Calculate block core fill concrete or grout for a CMU or 200 series block wall from wall size or block count, using typical core volumes per block size.

Uses 1.125 blocks per ft² for 8 × 16 in faces, or 12.5 per m² for 200 series. Core volumes are typical; your block’s data sheet is more exact.

Total fill volume of all cores in one block, from its manufacturer.

Openings, allowances and bag estimate
Blank means no openings. Subtract doors and windows from gross wall area.

Blank means 0%. Use a project-specific percentage of filled core volume.

Blank means 0%. Choose a project-specific allowance.

Optional: blank omits bag count. Use the mixed yield printed on your chosen grout product, not a universal bag-weight conversion.

Related Calculators

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 × vb × (F) / (100) × (1 - (R) / (100)) × (1 + (W) / (100))

Variables:

  • V is the estimated grout (core fill) volume
  • N is the estimated number of blocks in the wall
  • vb is the grout volume per fully filled block: a typical value for the chosen block size, or your manufacturer’s figure
  • F is the percent of cores filled (%)
  • R is the rebar displacement (%)
  • W is the waste/overage (%)

In wall-size mode, N = (length × height − opening area) × 1.125 for nominal 8 × 16-inch block faces (12.5 blocks per m² for 200 series), with area in ft². Block-count mode accepts installed block equivalents directly. Grout volume depends on the net core volume of the actual product. Optional displacement and overage default to zero; bag count is omitted until a product yield is supplied. There is no rectangular-volume tab.

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.