How Many Fence Panels, Posts & Bags of Postmix Do I Need?

One of the most common questions when planning a fence is simple: how many panels, posts, and bags of postmix do I actually need? Getting it right first time saves wasted money, avoids mid-job delays, and ensures your fence is solid and long-lasting.

This guide walks through the calculation step by step, whether you’re a DIY customer replacing a garden fence or a trade customer pricing up a full run. You can source everything mentioned below from our Timber Fencing & Fence Panels range.

Step 1: Measure the total fence length

Start by measuring the full length of the fence line in metres. Always measure along the ground where the fence will be installed, not just between existing posts.

For example:

Total fence run: 18 metres

Step 2: How many fence panels do I need?

Most standard fence panels are 1.83m (6ft) wide. To calculate the number of panels:

Total fence length ÷ panel width = number of panels

Example:

18m ÷ 1.83m ≈ 9.8 panels

Always round up, so you would need 10 fence panels.

You can browse available sizes in Fence Panels.

Step 3: How many fence posts do I need?

The number of posts is usually:

Number of panels + 1

Using the example above:

10 panels = 11 fence posts

This allows for a post at both ends of the fence run.

Browse options in Fence Posts, including timber and concrete posts.

Corner fences and returns

If your fence changes direction or includes returns, allow extra posts for:

Corners
Ends against walls or buildings
Gates

It’s often safer to allow one spare post, especially on longer runs.

Step 4: How many bags of postmix do I need?

As a general rule:

1 bag of postmix per fence post for normal ground conditions
2 bags per post for soft or loose ground

Using the example:

11 posts = 11–22 bags of postmix depending on ground conditions

Postmix and fencing fixings can be found in Fixings & Postmix.

Step 5: Don’t forget gravel boards

Gravel boards protect the bottom of the fence from ground moisture and help extend the life of your panels.

As a rule:

1 gravel board per panel

For 10 panels, allow 10 gravel boards. Options are available in Gravel Boards.

Typical fencing materials checklist

For a straight 18m fence run using standard panels:

10 fence panels
11 fence posts
11–22 bags of postmix
10 gravel boards
Exterior fixings and brackets

Timber vs concrete posts: does it change the calculation?

The quantities stay the same whether you choose timber or concrete posts. The difference is longevity and maintenance.

You can mix and match using:

Delivery and local support

Fencing materials are bulky and heavy. Before ordering, check Delivery Information to make sure everything arrives together.

If you want help checking quantities or choosing the right products, use Contact Wern-Wood with your fence length and ground type, and we’ll point you in the right direction.