Fence Calculator
Posts are the length divided by the spacing, rounded up, plus one post for the end. Rails are the sections times the rails you want on each section. Pickets are the length divided by the picket width plus the gap. Concrete is a full cylinder per post, and the post is not subtracted. Bags stay at 0 until you type a bag yield.
Last reviewed: 2026-10-28 · How we calculate
How we calculate
Posts = ceil(length ÷ spacing) + 1. Sections = posts − 1. Rails = sections × rails per section. Pickets = ceil(length ÷ (picket width + gap)). Concrete per post = π × radius² × depth, with radius half the diameter. Total concrete = that cylinder × posts. Bags use litres per bag only when the field is above zero.
Worked example
A 100 ft run at 8 ft spacing has 14 posts. Holes are 36 in deep. Bags use the form’s bag yield.
Posts, pickets, and the concrete in the holes
A straight garden fence is posts, rails, pickets, and a hole full of concrete. This page counts the posts at both ends, the rails you asked for, and the pickets along the run. Concrete volume is the hole, with the post still in it. Bags stay at 0 until you type a yield. An 80 lb QUIKRETE concrete mix bag is about 0.60 cubic feet, the figure already cited on the concrete page, if that is the bag you are buying.
Measuring a fence run
A straight fence is posts at both ends and at every spacing in between. Ten metres divided by 2 is 5, and 5 plus 1 is 6 posts. The sections are one fewer than the posts, so 5 sections. Two rails on each section is 10 rails. If the length is not an even multiple, the last space is shorter and the post count still rounds up, so you do not finish the run without an end post. A corner shared by two runs is counted twice if you add the two runs blindly. Subtract one post for each shared corner after you add the runs.
How the run becomes posts and pickets
Pickets march along the length. A 100 mm picket with no gap on a 10 m run is 100 pickets. A 10 mm gap makes the module 0.11 m and the count 91, because the gap occupies space that a picket does not have to fill. Use the cover width you will see, in feet, or metres on the metric toggle. Rails are only the count you asked for. The page does not choose two rails or three. Concrete is the post-hole cylinder repeated. Diameter 200 mm and depth 600 mm is pi times 0.1 squared times 0.6, about 0.0188 cubic metres for one hole, and six holes are 0.11 cubic metres after two-decimal rounding. The post itself stays in that volume.
Ordering fence concrete by the bag you have
Bags are deliberately blank until you type litres. The concrete page cites an 80 lb QUIKRETE yield of about 0.60 cubic feet, checked 24 October 2026, as 16.99 litres, and you can type 16.99 here if that is your bag. Do not type it just to see a number. Hole depth starts at the form’s inch default so the cylinder is not zero. It is not a frost-line rule and not a building-code minimum. Gravel in the bottom of the hole is not removed from the concrete. If you will place 100 mm of gravel first, shorten the concrete depth by that 100 mm.
Checking a fence order
Gates, slopes, and panels that are sold as a 1.8 m leaf are outside the picket division. A panel fence may not need pickets at all. Set the picket width to 0 and the picket count stays 0, then order panels as sections. The page will not price timber or concrete. Take the counts to the yard, and take the cubic metres to the concrete page if you want ready-mix rounded to the next quarter yard.
Fence fields and starting values
Fence length starts at 100 ft. Fence length in feet. Switch to m / cm for metres. Post spacing starts at 8 ft. Post spacing in feet. Switch to m / cm for metres. Rails per section starts at 2. How many horizontal rails you will fix between two posts. Two is a common starting count, not a rule. Picket width starts at 4 in. Picket width in inches. Gap between pickets starts at 0.5 in. Gap between pickets in inches. Hole diameter starts at 10 in. Hole diameter in inches, or millimetres on the metric toggle. Hole depth starts at 36 in. Hole depth in inches, or millimetres on the metric toggle. 80 lb bag yield starts at 0.6 cu ft. 0.60 cu ft matches the QUIKRETE 80 lb Concrete Mix listing checked on 24 October 2026. Edit it if your bag differs.
Fence posts and pickets for a straight run
Post spacing is 8 ft, pickets are 4 in with a 0.5 in gap, and each hole is 10 in by 36 in. Bag count is left off because the form does not assume a bag yield.
| Run | Posts | Pickets | Concrete |
|---|---|---|---|
| 50 ft | 8 | 134 | 0.37 m³ |
| 100 ft | 14 | 267 | 0.65 m³ |
| 150 ft | 20 | 400 | 0.93 m³ |
Both ends are included. A corner post is an extra you add. Concrete is the full hole, post included.
Common mistakes
- Forgetting the end post. The formula adds one after the divisions.
- Subtracting the post from the hole.
- Using a bag yield this page did not ask you to type.
- Counting a corner twice by running each leg with two end posts and not removing the shared post.
- Entering picket width in millimetres in a metre field.
- Treating 600 mm as a required hole depth.
Frequently asked questions
How many fence posts do I need?
Divide the length by the spacing, round up, and add one. Ten metres at 2 m spacing is 6 posts.
How many pickets?
Divide the length by the picket width plus the gap, and round up.
How much concrete per post?
A full cylinder. Six holes of 200 mm by 600 mm are 0.11 m³ together.
Does this include gates?
No. A gate replaces pickets and may add posts. Measure the gate opening out of the length or add the hinge posts yourself.
Why are bags zero?
Because litres per bag starts at 0. Use the concrete calculator if you want the cited 80 lb yield.
Is the spacing a code rule?
No. It is the spacing you intend to build.