How Much Concrete is Needed to Fill Cinder Blocks?
Filling the hollow cores of cinder blocks with concrete grout is a standard requirement for structural, retaining, and foundation walls. This process, often called "grouting," significantly increases the wall's compressive strength and lateral resistance. Calculating the exact volume of concrete needed is essential to avoid under-ordering from a ready-mix truck or hand-mixing too many bags.
Core Fill Estimation Rule
The volume of concrete required depends on the block's width and whether you are doing a "full grout" (filling every core) or a "partial grout" (filling only cores with rebar). For a standard 8x8x16 cinder block, it takes approximately 0.22 cubic feet of concrete to fill both hollow cores.
Yield Per Cubic Yard
~120 Blocks
One cubic yard of concrete grout will fill approximately 120 standard 8-inch blocks.
Yield Per 80lb Bag
~2.5 Blocks
One 80lb bag of pre-mixed concrete yields about 0.60 cubic feet, enough for 2.5 blocks.
How to Calculate Grout Volume
- Determine Number of Blocks to Fill: Decide if you are filling all blocks or just specific ones (e.g., every 32 inches).
- Calculate Total Cubic Feet: Multiply the number of blocks by 0.22 (for 8-inch blocks).
- Convert to Cubic Yards: Divide the total cubic feet by 27.
- Add Waste: Always add 5-10% for "spillage" and "blowout" during the pour.