Fence Calculator – Posts, Pickets, Rails & Concrete

Item	Quantity	Unit price	Cost
Posts	14 pcs	Price per pcs for Posts	–
Pickets	210 pcs	Price per pcs for Pickets	–
Rails	24 pcs	Price per pcs for Rails	–
Concrete bags	27 bags	Price per bags for Concrete bags	–
Estimated total	–

How to use the fence calculator

Choose Imperial or Metric.
Enter the total fence length, the post spacing, the number of gates and the gate width.
Choose rails and pickets or panels. For pickets, set the rails per section, picket width and gap.
Enter the post hole diameter, depth and the post width.
Enter the concrete per bag from the bag label.

How the estimate works

Sections = ⌈(length − gates × gate width) ÷ post spacing⌉. Posts = sections + 1 + gates. Pickets = ⌈fence length without gates ÷ (picket width + gap)⌉. Rails = sections × rails per section. Concrete = (π/4 × hole diameter² − post width²) × depth × posts. Bags = ⌈concrete ÷ bag yield⌉.

Worked examples

100 ft picket fence. Posts every 8 ft, one 4 ft gate: 12 sections and 14 posts. 3½ in pickets with 2 in gaps: 210 pickets. Two rails per section: 24 rails. 10 in holes 30 in deep around 3½ in posts: 0.6 yd³ of concrete, or 27 bags at 0.6 ft³ each.

30 m metric fence. Posts every 2.4 m, one 1 m gate: 13 sections and 15 posts, 208 pickets of 90 mm with 50 mm gaps, 26 rails, 0.46 m³ of concrete or 28 bags at 0.017 m³.

How to interpret the results

Buy posts and panels as counted, add a few spare pickets for breakages, and round concrete up to whole bags.

Tips and common mistakes

Locate underground services before digging.
Check boundaries and height limits; many councils and HOAs regulate fence height.
Set gate posts deeper or larger, because they carry more load.
Slope the concrete top away from the post to shed water.

Choosing post spacing

Closer posts make a stiffer fence but cost more in posts, holes and concrete. Prefabricated panels fix the spacing for you: use the panel width plus the post width. For picket fences, spacing is often set by the length of the rails you can buy so that each rail spans one section without joins. Try a couple of spacings in the calculator to see how the post and concrete totals change.

Assumptions and limitations

The fence is treated as straight runs on level ground. Stepped or racked fences on slopes need extra material. Retaining walls are structural and are not covered.

Frequently asked questions

How many fence posts do I need?

Divide the fence length minus gate widths by the post spacing and round up to get the number of sections; add one post to close the run, and one for each gate. 100 ft with one 4 ft gate at 8 ft spacing gives 12 sections and 14 posts.

How many pickets per section?

Divide the section length by picket width plus gap. With 3½ in pickets and 2 in gaps, an 8 ft section takes about 17½ pickets.

How much concrete per fence post?

Hole volume minus the post volume: (π/4 × hole diameter² − post width²) × depth. A 10 in hole 30 in deep around a 3½ in post holds about 1.15 ft³.

How many bags of concrete per post?

Divide the concrete volume by the yield printed on the bag. An 80 lb bag of pre-mix makes about 0.6 ft³, so a 1.15 ft³ hole takes about two bags.

How deep should fence posts be?

A common rule is about a third of the post height above ground, and below the frost line in cold climates. Follow local requirements and the fence supplier’s guidance.

Does it handle corners?

Each run is calculated as a straight line. For a fence with corners, run it once per side and subtract the shared corner posts.

Sources

NIST Guide to the SI, Appendix B — Conversion Factors — National Institute of Standards and Technology