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Hollow Block Core Fill Volume

Estimate concrete core fill from shell and web geometry, wall coverage and a waste allowance.

  • Formula & worked example
  • Private in your browser
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

A 4 m by 2 m wall using 40 cm by 20 cm block faces needs 100 blocks. With the selected 20 cm block preset and zero waste, the rectangular core estimate is 0.918645 m³ of fill.

Core volume = (block width−2 end webs−inner webs)×(block thickness−2 shells)×block height; wall fill = core volume×wall area/block face area.

Worked example

Enter these known values and leave the other values blank.

Wall width
4 m
Wall height
2 m
Wastage
0 %
Block width (w)
40 cm
Block height (h)
20 cm
Block thickness (t)
20 cm
End web thickness (we)
3.175 cm
Shell thickness (s)
3.175 cm
Volume of core per block
9186 cm³
Number of blocks needed
100
Fill volume
0.9186 m³
Final volume
0.9186 m³

Assumptions and limitations

  • Blocks use rectangular cores and effective face coverage. Select the custom block option for measured shells and webs; preset dimensions are illustrative. The web count convention is two end webs plus the selected number of inner webs. Wall openings, joints, reinforcement displacement and block cuts are excluded. Waste must be nonnegative.
  • Select compatible units and clear the quantity to solve before supplying the remaining measurements. Rounded purchase counts cannot uniquely recover a continuous dimension. Currency choices label amounts and do not convert exchange rates.

Common questions

How can I solve for a missing measurement?

Clear that field, then enter independent known values. Lock a known measurement to preserve it while changing another value. Procurement counts are rounded upward and cannot be reversed uniquely.

References

Enforce the stated physical and discrete input domains. Bookify replaces the captured rounded US gallon with the exact 3.785411784-liter definition.

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