How this calculator works
Multiply the number of filled units by their open core capacity. Wall mode rounds up a nominal face-area estimate. Geometry mode treats shells and webs as straight, constant-thickness walls; real tapered cores should use manufacturer grout tables. Reverse modes use net volume before waste. The result excludes bond beams, reinforcement displacement, mortar protrusions and any cells left unfilled.
Formula
Core volume = [block length - 2 x end web - (web count - 2) x inner web] x (block thickness - 2 x shell) x block height; net fill = blocks x core volume; order fill = net fill x (1 + waste).
Worked example
One hundred blocks with a measured core capacity of 5 L each need 500 L net fill. A 10% allowance gives 550 L to order. Conversely, 600 L divided among 120 identical blocks implies 5 L per block.
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Frequently asked questions
Can I choose core volume from nominal width alone?
No. Different shells, webs and tapers can produce different core capacities at the same nominal width. Use measured or manufacturer data.
Is every cell assumed to be filled?
Yes. For selective grouting, enter only the equivalent number of fully filled blocks and separately add bond beams or other grout spaces.
Is ordinary concrete always suitable?
No. Masonry grout must meet the project specification and flow into the available spaces. This tool estimates quantity, not material suitability.