Fence calculator

How the calculator counts

Each run is worked out on its own and then added up. The last panel or bay of a run is usually shorter than the rest. The calculator lists these short panels so you can cut them and put them beside a corner or a gate post, which is where Stratco's installation guide suggests they go. Runs that meet at a corner share a post, so a fence made of two runs needs one post more than the number of panels or bays.

For the example in the quick answer, 15 m ÷ 2.35 m is 6.4, so 7 panels, and 30 m takes 13. That is 20 panels on 21 footings. One panel in each run is cut short, to 0.90 m and 1.80 m.

Steel sheet fences: panels, posts and footings

Colorbond fences are sold as panel kits. A standard Lysaght panel is 2.35 m wide with three infill sheets, or 3.1 m wide with four, and comes with two posts, a top rail and a bottom rail. Between panels, the two posts are screwed back to back and share one footing. Standard heights are 1.5, 1.8 and 2.1 m. Four-sheet panels stop at 1.8 m.

Every footing is 200 mm across. How deep it goes depends on how exposed the site is, the wind region and the soil. These are Lysaght's minimum depths for three-sheet panels 1.5–1.8 m high in wind region A, which covers most of Australia:

Four-sheet panels, 2.1 m fences and wind region B need deeper footings, and the calculator uses the guide's full table for them. Lysaght's own worked example, a four-sheet fence in a Sydney suburb on stiff clay, needs 400 mm. Some combinations aren't covered at all, and in open ground some fences also need a flat stiffener inside each post. The calculator tells you when either applies. Never set footings in loose fill that hasn't been compacted.

• Post length. Lysaght works it out as footing depth minus 40 mm, plus the fence height, plus a 50 mm gap under the bottom rail. You then buy the nearest stock length of 2.1, 2.4, 2.7 or 3.0 m that leaves 40–150 mm of concrete under the post, and cut it down if needed. A 1.8 m fence on 300 mm footings takes 2.1 m posts. On 500 mm footings it takes 2.4 m posts cut to length.
• Concrete. A 200 mm footing 300 mm deep holds about 9.4 litres, roughly one 20 kg bag. BlueScope's own installation guide is simpler and more conservative. It uses 400 mm in rock, 600 mm in clay and 900 mm in sand or loose fill, with one, two and three 20 kg bags per hole.
• Keep it clear of the ground. Keep at least 50 mm between the bottom rail and the ground. Don't bank soil or garden beds against the fence, and don't use it as a retaining wall. Soil against the steel holds moisture and rusts it, which BlueScope's guide warns about.
• Genuine steel. BlueScope says genuine Colorbond fencing is laser-engraved at least three times in each 2.4 m section. Its warranty needs the fence installed and maintained to the guidelines. Lysaght's guide also says pool water splashed on the fence voids the warranty.

Timber paling fences

Timber Queensland's data sheet on residential fences covers paling fences up to 1.8 m high. It sets these sizes:

• Posts. Set them about 450 mm deep for a fence up to 1.2 m and 600 mm for one up to 1.8 m. Holes need to be at least 300 mm across, with 100 mm of coarse gravel in the base so they drain. Fill the rest with concrete sloped to shed water, or with earth rammed down every 150 mm. For hardwood posts, Timber Queensland recommends no-fines concrete. For how soil and wind change the depth, see the fence post depth guide.
• Rails. Use two rails for a fence up to 1.2 m and three for one up to 1.8 m. Each rail is two bays long, with the joins in the top and bottom rails staggered. Fix each rail to each post with a cup-head bolt, a batten screw or two nails, all hot-dip galvanised or stainless steel.
• Palings. Common sizes are 100 × 15 mm and 75 × 15 mm. Use two nails per paling at each rail. Palings shrink, so butted palings open up small gaps over time. For full privacy, Timber Queensland lays them in two layers. The back layer is spaced 50 mm apart, and the front layer covers the gaps.
• Treatment. Posts and plinths need at least H4, because they are in the ground. Palings, rails and capping need H3.

Per metre of fence, 100 mm palings take 10 butted, about 8.3 with 20 mm gaps, and about 13.3 lapped in two layers. The quick-answer runs in 100 mm butted palings take 450 palings, 21 posts, 33 rails of 4.8 m and 2,700 nails. With the holes concreted, they also take about 82 bags. That much concrete is roughly three-quarters of a cubic metre, so compare the price with a small ready-mix load in the concrete calculator.

Gates and free ends

• Steel. Gate posts are square hollow section (SHS) steel. Stratco's guide makes the three holes nearest a free end, and gate post holes, 100 mm deeper than the rest. BlueScope suggests tapering the last two panels at a free end down to half height, which looks better and is stronger than a full-height end.
• Timber. Frame gates with the same rails as the fence plus a diagonal brace, set at 30–60°. Use three hinges on gates over 1.2 m, as Timber Queensland recommends.

Before you build

• Your neighbour. Timber Queensland's advice is to agree the type, height and sharing of costs with your neighbour before starting. Unless you agree otherwise, the centre of the posts goes on the boundary line.
• Council rules and covenants. These can limit where a fence goes, how high it is and how it is built. Check them first, as both guides say.
• Underground services. Find out where power, gas and water lines run before you dig. BlueScope's guide points you to the Dial Before You Dig service.
• Pools. A fence that forms part of a pool barrier has its own rules. For heights, gaps and gates, see pool fence rules in Australia and New Zealand.

Fence questions