CMU core fill and grout estimator

Concrete Block Fill Calculator

This concrete block fill calculator estimates grout for CMU or cinder block cores from a wall size, block count, or filled-core count.

Use this concrete block fill calculator

Start with

Unit:

Wall dimensions

Wall Length (ft)

Wall Height (ft)

Block Size

Core Fill Scope

Waste and product settings

Waste Allowance10%

Use the allowance that matches your project conditions.

Product Bag Yield

Use the mixed-volume yield printed on the product bag. Changing yield affects bag totals only.

80-lb bag yield (cu ft)

60-lb bag yield (cu ft)

Estimate grout allowance and wall budget

Every cell

Which CMU cores are included?

All 12 example cores are included in this planning estimate.

Use the fill pattern specified by your structural drawings. If you know the actual quantity, use Filled cores instead of a spacing estimate.

Example only: standard two-core CMU shown. Bond beams and nonstandard block shapes are not included.

This visual explains grout-volume scope only. It does not specify rebar or structural design.

For 3-web, 4-web, architectural, or other nonstandard CMU, use the manufacturer's core-volume table.

Bond beams, lintels, footings, slabs, and solid walls are not included.

How is the grout volume calculated?

Method reviewed August 2026

The number above is a supplier purchasing benchmark for ordering, not a measurement of the empty cores. Tools that subtract shell and web thickness from an 8x8x16 block often report about 550 cubic inches per block. This page uses 100 standard 8-inch two-core blocks per cubic yard, about 0.27 cubic feet (467 cubic inches) before waste. Those two methods will not match. For 3-web, 4-web, or architectural CMU, use the manufacturer's core-volume table. After that, three inputs decide the result: the standard 16 by 8 inch face, the supplier benchmark for thickness and fill pattern, and the waste allowance you set. Nothing else is inferred. This is a purchasing estimate, not a structural design.

How does wall size become bag counts?

1Standard blocks = ceiling(wall area ÷ 0.889 sq ft)
2Every cell: base volume = blocks ÷ the all-cell blocks-per-cubic-yard benchmark
316, 24, or 32 inch spacing: base volume = blocks ÷ 100 × the matching supplier benchmark
4Order volume = base volume × (1 + waste percentage)
5Bags = ceiling(order volume in cubic feet ÷ product yield)

Where do the benchmark volumes come from?

Every value below is base volume before waste, taken from Westbrook's Grout Calculation for Concrete Block Construction table. Why that table? It is the one supplier matrix that covers every-cell fill and 16, 24, and 32 inch spacing for the same standard two-cell CMU. Two caveats: Westbrook's separate Fine Core Fill product-yield table uses different all-cell figures, so the calculator never mixes the two, and the all-cell and per-100-block values are independently rounded, so small mismatches between columns are normal.

Block thickness	All-cell blocks per cu yd	Every cell per 100 blocks	16 in o.c. per 100 blocks	24 in o.c. per 100 blocks	32 in o.c. per 100 blocks
6 in CMU (6×8×16)	120	0.83 cu yd	0.49 cu yd	0.37 cu yd	0.31 cu yd
8 in CMU (8×8×16)	100	1 cu yd	0.58 cu yd	0.44 cu yd	0.38 cu yd
10 in CMU (10×8×16)	80	1.25 cu yd	0.75 cu yd	0.56 cu yd	0.47 cu yd
12 in CMU (12×8×16)	65	1.54 cu yd	0.9 cu yd	0.68 cu yd	0.57 cu yd

Sources

Want to check the math yourself? These four documents hold the benchmarks, bag yields, and scope limits behind the estimate. Once the volume checks out, the next question is how to buy it.

Westbrook Concrete Block: Fine Core Fill Grout Yields PDF, audited August 3, 2026. The calculator uses only its Grout Calculation for Concrete Block Construction table: the standard two-cell all-cell blocks-per-cubic-yard figures and the 16, 24, and 32 inch per-100-block benchmarks. It does not combine the separate product-yield table.
QUIKRETE Concrete Mix 1101: Product data lists approximate mixed yields of 0.45 cu ft for a 60-lb bag and 0.60 cu ft for an 80-lb bag.
SPEC MIX Core Fill Masonry Grout: Manufacturer information for core-fill grout used in CMU cells and bond beams under the product's stated ASTM C476 scope.
Cemex US Block Calculator: Supplier cross-check that treats block fill as a separate material estimate.

Ready-mix or bags: which number do you order?

It depends on how you buy. Calling a ready-mix or grout supplier? Give them the order volume. Buying bagged material? The calculator divides that same volume by the yield printed on the package and rounds up to whole bags.

Purchase option	Use this result	Before ordering
Ready-mix or bulk grout	Order volume in cubic yards or cubic meters	Ask the local supplier about delivery limits and project-specific allowances.
80-lb bags	Default yield: 0.60 cu ft per bag	Replace the default with the mixed yield on the actual product package.
60-lb bags	Default yield: 0.45 cu ft per bag	Replace the default with the mixed yield on the actual product package.

Product yield controls bag count only. It does not change the calculated grout volume. Always check the package before purchase. The three cases below show how these choices play out with real inputs.

This page calculates grout volume and bag quantity for purchasing. It does not provide live prices, local supplier quotes, or masonry grout price per cubic yard.

Estimate grout allowance and whole-wall budget for a standard CMU wall

Three planning cases that change the order

Same calculator, three different orders. Each case lists the exact inputs, the reproducible output, and a rule you can reuse: how a planning pattern, an actual core count, and a bag yield each change what you buy.

These are illustrative planning cases, not customer results.

Plan selected vertical cores

A small wall has a 24-inch on-center fill pattern in its project documents, but no final filled-core count yet.

Inputs: 20 ft × 8 ft wall; standard 8-inch CMU; Vertical cores 24" o.c.; 80-lb yield 0.6 cu ft; 60-lb yield 0.45 cu ft; 10% waste.
Reproducible output: 0.792 cu yd base; 0.871 cu yd to order; 40 80-lb bags or 53 60-lb bags.
Why this result: The selected-spacing supplier benchmark produces less volume than filling every core in the same wall.
Practical action: Use the order volume for an early supplier conversation, then replace the planning pattern with an actual count when the takeoff is available.
Transferable rule: Spacing is a planning benchmark, not a linear fraction of the every-cell volume.
Use when: Use only when the project documents specify a supported 16, 24, or 32-inch pattern for standard two-core CMU.

Order from an actual core count

The takeoff identifies 144 vertical cores to fill across a standard CMU wall.

Inputs: 144 actual filled cores; standard 8-inch CMU; 80-lb yield 0.6 cu ft; 60-lb yield 0.45 cu ft; 10% waste.
Reproducible output: 0.72 cu yd base; 0.792 cu yd to order; 36 80-lb bags or 48 60-lb bags.
Why this result: The calculator converts the actual count into the equivalent standard two-core block volume, without inferring a spacing pattern.
Practical action: Enter the counted cores before requesting grout so the supplier quantity follows the takeoff rather than an early spacing plan.
Transferable rule: An actual filled-core count takes priority over a spacing approximation when both are available.
Use when: Use for standard two-core CMU only; use manufacturer data for blocks with different core geometry.

Turn volume into bag quantities

A repair needs every core filled in 100 standard blocks, and the crew will buy bagged material instead of ready-mix.

Inputs: 100 standard 8-inch CMU blocks; 80-lb yield 0.6 cu ft; 60-lb yield 0.45 cu ft; 10% waste.
Reproducible output: 1 cu yd base; 1.1 cu yd to order; 50 80-lb bags or 66 60-lb bags.
Why this result: The order volume stays fixed while each package yield converts that volume into a different whole-bag purchase count.
Practical action: Read the mixed yield on the actual bag and replace the defaults before buying, then round up to whole bags.
Transferable rule: Product yield changes bag quantities only; it does not change the core-fill volume or the waste allowance.
Use when: Use for bagged product purchasing, not live prices, delivery minimums, site-mixed recipes, or structural material selection.

What does this estimate leave out?

The number above covers grout for standard two-core CMU cores, and nothing else. Ordering from it without checking these four boundaries is how a takeoff comes up short on delivery day.

Use the grout pattern and reinforcement details from the structural drawings. The calculator does not decide which cores need grout or design reinforcement.
Use Filled cores when the drawings provide an actual count. Spacing modes use a supplier planning benchmark for a standard two-core layout.
Use the manufacturer's core-volume table for 3-web, 4-web, architectural, or other nonstandard CMU shapes.
Bond beams, lintels, rebar, footings, slabs, and solid walls are outside this estimate.

Frequently asked questions

How much grout fills 100 8-inch concrete blocks?

About 1 cubic yard fills 100 fully grouted standard 8-inch two-core blocks (every core filled) before waste. At the default 0.60 cu ft yield that is about 45 80-lb bags, or about 2.2 blocks per bag. One cubic yard fills 65 standard 12-inch two-core blocks (about 1.54 cubic yards per 100). Add the waste allowance that fits the project and replace the default yield with the mixed volume printed on the bag.

How much concrete fills one 8x8x16 block?

For a fully grouted standard 8x8x16 CMU (every core filled), the calculator benchmark is 100 blocks per cubic yard, so one block is about 0.27 cubic feet (about 467 cubic inches) before waste. That is not the same as measuring the empty cores after subtracting shells and webs, which is how some tools arrive at about 550 cubic inches. Use the manufacturer's core-volume table when the block is not standard two-core CMU.

Should every CMU core be filled?

The project drawings should specify which cores are filled. Some walls use every cell, while others grout selected cells. This calculator estimates volume from the pattern you enter but does not choose the pattern or reinforcement.

Can I use concrete mix instead of masonry grout?

Use the material specified for the project. Masonry core-fill grout products state their ASTM C476 scope, while bagged concrete mixes have their own aggregate and yield specifications. Confirm the product with the plans, supplier, or project professional instead of using an unverified site recipe.

Does this calculator include bond beams, lintels, and rebar?

No. The result covers vertical cores represented by the selected mode and fill pattern. Bond beams, lintels, reinforcement, footings, slabs, solid walls, and other separate takeoff items are not included.

Continue the project estimate

Grout is one line on the material list. For the same standard CMU wall, jump to the calculator that answers the next question: how many blocks, how much mortar, or what the whole wall costs.