How to Plan and Build a Garden Fence: Posts, Panels, and Materials

Measure the perimeter, not your patience

I have built more fences than I can count — privacy fences, picket fences, stockade fences, post-and-rail for a hobby farmer who kept losing goats. And the mistake I see most often from DIYers is the same one every time: they drive to the builder’s merchant with a vague idea of how long their boundary is, buy what looks like roughly the right amount of materials, and end up either short by three panels or drowning in leftover concrete. Neither is fun.

A fence is one of the most satisfying DIY projects you can take on. You start the morning looking at an open boundary and end the day with a proper structure. But getting the materials right before you start is everything. Running out of post-mix concrete on a Saturday afternoon when the merchant has closed is the kind of mistake that adds a week to a one-day project.

This guide walks you through calculating exactly what you need — posts, panels, concrete, and stain — so you order once, build once, and do not lose a weekend to undersupply.

Step 1: Calculate your fence materials

Before anything else, you need three measurements: the total length of fence you are building, the height you want, and the spacing between posts (which is usually determined by your panel width — standard panels are 1.83 metres or 6 feet wide).

Walk the perimeter with a tape measure. Include every straight run and note where you need gates. Gates require their own posts, and the opening width determines the gate panel size. If your boundary is not straight, break it into segments and measure each one.

A few things people forget: you need a post at every corner and every end point, not just at panel intervals. If you are running along a neighbour’s boundary, confirm the line before you dig — boundary disputes over a fence that is six inches on the wrong side are remarkably common and remarkably unpleasant.

Let’s use the Fence Calculator to work out your posts, panels, and materials.

Add 10% to your panel and rail quantities as a buffer. Panels can have defects, and cutting around obstacles (trees, uneven ground, utility boxes) sometimes means sacrificing part of a panel. Having a spare is cheaper than making another trip.

Step 2: Calculate concrete for your post holes

Every fence post needs to be set in the ground solidly enough to resist wind load, which means concrete. The amount of concrete per post depends on the hole diameter, hole depth, and the post size. Standard practice is a hole roughly three times the width of the post and at least one-third of the total post length deep. For a 2.4-metre (8-foot) post that will stand 1.8 metres above ground, you need about 600mm of the post in the ground.

This is where people most frequently under-order. A single post hole uses more concrete than you think — typically one to two bags of post-mix per hole, depending on the hole size. Multiply that by twenty or thirty posts and you are looking at a serious pile of concrete bags.

Use the Post Hole Concrete Calculator to get an accurate quantity.

Quick tip from years on job sites: fast-setting post-mix concrete is your friend for fence work. You pour it dry into the hole around the post, add water, and it sets in about 20 to 30 minutes. No mixing required. It lets you set posts and hang panels on the same day, which keeps the project moving.

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Step 3: Work out your stain or treatment needs

A new timber fence looks great for about six months before the weather starts turning it grey. Staining or treating the wood protects it from moisture, UV damage, and rot, and can double the lifespan of the fence. The time to stain is as soon as the wood is dry enough to absorb the product — usually two to four weeks after installation for fresh timber.

The amount of stain you need depends on the total surface area of the fence (both sides if you want full coverage, though most people only do the visible side) and the coverage rate of your chosen product, which is printed on the tin.

Use the Fence Stain Calculator to estimate how much stain or preservative to buy.

Rough-sawn timber absorbs significantly more stain than planed timber — sometimes twice as much per square metre. If your panels are rough-sawn (which most fencing panels are), use the higher end of the coverage range on the product label. Under-ordering stain mid-project means you might not get an exact colour match from a different batch, which can leave visible variation.

Building tips from too many fences

Once your materials are on site, here are the lessons that come from doing this work day in, day out:

Set your end and corner posts first. String a line between them at the top to give you a straight reference for all the intermediate posts. A fence that wanders even slightly is visible from a distance, and once the concrete is set, you are not moving those posts.

Check every post with a spirit level. Plumb in both directions before the concrete sets. A post that is 10mm out of plumb at the base will be 30mm or more out at the top, and every panel it connects to will show the error.

Leave a gap at the bottom. Unless you are building specifically for animal containment, leave 25 to 50mm between the bottom of the panels and the ground. This prevents moisture wicking up into the panel timber and extends the life of the fence considerably. It also makes mowing along the fence line much easier.

Use galvanised or stainless fixings. Standard steel screws and brackets will rust within a year in outdoor conditions, leaving orange stain streaks down your freshly treated fence. Spend the extra on galvanised or stainless hardware. It is a small cost relative to the project and saves you from having to replace fixings in two years.

Order everything at once. Delivery charges from a builder’s merchant are the same whether you order ten panels or thirty. One delivery with everything on it costs less and wastes less of your time than three separate trips for things you forgot.

A well-planned fence goes up quickly, looks sharp, and lasts a decade or more with basic maintenance. The key is in the preparation — get your numbers right, order what you need, and spend your energy building rather than scrambling for materials.

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