CalcRetaining Wall Block & Base Calculator
Last updated: 2026-08-24
How to Use This Calculator
This calculator helps you plan the materials for a segmental retaining wall. Start by measuring the total length of the wall in meters and the desired height of the exposed wall. The height should be measured from the top of the base course to the top of the wall. Input these values into the calculator. If your blocks have different dimensions than the default (0.45m length and 0.20m height), adjust them accordingly. The calculator will then compute the total number of blocks required, accounting for the fact that you need to round up to whole blocks. Additionally, it calculates the volume of gravel needed for the base, using a standard base width of 1.5 times the block length and a compacted depth of 0.15 meters. Finally, it estimates the number of geogrid layers needed, which is typically one layer for every 0.6 meters of wall height. For walls under 0.6 meters, no geogrid is required.
Formula and Methodology
The formulas used are straightforward. The number of blocks is found by dividing the wall length by block length and the height by block height, then multiplying the two results (rounded up). For gravel volume, the base width is assumed to be 1.5 times the block length, multiplied by the wall length and a depth of 0.15 meters. Geogrid layers are calculated as the ceiling of (height / 0.6) minus one, with a minimum of zero. This method is based on common DIY and professional standards, but real-world conditions may vary.
Practical Examples
Example: You have a wall length of 10 meters and height of 1.2 meters. Using default block sizes (0.45m x 0.20m), the calculator will give you about 134 blocks (rounded up). The gravel base volume would be 1.0 m³ (10m * 0.675m * 0.15m). Geogrid layers would be 1 (ceil(1.2/0.6) - 1 = 2-1 = 1). So you would need 134 blocks, 1.0 m³ of gravel (add extra for compaction), and 1 layer of geogrid.
Tips and Best Practices
Always add a 10-15% waste factor to your block and gravel order. For the base, compact the gravel in 15cm lifts. Ensure the base is level and wide enough to support the wall. For walls over 1.2m, consult a structural engineer. Use geogrid as specified by the manufacturer. When calculating, measure the wall length along the front face, not the excavation length. Keep records for future reference.
FAQ
How do I determine the block size?
Check the manufacturer's specifications. Common block sizes are 0.45m x 0.20m, but many variations exist. The calculator uses these as default, but you can adjust them to match your specific block.
What is geogrid and when is it needed?
Geogrid is a reinforcement layer typically used for walls taller than 0.6m. It helps stabilize the soil behind the wall. Our calculator estimates the number of layers, but consult an engineer for specific requirements.
How much gravel should I order?
The calculator gives the volume of gravel needed for the base. It's wise to add 10-15% extra for compaction and settling. For a 10m long wall, you'll need about 1.0 m³ of gravel.