than a later purchase.
• Crown the concrete above grade. Slope the concrete slightly away from the post so water drains off instead of pooling against the wood — this alone can add years to a post’s life.
• Plan gates separately. Each gate needs its own posts (usually beefier, 6×6), hinges, and a latch. Subtract the gate width from your run length, then add the gate materials on top of the calculator’s list.

How Deep Should Fence Posts Be? The One-Third Rule and the Frost Line

Every post-depth rule in fencing comes back to one ratio: bury one-third of the post’s total length. A 6-foot fence therefore needs an 8-foot post — 6 feet above ground, 2 feet below. Shallow posts are the number one cause of fences that lean within a few winters.

Two adjustments matter. First, in cold climates the bottom of the hole must sit below the local frost line; a post whose base freezes in saturated soil gets jacked upward a little more each winter. Second, pour a 4 to 6 inch gravel base in the bottom of each hole before the post goes in — it drains the water that would otherwise pool around the buried end and rot it. Dig the hole about 6 inches deeper than the post’s buried length to make room for it.

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