Picket Fence Calculator UK: Materials & Cost

A picket fence calculator for the UK works out how many pickets, rails, and posts you need, plus the total material cost, based on your fence line length, picket width and spacing, and post spacing. You enter the length of the run in metres, the picket width and gap in millimetres, and the post spacing in metres; the calculator returns the number of pickets, the number of posts, and the total cost for each component. This guide explains the calculations, the common UK sizes, and the pitfalls that lead to wasted timber.

Formula

The core calculations are straightforward, but the units need care. All measurements are converted to millimetres for the picket count.

• Number of pickets = ceil( Fence length (mm) / (Picket width (mm) + Gap (mm)) )
• Number of posts = ceil( Fence length (m) / Post spacing (m) ) + 1
• Number of rails = ceil( Fence length (m) / Rail length (m) ) × Number of rails per bay

Where:

• Fence length – total length of the fence line in metres (m).
• Picket width – width of one picket in millimetres (mm).
• Gap – the space between adjacent pickets in millimetres (mm).
• Post spacing – centre-to-centre distance between posts in metres (m).
• Rail length – typically 3.0 m in the UK for treated timber rails.
• Rails per bay – usually 2 for a 1.2 m high fence, 3 for a 1.8 m high fence.

The ceil() function rounds any fraction up to the next whole number, because you cannot buy a fraction of a picket or post.

Worked Example

Using the default values from the calculator: fence length = 10 m, picket width = 100 mm, gap = 50 mm, post spacing = 1.8 m, price per picket = £2.50, price per post = £8.00, price per 3 m rail = £5.00.

1. Pickets: 10 m = 10,000 mm. Each bay (picket + gap) = 100 + 50 = 150 mm. 10,000 / 150 = 66.67, rounded up to 67 pickets.
2. Posts: 10 / 1.8 = 5.56, rounded up to 6, plus 1 = 7 posts.
3. Rails: 10 / 3 = 3.33, rounded up to 4 lengths per rail level. With 2 rail levels (standard for a 1.2 m fence), that’s 4 × 2 = 8 rails.
4. Cost: 67 × £2.50 = £167.50; 7 × £8.00 = £56.00; 8 × £5.00 = £40.00. Total = £167.50 + £56.00 + £40.00 = £263.50.

The calculator shows the same result: 67 pickets, 7 posts, 8 rails, and £263.50.

How to Choose Your Picket Size and Spacing

The classic UK picket fence uses 100 mm wide pickets with a 50 mm gap, giving a 2:1 ratio of wood to air. That’s a good starting point, but you can adjust for privacy or style.

• Privacy: Reduce the gap to 25 mm or even butt the pickets together (gap = 0). This uses roughly twice the timber and costs more.
• Openness: Increase the gap to 75 mm or 100 mm for a lighter look. This cuts material cost but reduces privacy and may not contain small pets.
• Picket width: 75 mm and 120 mm are also common. Wider pickets look more modern; narrower ones look more traditional.
• Height: Standard UK heights are 0.9 m, 1.2 m, and 1.8 m. The height affects the number of rails (2 for 1.2 m and below, 3 for 1.8 m) and the post size (75×75 mm for up to 1.2 m, 100×100 mm for 1.8 m).

Always measure the actual picket width before ordering – “100 mm” can be 95 mm or 105 mm depending on the sawmill. Use the actual width in the calculator to avoid ending up short.

Common Mistakes and How to Avoid Them

Even with a calculator, people make errors that cost time and money.

• Mixing units: The calculator uses millimetres for pickets and metres for length. If you enter the fence length in millimetres by mistake, the picket count will be 1000× too high.
• Forgetting the end post: A straight run of 10 m with posts every 1.8 m needs 7 posts, not 6. The +1 in the formula accounts for the post at the end of the run.
• Ignoring corners and gates: Every corner needs a post, and a gate needs extra posts on either side. If your fence has a corner, add one post for each corner. For a gate, add two posts (one each side) regardless of the post spacing.
• Rounding down: Always round up the number of pickets. If you round down, you’ll run out halfway through the last bay.
• Not accounting for waste: Add 5-10% extra for cutting, splitting, or damaged pieces. This is especially important with pickets, which are often sold in bundles and may have defects.

Cost Factors in the UK

Material prices vary widely by region and timber type. The calculator uses your input prices, so you can update them with current local quotes.

• Timber type: Pressure-treated softwood (spruce or pine) is the standard and cheapest. Hardwood (oak or cedar) can cost 3-5 times more but lasts longer.
• Post size: 75×75 mm posts are cheaper than 100×100 mm. For a 1.8 m fence, the larger post is recommended for stability.
• Concrete: Each post typically needs one 25 kg bag of post mix concrete (about £3-4). This is not included in the calculator – add it separately.
• Fixings: Galvanised nails or screws for pickets and rails add a small amount (about £5-10 per 10 m).
• Delivery: Timber yards often charge £30-50 for delivery, but some offer free delivery on orders over a certain amount.

As a rough guide, a 10 m, 1.2 m high picket fence in treated softwood with 100 mm pickets and 50 mm gaps costs about £250-£350 in materials (including concrete and fixings) as of 2024. Labour, if you pay a professional, would add another £200-£400.

Alternatives to Traditional Picket Fences

If the classic picket style isn’t right, consider these alternatives that use similar calculations:

• Closeboard fencing: Vertical feather-edge boards with no gaps – more privacy, but uses more timber and a different calculation (boards are lapped, so width is measured differently).
• Palisade (vertical bar) fencing: Metal or composite pickets that never rot. The spacing calculation is the same, but prices are higher.
• Hit and miss fencing: Horizontal rails with alternating gaps – a modern take that uses less timber.
• Composite pickets: Made from recycled plastic and wood fibre. They cost more upfront but need no painting and last 25+ years.

For any of these, the same basic formula for number of vertical members applies – just change the width and gap to match the product you choose.

Frequently Asked Questions

How many pickets do I need for a 30-metre fence?

With 100 mm pickets and 50 mm gaps, each bay is 150 mm. 30,000 mm / 150 mm = 200 pickets exactly. Add 5% for waste, so order about 210. If you use a 75 mm gap, the bay is 175 mm, and you’d need 172 pickets (round up from 171.4).

What is the standard gap between pickets?

In the UK, the most common gap is 50 mm for a 100 mm wide picket. This gives a balanced look and meets most planning requirements for front gardens (where fences over 1 m may need permission). Some people use 25 mm for more privacy, or 75 mm for a more open feel.

Do I need planning permission for a picket fence?

In England and Wales, you generally do not need planning permission for a fence under 1 m high at the front of your property, or under 2 m high at the back or side. However, if your property is a listed building or in a conservation area, you may need permission. Always check with your local council before building.

How deep should fence posts be set?

A common rule is to set posts at least one-third of their above-ground height into the ground. For a 1.2 m fence, that means a 1.8 m post buried 0.6 m. For a 1.8 m fence, use a 2.4 m post buried 0.6-0.75 m. Use post mix concrete and ensure the post is level and braced while the concrete sets.

How long will a treated pine picket fence last?

Pressure-treated softwood pickets typically last 10-15 years, with posts lasting longer if they are set in concrete. The pickets are the first to rot at the bottom where they meet damp ground. Keeping the fence clear of soil and vegetation can extend its life. Hardwood (oak) can last 25-40 years.

Can I use the calculator for a fence with a gate?

Yes, but you need to adjust the inputs. Measure the fence length as the total run minus the gate width. Add two extra posts for the gate (one on each side) to the posts output. For example, a 10 m run with a 1 m gate: enter 9 m as the fence length, then add 2 to the posts result.

Related

• Statistical t test calculator: formula, steps & examples
• Schofield Equation Activity Factor Guide
• Solve for b Calculator: Step-by-Step Algebra

in length | Fence length | m | 10 | 0
in picket_w | Picket width | mm | 100 | 0
in gap | Gap between pickets | mm | 50 | 0
in post_sp | Post spacing | m | 1.8 | 0
in price_picket | Price per picket | £ | 2.50 | 0
in price_post | Price per post | £ | 8.00 | 0
in price_rail | Price per rail (3m) | £ | 5.00 | 0
out pickets | Number of pickets | - | ceil(length * 1000 / (picket_w + gap)) | 0
out posts | Number of posts | - | ceil(length / post_sp) + 1 | 0
out rails | Number of rails (3m) | - | ceil(length / 3) * 2 | 0
out total_cost | Total material cost | £ | pickets * price_picket + posts * price_post + rails * price_rail | 2