How the calculation works
The calculator converts run lengths to meters, subtracts gate openings, divides usable run by maximum post spacing, and rounds up to sections. It counts endpoints, shared starts, and declared gate posts explicitly. Rails equal sections times rails per section. Optional pickets use width plus gap, and concrete uses net post-hole volume divided by explicit bag yield.
US example
A straight 100 ft run with maximum 8 ft spacing requires 13 sections and 14 line posts before gate or corner adjustments. At two rails per section, it needs 26 rails.
Metric example
A straight 30 m run with maximum 2.4 m spacing also requires 13 sections and 14 line posts before topology adjustments. At two rails per section, it needs 26 rails.
Start with fence topology
A single straight run has one more line post than sections. Connected runs may share an endpoint, while gates and corners can require additional posts. Advanced mode makes these assumptions explicit instead of silently applying one rule to every layout.
Spacing is treated as a maximum
The default is 8 ft, displayed as 2.4 m in metric mode. The engine divides usable run length by that maximum and rounds the number of sections up. Actual section widths can therefore be shorter. Choose spacing only after checking the fence system, height, loads, soil, local requirements, and installation instructions.
Rails, pickets, and concrete
Rails are the number of sections multiplied by rails per section. Optional pickets are based on usable run divided by picket width plus gap, followed by the selected extra allowance. Post-hole concrete uses cylindrical hole volume minus the embedded post volume, multiplied by the post count, then rounded by the product’s explicit bag yield.
Before any excavation, identify property and permit constraints and contact the applicable utility notification service for the project location. The linked DigAlert source is a California example, not a substitute for local requirements elsewhere.
Limitations
- Spacing in this calculator is a maximum planning input, not a structural recommendation for wind, soil, height, material, or local code.
- Property lines, permits, easements, utilities, frost, grade, drainage, gate loads, and manufacturer details require separate confirmation.
- Corners, connected runs, gates, and shared endpoints must match the real layout or the post count can be wrong.
Frequently asked questions
Why does maximum post spacing round sections up?
Rounding up keeps every calculated section at or below the entered maximum spacing instead of stretching the final section beyond it.
How are gate posts counted?
Advanced mode subtracts the gate opening from usable fence length and adds the declared extra posts for each gate. Confirm the gate system details.
Does the concrete option choose a safe footing size?
No. Hole and post dimensions are visitor inputs. Local conditions, code, frost, wind, fence height, and manufacturer requirements govern real footings.
Sources
Sources support unit conventions, product variability, and project limitations. They do not endorse this calculator.