Concrete Block Fill Calculator

A concrete block fill calculator returns the cubic feet and 80 lb bags of core-fill grout needed for CMU block cores. It counts cells from wall length and core spacing. It then multiplies by wall height and a QUIKRETE-based grout volume per foot, adds a 10% waste allowance by default, and rounds up to whole bags.

Last reviewed September 2026Method & sources Report an error

Not to scale.

Cells to Fill

Includes a 10% waste allowance.

Shopping list

Core-fill grout (coarse)36 80 lb bagsFills 8 cells.

Breakdown
Cells to Fill	8
Grout Needed (with waste)	22.9 cu ft
Grout Bags (80 lb)	36
Estimated Cost

How to Calculate Concrete Block Fill

Grouted cores run as continuous vertical columns from the base of the wall to the top. The spacing follows your plan: every core for a solidly grouted wall, or every 16, 24, 32, or 48 in. for partial grouting at reinforcement. The number of cells to fill is the wall length, in inches, divided by the spacing, rounded up. Each cell's volume is that count times the full wall height. QUIKRETE's Core-Fill Grout data sheets state that one 80 lb bag fills the cores of about 3 standard 8x8x16 blocks. Coarse yields approximately 0.65 cu ft per bag, and Fine about 0.68 cu ft. Since a standard block is 8 in. (0.667 ft) tall, that works out to roughly 0.325-0.34 cu ft of grout per linear foot of a continuous core. Multiply that by the total core height to get the raw grout volume. Then add a waste allowance for spillage and minor cell irregularity, divide by the bag yield, and round up to a whole bag.

Example: 20 ft long, 8 ft tall wall

A 20 ft long, 8 ft tall wall, grouting every 32 in. on center with Coarse grout, at 10% waste: 1. Cells to fill: (20 × 12) ÷ 32 = 7.5, rounded up to 8 cells 2. Total core height: 8 × 8 ft = 64 linear ft 3. Grout per linear ft (Coarse): 0.65 cu ft ÷ 3 blocks ÷ 0.667 ft per block = 0.325 cu ft/ft 4. Raw grout volume: 64 × 0.325 = 20.8 cu ft 5. With 10% waste: 20.8 × 1.10 = 22.88 cu ft 6. Bags: 22.88 ÷ 0.65 = 35.2, rounded up to 36 bags (80 lb Coarse Core-Fill Grout) Switching to solid grouting (every 8 in.) on the same wall would raise the cell count from 8 to 30, to roughly 132 bags. That's a good illustration of why partial grouting at just the reinforced cells is far cheaper when the design allows it.

Concrete Block Fill: Compare Scenarios

Scenario	Cells to Fill	Grout Needed (with waste)	Grout Bags (80 lb)
Small (10 ft wall, partial grouting at 32 in.)	4	11.4 cu ft	18
Medium (20 ft wall, partial grouting at 32 in.)	8	22.9 cu ft	36
Large (60 ft wall, solid grouting)	90	257.4 cu ft	396

What Is Concrete Block Fill?

A concrete block fill calculator estimates the grout needed to fill the hollow cores of a CMU wall. It covers either just the cells with vertical reinforcement (partial grouting) or every core (solid grouting). It exists because grout is bought and mixed by volume or bag count, not by "number of cores." The volume per core also isn't obvious from the block's outside dimensions. The cores are hollow, tapered space inside the face shells and webs, which is why this calculator starts from a manufacturer's actual fill-rate data rather than the block's overall footprint.

Concrete Block Fill: Pros and Cons

Pros

Starts from a manufacturer's stated fill rate (blocks per bag) rather than an assumed core geometry, so the volume figure is grounded in a real product's data sheet
Supports partial grouting (reinforcement-only) as well as solid grouting, since the spacing input covers both. Most competitor calculators only handle a solidly grouted wall
Applies a waste allowance for spillage and cell irregularity automatically instead of leaving it to guesswork

Cons

Assumes standard 8x8x16 two-core units with unobstructed, aligned cores. Bond beam courses, lintel units, and any knocked-out webs add grout volume this calculator does not separately account for
Doesn't select fine vs. coarse grout for you. That depends on your grout space dimensions and pour height (see NCMA TEK 3-2A's grout space requirements table), so it's a design decision, not a formula this tool makes
A different core-fill grout product may publish a different yield per bag than the QUIKRETE figures used here

Concrete Block Fill: What a Pro Checks

Match grout type to your cell size and pour height, not preference. NCMA TEK 3-2A's grout space requirements table sets minimum cell dimensions for each type and the maximum pour height. Check your actual dimensions before choosing coarse or fine.
Vibrate or puddle every grout lift right after placing it. NCMA TEK 3-2A calls for consolidation immediately after the pour to eliminate voids, and most lifts need a second pass a few minutes later as the block absorbs water from the grout.
Confirm whether your design calls for partial grouting (reinforced cells only) or solid grouting before you order. The bag count between the two is large, since solid grouting fills every core instead of just the ones spaced for rebar.

Frequently Asked Questions

How much grout does it take to fill one concrete block core?

About 0.22 cubic feet, based on QUIKRETE's Core-Fill Grout data sheets. Those sheets state that one 80 lb bag yields roughly 0.65-0.68 cu ft (Coarse or Fine) and fills the cores of approximately 3 standard 8x8x16 blocks.

Should I use fine or coarse grout?

That depends on the width of your grout space and pour height, not on preference. NCMA TEK 3-2A's grout space requirements table (drawn from the Specification for Masonry Structures) sets minimum cell dimensions for each grout type and maximum pour height. Fine grout is generally used for narrower cells. Coarse grout needs a larger, coarser-aggregate-friendly space. Check your specific cell dimensions and pour height against that table, or ask your structural engineer.

What's the difference between solid grouting and partial grouting?

Solid grouting fills every core in the wall (enter 8 in. spacing here). It's typically done when reinforcement is closely spaced or there are many bond beams, since it can be faster than grouting cells individually. Partial grouting fills only the cells that contain vertical reinforcement, at whatever spacing the design calls for (commonly 16-48 in. on center). It uses far less grout, as the worked example above shows.

Does this include grout for bond beams or lintels?

No. This calculates vertical core fill only. A horizontal bond beam or lintel course is a different shape (a U-shaped channel the width of the wall) and needs its volume calculated separately based on the beam's length, width, and depth.

Why does the grout volume divide by 3 blocks per bag instead of a cubic-foot core volume?

Both numbers come from the same manufacturer figure. The data sheet states the bag's total yield in cubic feet and separately states it fills about 3 block cores. Dividing the cubic-foot yield by 3 backs out the average volume per core. It's the same fill-rate information, just expressed two ways for the calculator's underlying math.

Do I need to vibrate or consolidate the grout after pouring?

Yes, per standard masonry grouting practice (NCMA TEK 3-2A). Consolidation by vibration (or puddling for pours of 12 in. or less) is required immediately after placement to eliminate voids. Most lifts need reconsolidation a few minutes later as the units absorb water from the grout. This calculator only estimates material quantity, not the placement procedure.

Sources

Concrete & Masonry