Retaining Wall Block Calculator Australia — Besser Blocks & Cost
Building a retaining wall? This free retaining wall block calculator helps Australian DIYers and builders work out exactly how many blocks, cap blocks, base gravel, backfill gravel, and landscape fabric a wall needs — plus a full cost estimate — in metres and Australian dollars. It's sized to block dimensions similar to besser-style blocks stocked by Bunnings. And unlike most block calculators, we don't stop at the blocks: drainage backfill is built into the number too, since poor drainage is the single biggest cause of wall failure.
How to use this calculator
1. Measure your wall
Measure your wall's total length and height in metres. Height should run from the bottom of the buried base course — most walls bury their first course below ground for stability — to the top of the finished cap, not just the visible face. Only measuring what you can see above ground is a common way to under-order blocks. For curved or terraced walls, measure each straight run separately and add the lengths together; the calculator handles the extra cutting waste as a percentage, not as separate geometry.
2. Choose a block size and shape
Pick a block size — 300×100×200mm or 400×150×300mm, both common besser-style dimensions — then set your wall shape: straight, curved, or terraced. This drives the waste allowance in your block count: straight walls carry 5%, curved 10%, and terraced (stepped) walls 15%, since each step adds more cut edges.
3. Set your gravel depth and backfill option
Base gravel depth defaults to 150mm, a standard compacted-base thickness for a garden wall — go deeper for a taller wall. Leave backfill gravel switched on unless your soil genuinely free-drains: this is the drainage zone directly behind the wall, and skipping it is the most common cause of wall failure across Australia, especially after a heavy wet-season downpour.
4. Review your blocks, gravel, and cost breakdown
Results update live. You'll see total blocks (waste already included), cap blocks if toggled on, base and backfill gravel in tonnes, landscape fabric area, and a full cost breakdown by line item, in metres and Australian dollars — everything you need before a Bunnings run.
The formula we use
Here's the exact math. Wall face area is length × height. Blocks per row is wall length divided by block length, rounded up; rows needed is wall height divided by block height, rounded up. Multiply those together, then apply your shape's waste factor — straight ×1.05, curved ×1.10, terraced ×1.15 — and round up to a whole block.
Cap blocks, if switched on, add one finishing block per block-length along the wall. This capping row sits on top of the waste-adjusted total, not folded into it — an uncapped besser wall is exposed to water intrusion at the top edge that erodes the blockwork over time.
Gravel is where a lot of calculators get vague. Our base trench runs two block-depths wide, filled to your chosen depth, converted to tonnes at 1.6 tonnes per cubic metre, a standard density for compacted gravel. Backfill gravel, the drainage wedge behind the wall, assumes a 0.3m wide zone running half the wall's height. Landscape fabric covers the trench width plus the wall face, doubled for both sides of the gravel zone.
A worked example
Let's walk through a real 5m × 1.2m wall — big enough to need a permit check in most states, which we'll get to below — using 300×100×200mm besser-style blocks, straight, economy tier, with cap blocks and backfill gravel both on.
Blocks per row: 5m ÷ 0.3m (block length) = 17, rounded up. Rows needed: 1.2m ÷ 0.1m (block height) = 12 rows. That's 204 blocks before waste; straight walls carry a 5% allowance, so 204 × 1.05 = 214.2, rounded up to 215 blocks.
Cap blocks: 17 (one per block-length along the wall). Base gravel: a trench roughly 0.4m wide by 150mm deep along the 5m run works out to about 0.48 tonnes. Backfill gravel, the drainage zone behind the wall: about 1.44 tonnes. Landscape fabric: about 16 sqm.
At Bunnings' economy tier (A$8.15 a block, Eziwall-style), 215 blocks cost A$1,752.25. Cap blocks at A$8.42 each add A$143.14. Gravel — base plus backfill, at A$128 a tonne, noticeably higher here than in the UK or US — adds about A$246, and fabric at A$2.45 a square metre adds roughly A$39. All in: around A$2,180 for a wall this size, genuinely worth a council check first given the height.
Regional cost context
Australian retaining wall prices sit noticeably above UK or US equivalents once converted to a common unit — gravel especially, which runs more than double the US per-tonne price.
Estimates are indicative only. As an Amazon Associate we earn from qualifying purchases. Retaining walls over 1 m and decks above certain thresholds may require council approval and/or an engineer (Form 15/16 in QLD). Verify with your local council before starting work.
| Item | Price | Unit |
|---|---|---|
| Economy concrete block | A$8.15 | block |
| Premium concrete block | A$13.25 | block |
| Natural stone block | A$37 | block |
| Cap block | A$8.42 | block |
| Base / backfill gravel | A$128 | tonne |
| Landscape fabric | A$2.45 | sqm |
Prices from Bunnings, current as of our last check — see our Methodology page for sources and verification dates.
Bunnings' Eziwall-style economy block is the standard pick for most garden retaining walls — inexpensive relative to the premium tier, though still pricier than equivalent UK or US product. Adbri Versawall-style premium block steps up finish quality at around 1.6x the economy price, and is also what we've used for cap block pricing, since no economy-specific cap price was available. Natural stone runs over 4x economy, the widest tier spread of any region we cover, and is usually reserved for visible, front-of-house walls.
Gravel at A$128 a tonne is the standout figure here: more than double the US equivalent, and a genuine cost driver on any wall with meaningful backfill volume. All figures reflect our last direct Bunnings check (see our Methodology page for sources and dates); expect variation between stores and states.
Do you need a permit or approval?
Retaining wall approval rules in Australia are set state by state, so treat any single number here as a starting point.
A commonly cited trigger is 1 metre of exposed wall height — Victoria's Building Regulations 2018, for example, generally require a permit above that height. Below it, many walls are exempt from council approval, though local planning schemes can still add their own conditions, like setbacks or drainage requirements, even under the height trigger. Queensland goes further for any engineered wall: it requires a Registered Professional Engineer of Queensland (RPEQ) to certify the design via Form 15, or Form 16 for inspection, regardless of the exemption height, once a wall is doing real structural work.
Quick heads-up: a wall over about 1m holding back a driveway, pool, or sloped block is exactly the case where council approval and an engineer are both worth the cost, wherever you are. Confirm current thresholds with your specific council before digging — this calculator estimates materials, not compliance.
Common mistakes to avoid
- Skipping backfill gravel to save money. Drainage, not the blocks themselves, is what actually holds most walls up — this shows up hardest after a heavy wet-season downpour.
- Forgetting the buried course. If your height measurement only covers what's visible above grade, you'll under-order for the buried first course that gives the wall its footing.
- Guessing at waste % instead of picking the right shape. Straight, curved, and terraced carry genuinely different allowances — 5%, 10%, and 15% — so picking "straight" for a stepped terrace wall leaves you short.
- Building over 1m without a council check. Some councils add conditions even under the exemption height — a quick call beats a stop-work order.
- Skipping cap blocks to save a few dollars. An uncapped top row is exposed to water intrusion that erodes the blockwork from the top down.
- Assuming every Bunnings stocks the exact besser size you've planned around. Confirm dimensions in-store first — swapping block presets changes your row count, not just your total.
- Planning a deck above your retaining wall? Check our composite decking calculator. Painting the wall's exposed face? Use our paint coverage calculator.
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Frequently asked questions
How many besser blocks per square metre?
It works out to roughly 3-4 blocks per square metre for a standard 300×100×200mm besser-style block, depending on your exact wall height and row alignment — but this calculator doesn't use a flat area-rate shortcut, since block count depends on how your wall length and height divide into whole rows and columns. For a 5m × 1.2m wall, straight shape, that's 215 blocks total (including a 5% waste allowance), across 6 sqm of wall face. Use the calculator above for your exact count.
Do I need council approval for a retaining wall over 1 m?
In most states, yes — 1 metre of exposed height is a commonly cited trigger, and Victoria's Building Regulations 2018 generally require a permit above that height. Below it, many walls are exempt, though local planning schemes can still add their own conditions like setbacks or drainage requirements even under the height trigger. Rules are set state by state, so confirm the exact threshold with your specific council before digging — this calculator estimates materials, not compliance.
Do I need an engineer for my retaining wall?
In Queensland, yes, for any engineered wall — a Registered Professional Engineer of Queensland (RPEQ) must certify the design via Form 15, or Form 16 for inspection, regardless of the exemption height, once a wall is doing real structural work. Other states don't universally require RPEQ certification, but a wall over about 1m holding back a driveway, pool, or sloped block is exactly the case where an engineer is worth the cost wherever you are. Check your council's current requirements.
How much gravel and drainage do I need behind the wall?
For a 5m × 1.2m wall, budget roughly 0.48 tonnes of base gravel under the wall plus about 1.44 tonnes of backfill gravel behind it — just under 2 tonnes combined, plus about 16 sqm of landscape fabric to stop soil clogging the gravel. Backfill assumes a 0.3m wide drainage zone running half the wall's height. Skipping it is the most common cause of wall failure in Australia, especially after a heavy wet-season downpour.
How much does a retaining wall cost per m² in Australia?
For a 5m × 1.2m wall (6 sqm of wall face) using Bunnings' economy Eziwall-style block, expect around A$2,180 all-in — roughly A$363 per square metre. That breaks down to A$1,752 for 215 blocks, A$143 for cap blocks, about A$246 for base and backfill gravel (gravel runs over double the US price here), and roughly A$39 for landscape fabric. Premium block runs about 1.6x economy. Use the calculator above for your exact dimensions and cost.
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Estimates are indicative only. As an Amazon Associate we earn from qualifying purchases. Retaining walls over 1 m and decks above certain thresholds may require council approval and/or an engineer (Form 15/16 in QLD). Verify with your local council before starting work.
Last updated: August 2026. Estimates are for planning purposes only. Verify with local suppliers before purchase, and check local codes and permit requirements before starting work. Block dimensions shown are generic engineering approximations; actual product dimensions vary by brand — verify with your supplier before ordering.