Fence Calculator

Q: How many fence posts do I need?

For panel fencing, divide the total fence length by the panel width (typically 1.83 m) and add 1 for the final post. A 20 m fence with 1.83 m panels: 20 / 1.83 = 10.93, round up to 11 panels, plus 1 = 12 posts. For close-board fencing, posts are typically spaced at 2.4-3.0 m centres. Always check the panel or board manufacturer's recommendation for maximum post spacing. Add gate posts separately - these are usually heavier section and may need to be set in concrete to a greater depth.

Q: How deep should fence posts be set?

The standard rule is to bury one third of the total post length in the ground. For a 1.8 m high fence you need a 2.4 m post - 600 mm in the ground, 1800 mm above. For a 1.2 m fence, use a 1.8 m post - 600 mm in ground. In loose or sandy soil, or for corner or gate posts that take more load, increase the buried depth to 750-900 mm. Always set posts in concrete or use purpose-made metal post spikes where soil conditions allow.

Q: How much concrete do I need for fence post holes?

A typical post hole for a 75 x 75 mm or 100 x 100 mm post is dug to approximately 600 mm depth and 300 mm diameter. The volume of one post hole (minus the post) is approximately 0.042 m3. A 25 kg bag of postcrete or rapid-set concrete covers approximately 0.010-0.012 m3, so you need 3-4 bags per post hole. For a 12-post fence, that is 36-48 bags. Postcrete (just-add-water rapid-set) is popular for fence posts as it sets in 5-10 minutes without mixing.

Q: Do I need planning permission for a garden fence?

In England, under permitted development rights you can erect a fence up to 1 m high adjacent to a highway (road or footpath) and up to 2 m high elsewhere, without planning permission. These limits refer to the finished fence height. If you live in a listed building, a Conservation Area, or if your permitted development rights have been removed by condition, you will need planning permission. A fence over 2 m always requires permission. Party boundary fences between neighbours are also subject to the same rules - both neighbours should agree before erecting a boundary fence.

Q: What is the difference between close-board and panel fencing?

Panel fencing uses pre-assembled panels (typically 1.83 x 1.83 m) fixed between posts. It is quick to erect, cheaper, but less strong - panels can flex and warp in high winds and are harder to repair if damaged. Close-board fencing is built on-site using arris rails fixed between posts, with featheredge boards nailed overlapping onto the rails. It is stronger, longer-lasting, and can be built to exact dimensions, but takes more time and skill to erect. Close-board fencing is the preferred choice for exposed or windy sites.

Q: What waste allowance should I use for close-board fencing?

For close-board featheredge boards, allow 10% waste for cutting around post positions and trimming top and bottom. For arris rails, calculate the exact number of linear metres needed at two or three rails per bay (depending on height) and add one length for cutting waste. Gravel boards (horizontal boards at the base that protect the featheredge from ground contact) are typically 150 mm high and should be measured as one per bay. Use tanalised (pressure-treated) timber for all fence components - untreated softwood in contact with soil will rot within 2-3 years.

Posts, panels, rails, gravel boards - for lap panel, close board, picket, featheredge, and hit & miss fencing

Fence Style

Pre-made lap panels fixed between posts. The most common UK garden fence. Typically 1.8 m wide x 0.9-1.8 m tall. Simple and quick to erect.

Panel / Bay Width (m) Standard lap panel: 1.8 m. Trellis: 1.8 m.

Fence Height (m)

Arris Rails per Bay Lap panels: rails not separate. Close board / featheredge: 2 rails up to 1.5 m, 3 rails above.

Post Type

Post Burial Depth (m) Rule of thumb: 1/3 of total post length. Min 0.45 m for a 1.8 m fence.

Postcrete Bags per Post Typically 1-2 x 20 kg bags per post. Set to 0 for spikes or if dry-packed.

Include gravel boards 100 x 22 mm timber or concrete. Protects panel base from ground moisture.

Include post caps Protects post tops from water ingress. One per post.

Board / Rail Waste (%) Applied to close board / featheredge board quantity only.

Fence Sections

Each section is a straight run between corners. Corner posts are shared - the calculator accounts for this automatically.

Job Costing (optional)

Panel / bay cost each

Post cost each

Arris rail per metre

Gravel board per metre

Postcrete per bag

Post cap each

Labour cost

Rate x total length

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Results

Total Run
-
metres

Posts

inc. corners

Panels / Bays

panels

Arris Rails

linear metres

Section Breakdown

Section	Length	Bays	Posts	Rails (LM)	Gravel Board (LM)

Material List

Item	Quantity	Notes

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Frequently Asked Questions

How many fence posts do I need?

Panel fencing: divide fence length by panel width (typically 1.83 m) and add 1. A 20 m fence = 11 panels + 12 posts. Close-board: posts at 2.4-3.0 m centres. Add gate posts separately - these need heavier section timber and deeper setting.

How deep should fence posts be set?

Bury one third of total post length in the ground. 1.8 m fence: use a 2.4 m post (600 mm below ground). 1.2 m fence: use a 1.8 m post (600 mm below). In loose or sandy soil, or for corner and gate posts: increase buried depth to 750-900 mm.

How much concrete do I need for fence post holes?

A typical post hole (600 mm deep x 300 mm diameter) needs approximately 3-4 bags of postcrete (25 kg) per post. For 12 posts: 36-48 bags. Postcrete (rapid-set, just add water) is popular for fence posts - sets in 5-10 minutes without mixing.

Do I need planning permission for a garden fence?

In England, permitted development allows: up to 1 m high adjacent to a highway; up to 2 m high elsewhere - no planning permission needed. Exceptions: listed buildings, Conservation Areas, or where permitted development rights have been removed. A fence over 2 m always requires planning permission.

What is the difference between close-board and panel fencing?

Panel fencing: pre-assembled panels (typically 1.83 x 1.83 m) fixed between posts - quick, cheap, but less strong; panels flex in high winds. Close-board: arris rails fixed between posts with overlapping featheredge boards nailed on-site - stronger, longer-lasting, built to exact dimensions. Close-board preferred for exposed or windy sites.

What waste allowance should I use for close-board fencing?

Featheredge boards: 10% waste. Arris rails: calculate exact linear metres (two or three rails per bay) plus one length for cutting waste. Gravel boards: one per bay, 150 mm high. Always use tanalised (pressure-treated) timber for all components - untreated softwood in ground contact rots within 2-3 years.

UK Building Regulations Planning / Part A / BS 8300

Rear garden boundary Front boundary (highway) Security / commercial Pool / drop barrier Acoustic / noise barrier

Max height (no planning)2.0 m

Post depth (min)600 mm

Planning required above2.0 m

StandardGPDO / Part A

Rear garden boundary fences up to 2.0 m high are permitted development under the General Permitted Development Order (GPDO) and do not require planning permission. Posts must be set a minimum of 600 mm into the ground, or one third of the above-ground height for taller fences.

Fence Styles

Lap panel - pre-made panels slotted between or screwed to posts. Quick to erect. Standard size 1.8 m x 0.9-1.8 m. Less strong than close board.
Close board - featheredge boards nailed vertically to arris rails on the face of posts. Strong and long-lasting. Typically 3 rails above 1.5 m.
Featheredge - same as close board but boards vary in thickness (thin at one edge). Most common close board style.
Picket / paling - open-style fence with gaps. Decorative - typically 0.9-1.2 m tall for front gardens.
Hit & miss - boards alternate front and back face. Looks the same from both sides; wind passes through. Privacy screen without wind resistance issues.
Trellis - decorative lattice, often used as fence topper or garden divider. Not suitable as a boundary fence on its own.

Post Depth Guide

Fence height	Min burial	Post length
0.9 m	0.45 m	1.5 m
1.2 m	0.45 m	1.75 m
1.5 m	0.50 m	2.1 m
1.8 m	0.60 m	2.4 m
2.1 m	0.75 m	3.0 m

In soft ground, loose soil, or exposed sites add 100-150 mm extra burial depth.

Tips

Always start and end each section with a post - corners are shared between sections
Use pressure-treated timber throughout - UC4 rated for ground contact on posts
Set posts in Postcrete (fast-set concrete) or dry-mixed concrete - prop plumb while setting
Gravel boards protect the panel or board base from ground moisture - add 50-100 mm clearance
For close board / featheredge, start with a full board at one end and trim the last board to fit
Cap all post tops - uncapped end grain is the biggest cause of post rot

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