What this calculator does
It turns two measurements into a materials list. Enter the length of the wall, the finished height, the sleeper you want and whether a fence is going on top, and it returns quantities for a straight post and panel wall: sleepers, end and intermediate posts, bags of concrete for the pier holes, agi pipe, geo fabric, drainage aggregate, wedges, and post caps where they apply. Every line shows the arithmetic behind it, so you can check the numbers rather than take them on trust.
The spacings come from our own installation guides, and every product it names is something we stock and can deliver. It is an estimate, not a quote, and it is not an engineered design.
How to use it
- Measure the wall face, not the boundary. Length is measured along the line the wall follows. Height is the exposed height of the finished wall, not counting the pier depth below ground.
- Choose the sleeper before you read the post count. Sleeper length sets the post centres, so moving from a 2380mm sleeper to a 1980mm sleeper changes the number of posts as well as the number of sleepers.
- Answer the fence question honestly. A fence on top widens the post centres by 10mm and adds a bracket at every post. It also adds load, including wind load, which belongs in the wall design rather than being bolted on afterwards.
- Read the set out and pier details under the table. That is where the post centres, the length of the last bay, the pier size, the post length and the lean back are spelled out.
- Send the list to us when you are done. The button under the results carries the whole take off into a quote request, so nobody has to retype it. Nothing you enter leaves your browser until you press it.
What the calculator assumes
These are the rules it applies. They are the same rules our own installation guides use, and they are deliberately conservative on pier depth.
| Assumption | The rule it uses |
|---|---|
| Wall shape | One straight run of even height, with nothing behind it but soil |
| Post centres | Sleeper length plus 20mm, or plus 30mm when a fence sits on top |
| Post count | Bays plus one, with a C post at each end and H posts in between |
| Courses | Wall height divided by the 200mm sleeper height, rounded up |
| Pier depth | Equal to the wall height, so the post ordered is twice the wall height |
| Pier hole | 450mm diameter, concreted, 25MPa minimum recommended |
| Concrete yield | About 10 litres of set concrete per 20kg bag. Check the yield printed on the bag you buy |
| Drainage zone | 300mm wide behind the wall, for the full height and the full length |
| Agi pipe | One run the full length of the wall, 65mm up to 1m high and 100mm at 1m and above |
| Geo fabric | The full length of the wall, wrapped down the back and up the cut out behind it |
| Wedges | About two per sleeper, to chock each one forward against the post flange |
| Post caps | One per post on concrete and timber walls, matched to the C or H profile |
| Lean back | At least 50mm per metre of height, so the wall is not plumb by design |
| Post range | Standard galvanised posts to 3.8m, then the heavy duty 150UC23 and 150PFC range to 6.0m |
A worked example
A 10 metre wall, 1 metre high, in 2380mm concrete sleepers with no fence on top comes out at 2400mm post centres, 5 bays and 6 posts, 5 courses and 25 sleepers. The posts are 2.0m, set in six 450mm pier holes 1 metre deep, which is 96 bags of concrete. Behind it goes 10 metres of agi pipe, 10 metres of geo fabric and 3m3 of drainage aggregate, with about 50 wedges, 2 C caps and 4 H caps. Change the sleeper to 1980mm and the same wall needs 6 bays and 7 posts instead.
What the calculator cannot know
This is the honest part. A take off from two numbers is a starting point, and these are the things that move it.
- Corners and returns. A change in direction needs a corner post and it changes the bay lengths on both sides of the corner. The calculator prices one straight run.
- Steps. Walls that step up a slope, and footings that step with them, change the post length and the course count bay by bay.
- Cut sleepers. The last bay is almost never a full bay, so a sleeper gets cut for every course at that end. The calculator counts whole sleepers and tells you how long the last bay is, but it does not price the cutting or the offcuts.
- Waste and breakage. There is no waste allowance in any of the numbers. Add your own on the consumables.
- The ground. Soil type, fill, rock, groundwater, a sloping site and how much of the pier is in good material are all site conditions the calculator has no way of seeing.
- Surcharge behind the wall. A driveway, slab, shed, pool or another wall stepping above the zone of influence changes the loads on the wall and the design that carries them.
- Site specific engineering. Where a wall has an engineered design, that design governs the post section, the spacing, the embedment and the pier. Use its numbers, not ours.
- Whether you need approval. That depends on your height, what sits behind the wall and your own council.
- Delivery. Freight depends on the size of the load, your address and the access at your site, so it is quoted separately.
How to read the result
Treat the table as a shopping list to argue with, not a purchase order. Three things are worth doing before you order anything.
- Check the last bay length in the set out list. If it is well short of a full bay, it is often cheaper to shift the wall line or change sleeper length than to cut every course.
- Check the post length against the pier depth you can actually dig. If rock or services stop you at the depth the calculator assumed, the post length and the design both change.
- Check the post type at each position. Two C posts and the rest H posts is right for a single straight run, and wrong the moment there is a corner, a step or a wall that stops against a structure. Our guide to choosing steel posts works through it.
The lines tagged Estimate or Optional are the ones we expect to change. Wedges are sold in bags, and caps are a finishing item rather than a structural one.
Approvals and engineering
Walls over about 1 metre high commonly need council approval and an engineered design, and approval can also be triggered by loads behind the wall or by being close to a building or another wall. Thresholds and conditions vary by council across South East Queensland and Northern NSW. Confirm your own situation with your council or a licensed private building certifier before you order material.
In Queensland, professional engineering services must be carried out by a Registered Professional Engineer of Queensland or under their direct supervision. Our council approval guide sets out what we have been able to verify council by council, and the wall height guide sorts materials and requirements by height band. Neither is a substitute for asking your own council.
What to do next
- Get it priced. Send the list through with the button under the results, or request a quote with your wall length, height, whether a fence is going on top, your suburb and a couple of site photos. Our team confirms every line, the post type at each position and your delivery cost before anything is priced.
- Or order it yourself. Browse sleepers and blocks, posts and corners, fixings and caps and drainage and base. Cosmetic seconds and clearance stock suits courses that end up buried.
- Read before you dig. The steel post installation guide, the drainage guide and the cross section diagram show how the post, the sleepers, the drainage zone and the backfill sit together.
- Check how it gets there. Delivery and installation covers crane truck access, and the fire ant movement controls that apply to bulk gravel, sand and soil in South East Queensland.
28 Shettleston Street, Rocklea QLD 4106. Monday to Friday, 6am to 4:30pm. Phone (07) 3716 0191 or email enquiry@hybuilt.com.au.