Retaining Wall Block Calculator

Turn the block count into a complete material order

The block subtotal below excludes aggregate and other components. Before asking for delivery, split the order into installed blocks, caps, base aggregate, block-core fill, wall-back aggregate and the other items shown on your design. Use the exact block system and approved layout for each quantity.

The Allan Block material worksheet treats base aggregate and the core/consolidation zone separately and refers reinforcement and drainage details to the plans. Its system-specific dimensions and material specifications are not defaults for every retaining wall.

Three aggregate quantities to keep distinct

Base

Multiply its designed length × width × thickness. Use feet throughout and divide cubic feet by 27 for cubic yards. Do not use wall-face area as base volume.

Behind the wall

Use the actual aggregate-zone cross-section and height. If calculating a separate rear rectangle, begin at the back of the block so it does not include the block body or cores again. Split changes in height or depth into separate sections.

Inside the blocks

Use the manufacturer's fill volume per installed hollow unit, or its documented combined core-and-rear-zone estimate. Do not estimate hollow space from the external block dimensions. If a supplied figure already includes cores and rear aggregate, do not add core fill a second time.

An original, checkable order example

Assume a plan supplies these hypothetical quantities: a 20 ft base, 2 ft wide and 0.5 ft thick; a separate rear aggregate zone 20 ft long, 1 ft thick and 2.5 ft high; and 75 installed hollow blocks needing 0.20 cu ft each. These values demonstrate an order, not a wall design or a real block's core capacity.

• Base: 20 × 2 × 0.5 = 20 cu ft.
• Rear zone, excluding block bodies: 20 × 1 × 2.5 = 50 cu ft.
• Cores: 75 × 0.20 = 15 cu ft.
• If all three use the same approved aggregate and volume basis: 85 cu ft ÷ 27 = 3.148148 cu yd. A separately chosen 5% handling allowance gives 3.305556 cu yd.

At a hypothetical supplier increment of 0.5 cu yd, the actual bulk purchase is 3.5 cu yd. At 0.5 cu ft per bag, the alternative is 179 bags. These alternatives must use the same material and a valid delivery-volume conversion; the example assumes factor 1. Spare blocks bought for breakage are not installed units to fill. For example, ordering 83 blocks does not change the planned 75 cores to 83.

Carry the quantities into the purchase planner

Open the multi-area aggregate purchase worksheet. Its arithmetic can be used for your specified wall aggregate; this does not mean you should buy paving-base material. Enter three rows: Base 20 × 2 ft at 6 in; Rear zone 20 × 1 ft at 30 in; and Core-volume equivalent 15 × 1 ft at 12 in. The last row is an explicitly labeled 15 cu ft equivalent, not a real trench. Use zero exclusions, 5% extra, factor 1, bag yield 0.5 and bulk increment 0.5. Replace every assumption with your confirmed specification before ordering.

If the materials differ, run separate worksheets. If the manufacturer supplies a combined core-and-rear estimate, use it once instead of those two rows. Ask whether that figure already contains a delivery adjustment or reserve before adding either again.

Complete the quote before comparing totals

Attach the downloadable wall-order brief to the block estimate and aggregate export. It records caps, adhesive, drain pipe, specified reinforcement, delivery and missing prices separately. An unpriced item is unresolved, not free. Do not use this quantity workflow to choose reinforcement, drainage outlets, foundation dimensions or wall height.

Wall purchase workflow reviewed November 4, 2026. Hypothetical example; no construction or engineering approval implied.

Material-choice review: November 2, 2026. These are planning choices, not a site inspection or a drainage specification.