Fence Calculator (Posts, Rails, Pickets & Concrete)
Estimate the posts, rails, pickets or panels, and bags of concrete you need to build a fence from the run length, post spacing, picket size, and post-hole size. Metric and imperial.
13 bays; each post hole ≈ 29.5 L, total 14.6 ft³ of concrete. The hole is filled whole (buried post not subtracted), so this slightly over-orders. Deepen posts in soft ground, frost, or high wind.
How this works
A straight run is divided into bays between posts. The run needs one more post than bays to close each end:
sections = ceil(length / post spacing)
posts = sections + 1 + extra posts
rails = sections × rails per bay
pitch = picket width + gap
pickets = ceil(length / pitch) × (1 + waste)
hole = π × (diameter / 2)² × depth
concrete = posts × hole volumeAdd extra posts for corners, ends, and gate frames. In panel mode one pre-made panel fills each bay, so panels equal the number of sections and there are no separate rails or pickets. The concrete fills the whole hole and does not subtract the buried post, which leaves a small allowance for spillage.
Worked example
A 30 m run with posts at 2.4 m centres, 90 mm pickets with a 50 mm gap, 2 rails per bay, 250 mm × 600 mm post holes, 80 lb bags, 10% waste:
- sections =
ceil(30 / 2.4)= 13 → 14 posts - rails =
13 × 2= 26; pitch = 140 mm; pickets =ceil(30 / 0.14) × 1.10≈ 237 - hole ≈
π × 0.125² × 0.6= 0.0295 m³; concrete =14 × 0.0295≈ 0.41 m³ → 25 bags
Sources
- Post spacing, embedment depth, and concrete-per-hole guidance follow common residential fencing practice; confirm depth against local frost and wind requirements.
FAQ
How many fence posts do I need?
Divide the total run by your post spacing and round up to get the number of bays, then add one to close the far end. A 30 m fence with posts at 2.4 m centres has 13 bays and so needs 14 posts. Add extra posts for every corner, every free end, and each side of a gate, because those carry more load and are usually set deeper. This calculator does the arithmetic and adds your extra posts on top.
How far apart should fence posts be?
For most timber and panel fences, posts are set 1.8 to 2.4 metres (6 to 8 feet) apart on centre. Closer spacing gives a stiffer, stronger fence and is worth it in high wind or for tall privacy fences; wider spacing uses fewer posts but lets rails sag over time. If you are using pre-made panels, set the spacing to the exact panel width so each bay takes one panel without cutting.
How deep should fence post holes be?
A common rule is to bury about one third of the post's above-ground height, with a minimum of around 600 mm (2 feet) for a typical fence. Go deeper — 750 to 900 mm — for tall privacy fences, gate posts, corner posts, sandy or soft soil, and anywhere the ground freezes, where the hole should reach below the frost line. The hole diameter is usually about three times the post width. Always check your local building or wind requirements.
How much concrete do I need per fence post?
It depends on the hole size. The calculator works out the volume of each cylindrical hole from its depth and diameter, multiplies by the number of posts, and divides by the yield of the bag size you pick. As a guide, a 250 mm × 600 mm hole holds about 0.03 m³, which is roughly two 80 lb bags of pre-mix per post. It fills the whole hole without subtracting the buried post, so treat the result as a slight over-estimate that covers spillage and uneven digging.
How do I calculate the number of pickets?
Add the picket face width to the gap you want between pickets to get the spacing each picket occupies, then divide the total fence length by that figure and round up. Narrower pickets or smaller gaps mean more pickets; a butted privacy fence with no gaps needs the most. The calculator adds a waste allowance on top for cuts, splits, and the odd warped board. Rails (the horizontal stringers) are counted separately — usually two per bay, three for tall fences.
Does this include gates, caps, hardware, and paint?
No. The calculator estimates posts, rails, pickets or panels, and post-setting concrete. Gates and their hinges and latches, post caps, fixings such as nails or screws, gravel for the bottom of each hole for drainage, and any stain or paint are separate items. Add posts on each side of a gate opening using the extra-posts field, and buy fixings by the box and finish by the coverage rate on the tin.