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

Estimate the blocks for a retaining wall. Enter the wall length and height and the size of one block, and the calculator shows the blocks per row, the number of rows, and the total. Remember a wall also needs a base, drainage, and often consent and engineering for taller heights.

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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