Fence Post & Rail Calculator

How to Use the Fence Post & Rail Calculator

Enter your total fence run length and post spacing in feet, how many horizontal rails run between each pair of posts, and how many bags of concrete you'll use per post footing. The calculator returns the number of posts, rails, and concrete bags needed for the whole run.

How the Calculation Works

The calculator divides your total fence length by the post spacing and rounds up to get the number of sections (spans between posts), then adds one to get the post count — a fence with 15 sections needs 16 posts, since posts sit at both ends of every section. Rails are calculated as sections × rails per section, since each section gets its own set of horizontal rails. Concrete bags are simply posts × bags per post footing, rounded up.

Example Calculation

A 120 ft fence at 8 ft post spacing, 3 rails per section, 2 bags of concrete per post: sections = ceil(120 ÷ 8) = 15. Posts = 15 + 1 = 16. Rails = 15 × 3 = 45. Concrete bags = 16 × 2 = 32.

Frequently Asked Questions

What post spacing should I use?

8 feet on-center is a common standard for wood fence panels and rail sections. Some pre-made panel systems come in fixed widths (like 6 or 8 ft), so it's worth checking your specific fencing material's spec before finalizing spacing.

How many rails does my fence need?

A basic 3-rail fence (top, middle, bottom) is common for privacy and picket fencing. Taller fences or those carrying heavier panels sometimes use 4 rails for extra rigidity — check your fence design or manufacturer's recommendation.

How much concrete does a fence post footing need?

It depends on the post size and hole depth, but 2 bags of 60 lb pre-mix per post footing is a common rule of thumb for standard residential fence posts set about 2 feet deep. Taller fences or windier locations may need larger footings.