Which cores get filled
Structural walls fill every core containing rebar — typically verticals every 4 feet and all corner and opening cores. A standard 8×8×16 block has two cores; filling one block takes about <strong>0.25 cubic feet</strong> of grout or concrete. The calculator multiplies your block count by that volume and converts to bags and yards.
Grout consistency matters
Core fill is poured, not placed — it must flow to the bottom of every cavity without honeycombing. Fine grout (small aggregate) pumps easily; if you're using bagged concrete as fill, expect to add water to a soupy consistency and rod every core. Fill in lifts of about 4 feet so the grout doesn't blow out the block faces.