How many sleepers do I need for a retaining wall?

Bays × courses. Each bay is one sleeper length plus a small gap; each course is 200 mm high. An 8 m wall 0.8 m high in 2 m sleepers is 4 bays × 4 courses = 16 sleepers.

How deep do retaining wall posts go?

At least 1 m for walls up to 1 m high, then the next 0.2 m step at or above the wall height (a 1.3 m wall gets 1.4 m), in 450 mm holes with 100 mm of concrete under the post. Your sleeper maker's table or engineer sets the final depth.

Do I need approval for a retaining wall?

Often, above a low height: 500 mm in parts of WA, 600 mm in NSW, and 1 m in QLD and VIC, with conditions on distance from boundaries and buildings. Check with your council.

What drainage does a sleeper wall need?

About 300 mm of 20 mm gravel behind the wall to 200 mm below the top, a slotted ag pipe along the base falling 1 in 100, filter fabric between soil and gravel, and a soil plug on top.

Free calculator

Retaining wall calculator

Bays = wall length ÷ (sleeper length + gap). Courses = height ÷ 0.2 m. Sleepers = bays × courses; posts = bays + 1. Posts go into the ground at least 1 m, deeper for taller walls (the guide steps up with the height), in 450 mm holes of concrete.

Your job

Wall

Length

Retained height

Sleepers and posts

Post embedment

Hole diameter

Embedment defaults to the guide's table: 1.0 m up to a 1.0 m wall, then the next 0.2 m step at or above the wall height (1.2, 1.4, 1.6 m), and the deeper listed value above 1.6 m, with 100 mm of concrete under the post. Stock post lengths are 0.9 to 3.6 m; anything longer, or walls over 1.8 m, needs heavier posts your engineer specifies.

At 0.80 m this is over the no-approval limit in WA, NSW. Check with your council before you build.

Optional

Your price per sleeper

Ask your supplier. The greyed number is an example only and is never used in your result.

Sleepers stacked between steel posts, with the posts set in concrete below ground. Right: the drainage behind the wall.

Sleepers

16sleepers

4 bays × 4 courses of Concrete 2000 × 200

Posts

3 joiner, 2 end; 1.8 m long

Concrete

0.87m³

97 × 20 kg bags for 5 holes 450 mm wide × 1.10 m

Drainage gravel

1.44m³

300 mm wide behind the wall, plus 8.0 m of ag pipe

Filter fabric

8.8m²

Between the soil and the gravel

The working, with your numbers

1. Bays8.00 ÷ 2.030 ↑= 4
2. Courses0.80 ÷ 0.2, rounded up= 4
3. Postsbays + 1 run end= 5
4. Concrete5 × π × 0.225² × 1.10= 0.875 m³
5. Gravel8.00 × 0.3 × (0.80 − 0.2)= 1.44 m³

Typed those measurements in by hand?MetreMate measures them straight off your PDF plans. Free to start.

The formula, in plain words

1Bays per run = run length ÷ (sleeper length + the maker's gap), rounded up. Courses = height ÷ 200 mm, rounded up.
2Sleepers = bays × courses. Posts = bays + 1 per run, less one for each shared corner post.
3Post length = wall height + embedment (1.0 m up to a 1.0 m wall, then the guide's next step at or above the wall height), with 100 mm of concrete below. Stock posts run 0.9 to 3.6 m.
4Concrete = posts × π × (hole diameter ÷ 2)² × hole depth, in 20 kg bags at 110 a cubic metre.
5Drainage: 300 mm of 20 mm gravel behind the wall to 200 mm below the top, slotted ag pipe the full length, and filter fabric.

Worked example

An 8 m long, 0.8 m high wall in 2000 × 200 mm concrete sleepers, posts 1.0 m in the ground in 450 mm holes.

1.Bays: 8 ÷ 2.03 = 3.9, so 4. Courses: 0.8 ÷ 0.2 = 4. Sleepers: 16.
2.Posts: 4 + 1 = 5 (3 joiners and 2 ends), each 0.8 + 1.0 = 1.8 m.
3.Concrete: 5 × π × 0.225² × 1.1 = 0.87 m³, about 97 bags.
4.Drainage: 8 × 0.3 × 0.6 = 1.44 m³ of gravel and 8 m of ag pipe.

Answer: 16 sleepers, 5 posts of 1.8 m, 0.87 m³ of concrete and 1.44 m³ of gravel.

How to measure it

Measure each straight run of wall and how many corners join them.
Measure the height of soil the wall will hold back.
Check the sleeper size and the post spacing your sleeper maker gives.
Check your council's height limit before you build; over 1 m, get an engineer.

Where the numbers come from

Every default in the calculator is a number a supplier or manufacturer publishes. We list the source next to it so you can check.

What	Value	Source
Concrete sleepers are 200 mm high: 2.5 per m² of wall for 2 m sleepers	200 mm	Austral Masonry, Explorer Sleeper Retaining Walls Installation and Technical Guide (2023) (checked 2026-10-01)
Post spacing = sleeper length + 30 mm (2030 mm centres for 2000 mm sleepers)	30 mm	Austral Masonry, Explorer Sleeper Retaining Walls Installation and Technical Guide (2023) (checked 2026-10-01)
Post spacing = sleeper length + 15 mm (1815 mm for 1800 mm timber sleepers)	15 mm	Galintel, Retaining Wall Post Selection & Installation Guide (checked 2026-10-01)
Minimum pier embedment 1.0 m for walls up to 1.0 m, then 1.2, 1.4 and 1.6 m for walls up to 1.2, 1.4 and 1.6 m; taller walls take the deeper of the table's two values	1 m minimum	Austral Masonry, Explorer Sleeper Retaining Walls Installation and Technical Guide (2023) (checked 2026-10-01)
Minimum 100 mm of concrete below the post	100 mm	Galintel, Retaining Wall Post Selection & Installation Guide (checked 2026-10-01)
Post holes 450 mm in diameter	450 mm	Galintel, Retaining Wall Post Selection & Installation Guide (checked 2026-10-01)
100 series posts in 0.9 to 3.6 m lengths in 0.3 m steps	0.9 m shortest	Galintel, Retaining Wall Post Selection & Installation Guide (checked 2026-10-01)
Premixed concrete, 20 kg bags needed for one cubic metre	110 20 kg bags per m³	Cement Australia slab calculator (checked 2026-09-21)
300 mm of 20 mm crushed rock behind the wall to 200 mm from the top, Ø100 slotted ag pipe at 1 in 100 (max 30 m run), filter fabric, 100 mm soil plug	300 mm	Austral Masonry, Explorer Sleeper Retaining Walls Installation and Technical Guide (2023) (checked 2026-10-01)
Lean the wall back at least 30 mm for every 1.0 m of height	30 mm per m	Austral Masonry, Explorer Sleeper Retaining Walls Installation and Technical Guide (2023) (checked 2026-10-01)
Walls over 1 m or carrying loads such as structures or pools may need an engineer's design	1 m	Timber Preservers Association of Australia, Technical Note 4 (checked 2026-10-01)
WA (City of Vincent): retaining walls over 500 mm need a building permit	0.5 m	City of Vincent, Retaining wall (checked 2026-10-01)
NSW: exempt only up to 600 mm above existing ground and at least 1 m from a boundary	0.6 m	Wollondilly Shire Council, Retaining Walls Fact Sheet (2024) (checked 2026-10-01)
QLD (Brisbane): no approval only if 1 m or less, no load behind it, and 1.5 m from a building or another wall	1 m	Brisbane City Council, Retaining wall (checked 2026-10-01)
VIC (Boroondara): a building permit is always needed over 1 m	1 m	City of Boroondara, Retaining wall permits (checked 2026-10-01)

Manufacturers named here are the source of the number, not a recommendation. Confirm quantities with your supplier.

Frequently asked questions

Stop typing measurements in by hand

MetreMate measures every wall, floor and roof straight off your PDF plan. Then it hands you the same numbers this calculator asks for.

Try MetreMate free