Concrete Block Fill Calculator

How this is calculated

The main output is the number of bags needed, based on the wall’s net fill volume divided by the chosen bag yield. The supporting numbers show the total fill volume in litres and the same volume in cubic feet. The volume maths starts by finding the wall area and dividing by the block face area to estimate the number of blocks in the wall. The fill volume then uses a published grout volume per filled cell for standard hollow CMU units, rather than multiplying wall area by block face area. General Shale's 'Concrete Block Grout Fill Quantities' table lists 29.7 cubic feet (1.10 cubic yards) of void volume per 100 square feet of wall for 8-inch Stretchers; 29.7 / 225 = 0.132 cubic feet per filled cell. These are calculated void volumes with no allowance for waste, settlement, or workmanship. For standard hollow concrete masonry units, the nominal block face is 16 in × 8 in, and the common modular joint size is 3/8 in; those dimensions are published in ASTM C90 / ASTM C140 references used by CMU manufacturers and masonry guides. Bag yield must come from the product you plan to buy. Different grout and concrete mixes have different published yields, so the calculator treats bag yield as an input rather than inventing a coverage constant. This tool excludes rebar displacement, bond beams, and waste from spillage or overfill. If your wall has reinforced cells only, you should reduce the fill volume manually before buying.

Common questions

Does this count mortar joints too?

No. It estimates the fill inside the hollow blocks only, not mortar in the bed or head joints.

What bag yield should I use?

Use the yield printed on the exact grout or concrete bag you plan to buy.

Where does the 0.132 per-cell volume come from?

General Shale's Concrete Block Grout Fill Quantities table lists 29.7 cubic feet (1.10 cubic yards) of void volume per 100 square feet of wall for 8-inch Stretchers; 29.7 / 225 = 0.132 cubic feet per filled cell. These are calculated void volumes with no allowance for waste, settlement, or workmanship.

Take it further with AI

Copy this into ChatGPT or Claude with your own numbers filled in. It hands over the figures this calculator worked out, so the answer is built on real arithmetic instead of a guess.

I used the Concrete Block Fill Calculator at https://www.bfcbrilliance.com/tools/concrete-block-fill-calculator.

What I entered:
- Wall length (ft): ___
- Wall height (ft): ___
- Block length (in): ___
- Block height (in): ___
- Cells per block: ___
- Bag yield (ft³): ___

What it calculated:
- Bags to buy: ___
- Total fill volume: ___
- Total fill volume: ___

Use those figures as given — they are already worked out, so please don't recalculate or estimate your own. Help me turn them into a plan: what to buy or do, in what order, roughly what it should cost, and the mistakes people most often make with this job.

Where the job touches structure, gas, or electrics, tell me to check local building code and whether a permit or a licensed trade is required.

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