Concrete Block Fill Calculator
Determine exactly how much grout or concrete you need to fill hollow concrete masonry unit (CMU) walls. Select your block size, core fill pattern, and get precise material quantities with cost estimates.
Total length of the block wall
Height of the block wall
Nominal width of the CMU block
Fill Volume: Blocks x Core Vol per Block x Fill Fraction
Approximate Core Volumes:
4″ block: 0.10 cu ft each
6″ block: 0.28 cu ft each
8″ block: 0.34 cu ft each
10″ block: 0.52 cu ft each
12″ block: 0.68 cu ft each
Area = 400 sq ft
Blocks = 400 x 1.125 = 450 blocks
Fill Volume = 450 x 0.34 = 153 cu ft
In Yards: 153 / 27 = 5.67 cu yds
With 10% waste: 6.24 cu yds
80lb bags: approx. 281 bags
How much concrete does it take to fill a standard concrete block?
A standard 8"x8"x16" concrete block has a core volume of approximately 0.17 cubic feet per core. Since standard blocks have two cores, each block requires about 0.34 cubic feet of fill. However, actual fill volume depends on whether you use half blocks, bond beams, or have rebar occupying space.
Should I fill all cores or only certain ones?
For load-bearing walls, typically every core that contains vertical reinforcement must be filled. For non-load-bearing walls, you may only need to fill cores at specific intervals (every 4-6 feet) or at bond beam locations. Always consult your structural engineer for specific requirements.
What is the difference between grout and concrete for filling blocks?
Grout for block fill has a higher slump (flowability) than standard concrete — typically 8-10 inches versus 3-4 inches for concrete. Grout also uses smaller aggregate (3/8" max) to flow freely through block cavities. Using standard concrete can result in voids and poor consolidation.
How do I calculate block fill for a wall with openings?
Calculate the total wall area, then subtract all window and door openings. Multiply the net wall area by the number of blocks per square foot (1.125 blocks per sq ft for 8"x8"x16" blocks). Then multiply by the fill volume per block (approximately 0.34 cubic feet for standard blocks).
🔗 Related Calculators
📐 Formula
Fill Volume: Blocks x Core Vol per Block x Fill Fraction
Approximate Core Volumes:
4″ block: 0.10 cu ft each
6″ block: 0.28 cu ft each
8″ block: 0.34 cu ft each
10″ block: 0.52 cu ft each
12″ block: 0.68 cu ft each
📝 Example Calculation
Area = 400 sq ft
Blocks = 400 x 1.125 = 450 blocks
Fill Volume = 450 x 0.34 = 153 cu ft
In Yards: 153 / 27 = 5.67 cu yds
With 10% waste: 6.24 cu yds
80lb bags: approx. 281 bags