Retaining Wall Block Calculator

This calculator works out how many blocks you need to build a retaining wall in New Zealand, from the wall length and height and the face size of your chosen block, plus a small allowance for cuts and breakages. Whether you are using keystone-style interlocking blocks, besser blocks or concrete units, the principle is the same: the number of blocks is set by how much wall face you have to cover and how big each block's face is. Working it out before you order saves both the cost of over-buying heavy, awkward blocks and the delay of running short partway up the wall. The maths is simply the wall face area, length times height, divided by the face area of one block, and rounded up. You enter the wall length and height in metres and the block face length and height in millimetres, plus a waste allowance, and the calculator returns the number of blocks needed along with the wall face area. As a guide, many retaining blocks have a face around three hundred by two hundred millimetres, but they vary a lot, so use the real dimensions from your supplier's spec sheet. Importantly, retaining walls over about 1.5 metres or carrying extra load usually need a building consent and engineering in New Zealand, so check with your council before you build. An estimate for the block quantity only.

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Use your block's real face size from the spec sheet. Walls over about 1.5 m or carrying load usually need consent and engineering. An estimate for quantity only.