Free Block Fill Calculator — Yards & Bag Count (2026)

How to Use This Calculator

1. 1Count the total number of CMU blocks that need to be filled — include all courses and wall sections.
2. 2Select the block size: 8-inch is standard residential, 10-inch and 12-inch are used for taller or load-bearing walls.
3. 3Choose the fill type: concrete/grout for structural fills, vermiculite for insulation, foam insulation for thermal performance.
4. 4Click Calculate to get cubic yards, cubic feet, and bag count.

About This Material

Block fill (also called core fill or grout fill) is the process of filling the hollow cores of concrete masonry unit (CMU) blocks with concrete, grout, vermiculite, or foam insulation. Structural block fill uses a pourable concrete or fine-grout mix (typically 2,000 to 3,000 PSI) that flows into the cores and around any rebar placed inside the wall. The International Building Code (IBC) and most local codes require grouted cells at specific intervals — usually every 48 inches horizontally and at all corners, jambs, and bond beam courses. Rebar placement is critical for structural integrity. Vertical rebar (#4 or #5 bars) is set into the footing before the wall is laid and extends up through the cores that will be grouted. Horizontal rebar runs through bond beam blocks at the top of the wall and at intermediate courses as specified by the engineer. All grouted cells must have rebar — filling empty cores with grout alone does not meet structural requirements in most jurisdictions. For non-structural applications, vermiculite or perlite loose fill provides moderate insulation (R-value of about 2.1 per inch) and is poured dry into the cores. Spray foam insulation offers higher R-values (R-6 per inch for closed-cell) but costs significantly more and requires professional installation. Standard 8-inch CMU blocks have two cores, each roughly 5.5 inches wide by 7.5 inches tall by 3.25 inches deep, yielding approximately 0.009 cubic yards of fill per block. The 10-inch and 12-inch blocks have proportionally larger cores. Expect to pay $120 to $160 per cubic yard for ready-mix grout delivered, or $5 to $7 per 80-pound bag of premixed concrete for small projects. Vermiculite costs $15 to $25 per 4-cubic-foot bag. Always over-order by 10% to account for settling, spillage, and irregular core sizes.

Installation Tips

• •Pre-wet the CMU cores before pouring grout — dry blocks absorb water from the mix and weaken the fill.
• •Pour grout in lifts of no more than 4 feet (5 courses) at a time, then consolidate with a vibrator or rod.
• •Use fine grout (3/8-inch aggregate max) so it flows freely through the cores without bridging.
• •Place vertical rebar before laying blocks and brace it plumb — do not try to drop rebar into filled cores.
• •Install cleanout blocks at the base of tall walls so you can inspect cores before grouting.
• •Fill bond beam courses completely and rod the grout to eliminate voids around horizontal rebar.

Common Mistakes to Avoid

• ⚠Grouting all cores at once on a tall wall — grout sets under pressure and can blow out lower courses. Limit pours to 4-foot lifts.
• ⚠Skipping rebar in grouted cells — ungrouted cores are hollow, but grouted cells without rebar provide little structural value.
• ⚠Using standard concrete mix instead of fine grout — large aggregate bridges across the core opening and creates voids.
• ⚠Not consolidating grout with a vibrator or rod — air pockets reduce bond strength by up to 50%.
• ⚠Filling cores in freezing temperatures — grout must cure above 40 degrees F for at least 48 hours.

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