How to use the masonry core fill mortar calculator
Type the block length, height and thickness, the volume of a single core and the number of cores in each block, the share you actually fill, and the block count. The page returns the volume of mortar or grout needed to fill those cores, together with the share of the block that the cores take up, so you can sanity-check the core volume you entered.
The arithmetic multiplies core volume by fill share and block count. Inch sizes are kept in cubic inches per block and totals are shown in cubic feet and cubic yards, current as of October 2026. Multiplying volumes is a definition rather than a standard, so no outside source is needed.
Core volumes for particular block sizes and a waste allowance were not confirmed in an authoritative source; webs differ between makers, so no value is suggested. Joint mortar, brick and block counts, and mix proportions are not covered. This calculator is for reference and does not replace design. Review by a qualified engineer is required.
Frequently asked questions
Take it from the block maker product data and type it in. Core volumes by block size were not confirmed in an authoritative source, and two blocks with the same outside size can differ in their webs, so no figure is offered here.
No. The page covers only the mortar or grout that fills the block cores. Joint mortar and brick or block counts are not covered, so work those out separately from the wall area and joint thickness.
Use 100 if every core is filled, or the matching share if only the reinforced cells are. Which cells get filled is set by the design and the method of work, so the page suggests no share and applies only what you type.