How deep should fence post holes be?

Last checked 01-11-2026. A plain guide, not legal advice: check the official guidance below for your job.

A common rule of thumb is a hole about 600 mm deep for a fence up to about 1.8 m high, and about three times as wide as the post. Some makers say at least a third of the fence height. Go deeper for taller fences and exposed sites, and add the depth to the height above ground to get the post length. These are maker and merchant guidance, not regulations.

Work it out with the free fence panel and post calculator

The rules of thumb

There is no law or building regulation that sets fence post depth for a garden fence. What you have is guidance from fence makers and merchants. Here is what two of them say, so you can check the sums yourself:

• Depth: Jacksons Fencing gives 600 mm as its standard post hole depth, and lists 600 mm for every height in its table, up to 2.14 m. It says depth depends on ground conditions and the height of the fence.
• A third of the height: AVS Fencing says that, as a rough guide, the hole should be at least a third of the height of the fence, so a 6 ft fence needs an 8 ft post in a 2 ft deep hole.
• Width: both say about three times the width of the post. For a 100 mm post that is a 300 mm hole. Jacksons' own example is a 3 inch post in a 230 mm (9 inch) hole.
• Drainage under timber posts: Jacksons says timber posts must sit on at least 2 inches (50 mm) of ballast or gravel, not in concrete, so water can drain away from the end of the post.

Where the two rules give different answers, use the deeper one. For a 1.95 m fence, a third of the height is 1.95 / 3 = 0.65 m, which is deeper than 600 mm.

Work out the post length, with gravel boards

Post length = height above ground + depth in the ground. The height above ground is the panel plus the gravel board plus any trellis on top.

• A 1.8 m panel on a 150 mm gravel board stands 1.8 + 0.15 = 1.95 m above ground.
• With 600 mm in the ground the post is 1.95 + 0.6 = 2.55 m, so you would buy the next length up.
• Jacksons' table, which lists panel and gravel board heights together, gives a 2.4 m post for heights listed as 1.65 m/1.79 m and a 2.7 m post for 2.00 m/2.14 m, both 600 mm in the ground. Above 2.14 m it says to use its heavy duty posts.

Check the sizes of the panels and gravel boards you are actually buying, because they vary between makers.

Check the height against planning rules too. In England, the Planning Portal says you do not need planning permission for a fence up to 2 m high measured from ground level, or 1 m where it is next to a highway used by vehicles or the footpath of one. That is subject to conditions: not within the grounds of a listed building or on a boundary with one, and the right not removed by an Article 4 direction or a planning condition. Height is measured from ground level, so the gravel board and any trellis count towards it. The Planning Portal covers England and says Wales may differ; Scotland and Northern Ireland have separate planning systems, so check with the council.

Timber posts

• Dig the hole to the depth plus 50 mm, and put at least 50 mm of gravel in the bottom (Jacksons).
• Stand the post on the gravel, plumb it both ways and brace it.
• Fill round it with concrete or post mix. Jacksons' instructions show the post sitting on gravel with concrete round the sides, and mark a post bedded in a concrete base, with no gravel under it, as not recommended because water cannot drain and the post may rot early.
• Finish the top so it sheds water. Jacksons says to angle the post mix slightly, or mound soil at the top and slope it away from the post.

For a taller or heavier fence, or an exposed site, Jacksons recommends a heavier post (its heavy duty posts are 120 x 124 mm and start at 2.7 m long). See the section on wind below.

Concrete posts

Concrete posts use the same hole rules. AVS Fencing says to allow for the height of the panel and the gravel board, dig at least a third of the fence height and three times the post width, and suggests 1.5 bags of post mix a hole. Its other tips:

• Set the post deeper rather than cutting it. AVS says cutting a concrete post is hard work and throws out harmful dust. Cutting concrete produces silica dust, so plan the job to avoid it.
• Leave the concrete slightly proud of the ground so rainwater does not sit at the base of the post.
• Lay the gravel board on the ground to line up the next hole, and use a builder's line and pegs to keep the run straight.
• Concrete gravel boards slide into slotted posts from the top and can be bedded into the concrete at the base of the posts.

Concrete posts are heavy. Jacksons says they can weigh over 40 kg, often needing more than one person to lift them safely, so plan the lifting in your manual handling assessment.

Postcrete or mixed concrete

Blue Circle Postcrete is a ready-to-use mix of sand, cement and additives for fixing timber, concrete and metal posts. Its product data sheet (Tarmac, dated April 2014, still hosted by Wickes) gives this method:

• Dig the hole to the right depth and width for the post size.
• Fill the hole with water to a third of its depth.
• Pour the Postcrete evenly round the post until no standing water shows, then sprinkle water on top.
• Position and level the post. The sheet says it sets in 5 to 10 minutes.
• When set, cover the top with soil or grass. Do not mix it with water first, by hand or in a mixer.

Its table of 20 kg bags for a 10 cm (about 4 inch) square post:

• 15 cm wide x 60 cm deep: 1/3 bag
• 20 cm x 60 cm: 3/4 bag
• 25 cm x 60 cm: 1 3/4 bags
• 30 cm x 60 cm: 2 3/4 bags
• 20 cm x 75 cm: 1 bag
• 25 cm x 75 cm: 2 bags
• 30 cm x 75 cm: 3 1/2 bags

The sheet also sets limits. It is for domestic posts, decking posts, rotary washing lines and small to medium gateposts for gates less than 1.0 m wide. It must not be used where a specified compressive strength is needed, or for general concreting. For a wider gate, or where a design calls for a set strength, use concrete to the gate maker's or the designer's specification. Postcrete contains cement, so it needs the same skin and eye precautions as any cement product. Check the bag for the current figures, because the data sheet is not new.

Wind and exposed sites

No guidance we found gives a set extra depth for wind, so this is a judgement for the site. What Jacksons Fencing says about exposure:

• Taller, solid panels have more surface area, so wind puts more force on each post.
• Heavy duty posts suit exposed places such as coastal areas, open countryside and elevated gardens, solid panels over 1.52 m (5 ft), fences over 2.0 m, and sloping or stepped fences.
• A deeper post gives more resistance to the wind pushing it over, which matters more as the fence gets taller.
• For lower panels or sheltered gardens a standard post is often enough.

In practice that means on an exposed site you go deeper than 600 mm, use a heavier post, or both, and check that the fence height still suits the site.

Before you dig: buried services

A 600 mm post hole goes deeper than many services. HSE's guide HSG47 says most underground electricity cables are laid between 450 mm and 1 m deep, and gas service pipes on private property may have only about 375 mm of cover. It also says never to assume depths, because services may be shallower than that.

• Get plans of the buried services and look at them before you dig. HSE says plans only show the likely position.
• Scan the line of the fence with a cable locator, used by someone trained in it, and keep using it as you dig.
• Look for signs of services: HSG47 lists lamp posts, gas service pipes going into buildings, pit covers, marker posts and old reinstated trenches. No signs does not mean no services.
• Dig carefully by hand where services may be. HSE recommends digging alongside a service rather than straight down on top of it, and insulated tools near cables.
• Mark the line of a service with wooden pegs to one side of it. HSG47 says steel pins, spikes or long pegs that could damage shallow services should not be used.

The guide on underground services covers this in more detail.

Worked example: a garden fence in Grasmere

A cottage garden in Grasmere, in a sheltered spot, gets a new 19.4 m run of fencing along the back boundary. It is not next to a road. The builder plans 1.8 m high panels 1.83 m wide on 150 mm gravel boards, with 100 mm square timber posts.

• Panels: 10. Posts: 10 + 1 = 11. Check: 10 x 1.83 + 11 x 0.1 = 18.3 + 1.1 = 19.4 m.
• Height above ground: 1.8 + 0.15 = 1.95 m. That is under 2 m, so it is within the Planning Portal limit, as long as the ground does not drop along the run and no other condition applies.
• Depth: Jacksons' standard is 600 mm; a third of the height is 1.95 / 3 = 0.65 m. The builder takes the deeper figure and rounds it to the post lengths on sale: 2.7 m posts give 2.7 - 1.95 = 0.75 m in the ground.
• Hole: three times the post width is 3 x 100 = 300 mm wide. Dig 750 + 50 = 800 mm deep, to allow for 50 mm of gravel under each post.
• Gravel: 0.3 x 0.3 x 0.05 = 0.0045 m3 a hole, so 11 x 0.0045 = about 0.05 m3 in all.
• Postcrete: the data sheet gives 3 1/2 bags for a 10 cm post in a 30 cm x 75 cm hole, so 11 x 3.5 = 38.5, call it 39 bags. The gravel sits below the 750 mm the table allows for, so the figure applies as it stands. A 25 cm hole would need 2 bags each, 22 in all, but would be narrower than the three-times rule.

39 bags at 20 kg is 780 kg, so check the van's payload and plan the handling. If the same fence went on the open fellside above the village, the builder would go for heavy duty posts, set deeper, as Jacksons advises for exposed sites, and work out the post mix again for the bigger holes using the bag maker's figures.

Sources

• Jacksons Fencing: How deep to dig post holes
• Jacksons Fencing: Key instructions for timber fence post erection (PDF)
• Jacksons Fencing: When to use heavy duty fence posts
• AVS Fencing: Installing concrete fence posts and gravel boards
• Tarmac: Blue Circle Postcrete product data sheet (hosted by Wickes)
• Planning Portal: Fences, gates and garden walls, planning permission
• HSE: Electricity, underground cables
• HSE: Avoiding danger from underground services (HSG47)