Use the tabs in the calculator to (1) calculate the volume of a rectangular space, (2) estimate grout needed to fill CMU (concrete block) cores in a wall, (3) estimate block count, and (4) convert a volume to an estimated number of bags.
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Block Core Fill Formula
The following formula can be used to estimate grout (core fill) volume for a CMU wall based on an estimated block count and an estimated grout volume per block.
V = N \times v_b \times \frac{F}{100} \times \left(1-\frac{R}{100}\right) \times \left(1+\frac{W}{100}\right)Variables:
- V is the estimated grout (core fill) volume
- N is the estimated number of blocks in the wall
- vb is the typical grout volume per fully grouted block (varies by block thickness and manufacturer)
- F is the percent of cores filled (%)
- R is the rebar displacement (%)
- W is the waste/overage (%)
For a simple rectangular space (the “Rectangular Volume” tab), the volume is calculated using V = L × W × H, where L, W, and H are the inside dimensions of the space being filled. For CMU core fill specifically, grout volume depends on the net void volume of the block cores (often approximated using a per-block grout volume).
What is a Block Core Fill?
A Block Core Fill is a construction process where the hollow spaces or cores in concrete blocks or masonry units are filled with a cement-based mixture, often referred to as grout. This is done primarily to increase the structural capacity and stability of the wall and to provide a solid matrix around reinforcement. Filling cores can also improve sound reduction and increase thermal mass, but fully grouting typically reduces the insulating value compared with leaving the cores hollow. The grout can be poured or pumped into the blocks, and it typically contains cement, sand, and water.
