How much fencing do I need?

People type this into search every day: fence calculator posts and panels.

The count starts from the run you measure, the bay you plan to build, and the gates you want. Rails, post depth, and wind load are a different drawing. This page follows the fence material calculator.

Bays, then one extra post, then the bags you type

The calculator assumes a straight, level line. It also treats a gate as one extra post, and it treats the gate width as one bay. It does not subtract the gate from the panel count.

bays = ceiling of (fence length ÷ panel width)

posts = bays + 1 + gates

bags = ceiling of (posts × bags per post)

Spacing is length ÷ bays. On a US display that spacing is shown in feet. The inputs stay in metres.

The two bags in the default are a number you type. They are not a code minimum. The calculator’s note says to confirm depth, wind load, utilities, and local rules before you dig. The concrete volume post is the cubic measure of a pour. This fence tool never converts a hole into cubic metres. It multiplies posts by the bag count you entered.

A deck rail is a different order. The decking post counts board rows. The board feet post is lumber volume. Neither one counts fence bays.

Example 1: the published 32 m run

Here are the calculator defaults:

• length: 32 m
• panel or bay width: 1.8 m
• gates: 1
• concrete per post: 2 bags

Bays: ceiling of 32 ÷ 1.8 = ceiling of 17.78 = 18

Posts: 18 + 1 + 1 = 20

Bags: ceiling of 20 × 2 = 40

Spacing: 32 ÷ 18 = 1.78 m, which displays as 5.83 ft

Eighteen panels at 1.8 m are 32.4 m of panel width. That is 0.4 m past the 32 m you typed, because the ceiling added a partial bay. The gate is still an extra post on top of those 18 panels. The formula does not remove a panel to make room for the gate.

Example 2: an 8 m garden run, one bag a post

• length: 8 m
• panel: 1.8 m
• gates: 1
• concrete: 1 bag

Bays: ceiling of 8 ÷ 1.8 = ceiling of 4.44 = 5

Posts: 5 + 1 + 1 = 7

Bags: 7 × 1 = 7

Spacing: 8 ÷ 5 = 1.6 m, displayed as 5.25 ft

Five bays on 8 m looks generous until you do the division. Four panels cover 7.2 m, which is 0.8 m short of 8 m, so the ceiling adds a fifth. The fifth panel is why a short garden does not scale down from the 32 m run in a straight line. 8 ÷ 32 of 18 bays would be 4.5, and the tool will not order half a bay.

Example 3: a 60 m boundary with two gates

• length: 60 m
• panel: 1.8 m
• gates: 2
• concrete: 2 bags

Bays: ceiling of 60 ÷ 1.8 = ceiling of 33.33 = 34

Posts: 34 + 1 + 2 = 37

Bags: 37 × 2 = 74

Spacing: 60 ÷ 34 = 1.76 m, displayed as 5.79 ft

Thirty-four panels cover 61.2 m. You are buying 1.2 m of panel past the tape. The two gates add two posts and four bags. They do not add two bays, and they do not remove two bays. Set the gate count to the gates you will hang, then check the panel total against the openings those gates occupy. Example 7 walks that check on the default run.

Example 4: what if I change only the panel width

Keep the 32 m length, the one gate, and 2 bags a post.

The 1.2 m bay: ceiling of 32 ÷ 1.2 = ceiling of 26.67 = 27. Posts: 27 + 1 + 1 = 29. Bags: 58. Spacing: 32 ÷ 27 = 1.19 m, displayed as 3.89 ft.

The 2.4 m bay: ceiling of 32 ÷ 2.4 = ceiling of 13.33 = 14. Posts: 16. Bags: 32. Spacing: 32 ÷ 14 = 2.29 m, displayed as 7.5 ft.

Moving from the 1.8 m default to 1.2 m adds 27 − 18 = 9 panels, 9 posts, and 18 bags. Moving to 2.4 m drops 4 panels, 4 posts, and 8 bags. A wider bay is a smaller order only when the ceiling still covers the run. The next example is a length where a few centimetres flip that ceiling.

Example 5: a length that divides evenly, and one that does not

Panel width stays 1.8 m. Gates stay at 0. Concrete stays at 2 bags, so the bag count is twice the posts.

An 18 m run divides evenly.

Bays: 18 ÷ 1.8 = 10 exactly

Posts: 10 + 1 + 0 = 11

Bags: 22

Spacing: 1.8 m, displayed as 5.91 ft

Ten panels cover 18.0 m. There is no leftover bay.

Add 0.1 m, to 18.1 m.

Bays: ceiling of 18.1 ÷ 1.8 = ceiling of 10.06 = 11

Posts: 12

Bags: 24

Spacing: 18.1 ÷ 11 = 1.65 m, displayed as 5.40 ft

One extra tenth of a metre adds a whole panel, a post, and two bags. Eleven panels cover 19.8 m, so most of that eleventh panel is past the tape. If the real run is 18.0 m and the tape was generous, you can stay on 10 panels. If the posts have to reach a corner at 18.1 m, the ceiling is the panel you need.

Example 6: a corner is two runs

The formula is one straight line. An L-shaped yard is two of those lines that share a corner post. Run each side, then decide whether that corner is one post or two.

Side A, 12 m, no gate, 2 bags:

Bays: ceiling of 12 ÷ 1.8 = ceiling of 6.67 = 7

Posts: 7 + 1 = 8

Bags: 16

Spacing: 5.62 ft

Side B, 8 m, one gate, 2 bags:

Bays: ceiling of 8 ÷ 1.8 = ceiling of 4.44 = 5

Posts: 5 + 1 + 1 = 7

Bags: 14

Spacing: 5.25 ft

Added as two separate orders: 12 panels, 15 posts, 30 bags.

One straight 20 m run with the same gate and the same 2 bags:

Bays: ceiling of 20 ÷ 1.8 = ceiling of 11.11 = 12

Posts: 12 + 1 + 1 = 14

Bags: 28

Spacing: 5.47 ft

The panel count matches, 12 and 12. The post count does not. The two runs each include the corner, so the shopping list has one post too many if that corner is a single hole. Drop that shared post and you are at 14 posts and 28 bags, the same post and bag totals as the straight 20 m line. The tool will not drop it for you. Measure each straight side, add the results, and subtract one post for each corner the two sides already share.

Example 7: the common mistakes

Start from Example 1: 18 bays, 20 posts, 40 bags.

Posts equal to the bay count

18 posts × 2 bags = 36 bags. You are short the end post and the gate post. That is 2 posts and 4 bags under the tool.

Posts equal to bays plus one, with the gate left out

19 posts and 38 bags. That is the 32 m run with the gate field set to 0. The gate post, and its two bags, are missing. The panel count stays 18 either way.

Skipping the ceiling

32 ÷ 1.8 = 17.78. Seventeen panels cover 30.6 m, which is 1.4 m short of the tape. The tool’s 18 panels cover 32.4 m. The difference is one panel, one post, and two bags.

Buying the panels and also a full extra bay for the gate

The assumption on the calculator says the gate width is treated as one bay. The arithmetic still returns 18 panels for 32 m, and it does not delete one of them when you type a gate. Eighteen panels are already 32.4 m. If the gate opening replaces one of those bays, the panel order is one bay high and the post count is the one that included the gate. Walk the layout with the gate opening marked before you treat 18 as the number of infill panels to pick up.

Leaving the bag field at 2 when the hole only needs 1 is the same kind of miss. Example 2 is that 8 m run at 1 bag: 7 bags, against 14 bags if you had left the default at 2.

Example 8: a run shorter than one panel, and a line with four gates

A 1.5 m run, a 1.8 m panel, no gate, 2 bags:

Bays: ceiling of 1.5 ÷ 1.8 = ceiling of 0.83 = 1

Posts: 1 + 1 + 0 = 2

Bags: 4

Spacing: 1.5 m, displayed as 4.92 ft

The result line reads 1 panels. One bay is wider than the run, and you still need two posts to hold it. There is no zero-panel answer for a positive length.

Back on the 32 m default, change only the gates, from 1 to 4.

Bays stay 18. Spacing stays 5.83 ft.

Posts: 18 + 1 + 4 = 23

Bags: 23 × 2 = 46

Each added gate is one post and two bags. It is not another 1.8 m of panels.

The same 8 m garden from Example 2, with the bag field set to 1.5 instead of 1:

Posts stay 7. Bags: ceiling of 7 × 1.5 = ceiling of 10.5 = 11.

A whole number of bags per post would have landed on 7 or 14. The ceiling is why 1.5 bags a post is 11 bags, not 10.5.

The steps are uneven because of the ceiling. From 8 m to 16 m you add 4 posts. From 16 m to 24 m you add 5. From 24 m to 32 m you add 4 again. A gate count that stays at 1 is inside every one of those totals.

The orders next to each other

Open the fence material calculator with one straight run in the length box. Split corners into separate runs and share the corner post by hand. If the same project has a deck, the decking material calculator counts those boards, and the concrete volume calculator is there when you know the hole size and want cubic metres instead of a bag count you typed. Post depth and the local rule for the fence line are still outside this bay count.