Retaining Wall Block Calculator

Start by entering the total length and height of your retaining wall. If you have a curved wall, measure the total run along the face. For stepped walls, calculate each level separately and add the results together.

Next, choose your block size. The three presets cover the most common interlocking landscape blocks sold at home improvement stores. If your block has different dimensions, switch to custom and enter the width (the face you see), height (how tall each course is), and depth (how far the block goes into the hillside).

The options section lets you toggle cap blocks on or off, adjust the waste factor, and set the backfill and base gravel depths. The default values work well for most residential walls, but you can fine tune them to match your site conditions or your block manufacturer's recommendations.

Results update instantly as you type. You will see the total block count, number of courses, all supporting materials including drainage pipe and filter fabric, and a full cost breakdown with a comparison to professional installation pricing.

The calculator divides your wall height by the block height to determine how many horizontal rows (courses) you need. It then divides the wall length by the block width to determine how many blocks fit in each course. Multiplying courses by blocks per course gives the raw block count before waste.

Both of these divisions round up to the next whole number because you cannot install a partial block in the field. The waste factor (default 10%) accounts for cuts at corners, breakage during handling, and blocks that arrive damaged. For walls with curves or multiple corners, consider increasing waste to 15%.

The most common reason retaining walls fail is water pressure behind the wall, not the weight of the soil. When rain saturates the soil behind a wall, it can double or triple the lateral force pushing against the blocks. Gravel backfill creates a drainage channel that lets water flow down to the perforated drain pipe at the base instead of building up behind the wall.

The calculator defaults to 12 inches of backfill depth, which is the standard recommendation for residential walls up to 4 feet tall. The base gravel trench defaults to 6 inches deep and extends 3 inches beyond each side of the block. This gives you a level, compacted foundation that prevents settling and keeps the first course straight over time.

Standard interlocking blocks (12 inches wide by 4 inches tall) are the most popular choice for residential walls. They are light enough for one person to handle, widely available at Lowe's and Home Depot, and come in a range of colors and textures. These blocks work well for walls up to about 2 feet tall without any additional reinforcement.

Large format blocks (18 by 6 inches or bigger) go up faster and create a bolder look, but they weigh significantly more per unit. For walls between 2 and 4 feet, larger blocks can be a better choice because they provide more mass to resist soil pressure. Some manufacturers also require geogrid reinforcement for walls over a certain height. Check the block manufacturer's installation guide for specific requirements.

Small blocks (8 by 3 inches) are best for decorative garden borders and low landscape edging under 18 inches tall. They cost less per block but require more blocks and more courses to reach the same height, so the total cost difference is often minimal.