How many blocks do I need for a retaining wall?

Divide the wall length by the block length to get blocks per row, and the wall height by the block height for the number of rows. Multiply the two for the total. The calculator does this from the dimensions you enter.

Do I need council consent for a retaining wall?

In New Zealand a building consent is generally needed for retaining walls over 1.5 metres high, or lower walls that carry extra load such as a driveway. Always check with your local council before you start, as rules vary.

What else do I need besides blocks?

A retaining wall also needs a compacted base, drainage metal and pipe behind it, and often geogrid or posts for taller walls. This calculator estimates the blocks only, so factor in those extras and get engineering advice for higher walls.

Retaining Wall Calculator

This calculator works out how many concrete blocks you need to build a retaining wall, so you can price the job and order the right quantity before you start. You enter the wall length and height in metres, plus the length and height of the block you plan to use in millimetres, matching the size sold by your local supplier. From these figures it returns the total number of blocks needed, the blocks per row, and the number of rows required to reach your wall height, so you can see how the total is built up. Each row and block count is rounded up to the next whole block, since you cannot buy a fraction of one, and the figure does not allow for corners, curves or steps, which typically need a few extra blocks. Retaining walls need more than blocks alone. Budget for a compacted hardfill base, drainage metal and a perforated pipe behind the wall to relieve water pressure, and for taller walls, geogrid reinforcement or posts. In New Zealand a building consent is generally required once a wall passes 1.5 metres in height, or for lower walls carrying extra load such as a driveway, so check with your council before you build. This is a materials estimate only, so confirm quantities with your supplier and get engineering advice for anything beyond a straightforward low wall.

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Wall length (m)

Wall height (m)

Block length (mm)

Block height (mm)

0 blocks

blocks needed

Per row0

Rows0

Blocks only. Add base course, drainage metal and pipe, and get advice for walls over 1.5 m.

How it works

Blocks per row is the wall length divided by the block length. The number of rows is the wall height divided by the block height. Multiplying the two gives the total, rounded up to whole blocks. Curved or stepped walls and corners may need a few more.

Worked example

An 8 metre wall, 0.9 metres high, with 295 by 150 mm blocks needs about 28 blocks per row and 6 rows, which is around 168 blocks.

Related calculators

Concrete Calculator: concrete for footings.
Gravel Calculator: drainage metal.
Brick Calculator: bricks for a wall.
Fencing Calculator: posts and palings.

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