How much grout do I need to fill 8-inch concrete block cores?

For a standard 8x8x16 CMU wall with all cells filled, you need 1.00 cubic yard of grout per 100 blocks, or 1.12 cubic yards per 100 square feet of wall area. For partial fill at 16" on center, this drops to 0.58 cu yd per 100 blocks. Source: Fairbanks Materials Inc. Grout Fill Chart.

How many 80-lb bags of grout fill 100 concrete blocks?

For full fill of a standard 8x8x16 CMU wall, 100 blocks requires 1.00 cubic yard (27 cubic feet) of grout. An 80-lb bag of QUIKRETE Core-Fill Grout Fine yields approximately 0.68 cubic feet, so you need about 40 bags per 100 blocks for full fill. Source: QUIKRETE Core-Fill Grout Fine data sheet #1585-08.

Does building code require all CMU cores to be filled?

No. IBC 2021 Chapter 21 does not require full core fill in all cases. Requirements depend on seismic design category, wall type, height, and applied loads. Retaining walls over 4 feet and walls in Seismic Design Categories C through F typically require full fill or reinforced cells per TMS 402-22. A licensed structural engineer determines fill requirements for your project.

What is the difference between fine and coarse grout for CMU fill?

Fine grout uses portland cement and graded sand only. It is required when the grout space is less than 2 inches clear in any direction (ASTM C476-20). Coarse grout adds pea gravel aggregate up to 3/8" and is used in wider cells. Both must achieve a minimum 2,000 psi compressive strength and 8-11" slump (ASTM C143) for proper core penetration. Source: ASTM C476-20; QUIKRETE data sheets.

Can I use regular concrete instead of grout to fill CMU cores?

No. Standard bagged concrete is too stiff and the aggregate too coarse to flow into block cores and around rebar. ASTM C476-20 specifies masonry grout with a minimum 8" slump. Using stiff concrete creates voids, reduces bond strength, and does not comply with IBC 2021 §2103.3. Always use purpose-formulated core-fill grout.

How do I calculate grout volume for a 12-inch CMU wall?

A 12x8x16 CMU fully filled requires approximately 1.54 cubic yards of grout per 100 blocks (1.73 cu yd per 100 sq ft). For partial fill at 16" on center, use 0.90 cu yd per 100 blocks. Source: Fairbanks Materials Inc. Grout Fill Chart; Clayton Company Grout and Insulation Fill Chart for CMU.

What waste factor should I add when ordering CMU grout?

Use a minimum 10% waste factor for bagged grout jobs. NCMA TEK 3-2A identifies 3-5% volume loss from consolidation shrinkage alone. Additional waste comes from spillage at lift tops, pump hose priming, and cleanout block removal. For pumped jobs with long hose runs, increase to 12-15%.

Concrete Block Fill Calculator — CMU Core Grout Volume & Bag Count

Find out exactly how much grout your CMU block wall needs. Enter your wall size or block count, pick your fill pattern, and get the volume in cubic yards, cubic feet, and bag count in under a second. Covers 6", 8", 10", and 12" standard two-cell blocks using verified data from the Fairbanks Materials grout fill chart and Clayton Company CMU fill reference.

✓ Free, No Signup Required ✓ Sources Cited ✓ No Data Stored or Transmitted ✓ ASTM C476 / IBC 2021 Referenced ✓ Reviewed by Site Author ✓ Last Reviewed: June 2026 ✓ Built by Muhammad Ramzan Babar, Physics Researcher (PhD Candidate)

🧱 CMU Core Fill Calculator

Step 1 — Choose Block Size

8×8×16 nominal (actual: 7-5/8"×7-5/8"×15-5/8") — cell void: 624 cu in/block — Standard residential and commercial walls

Step 2 — Enter Wall Size or Block Count

Wall Length *

Total length of one wall section

Wall Height *

Height from footer to top of wall

Number of Identical Walls

Use 4 for a four-sided foundation, etc.

Door Openings to Deduct

Door width × height in ft — deducted from wall area

Window Openings to Deduct

Window width × height in ft

Total Number of Blocks *

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Already have your block count? Enter it directly. Need to calculate blocks first? Use the concrete block calculator.

Step 3 — Fill Pattern

Full fill is required for most retaining walls over 4 ft and seismic zones per IBC 2021 Chapter 21. Verify with your structural engineer.

Step 4 — Grout Options

Grout Type Fine grout required when clear grout space is less than 2" (ASTM C476-20)

Grout Bag Size

Waste Factor (%)

10% recommended for spillage, consolidation shrinkage (NCMA TEK 3-2A), and lift joint waste

Grout Lift Height Affects pour schedule; does not change total volume

✓ No data stored · ✓ Results appear instantly below · ✓ Ctrl+Enter to calculate

How the Fill Volume Calculation Works

Block Count from Wall Area

Wall length × height gives gross square footage. After deducting openings, net area is divided by 0.889 sq ft per block face (1.125 blocks/sq ft) per ASTM C90-22.

Cell Void Volume

Each block has two hollow cells. The net void for a standard 8" block is approximately 624 cu in per block after subtracting face shell and web thicknesses (ASTM C90-22; InchCalculator dimensional analysis).

Fairbanks Fill Chart

Grout volume uses the industry-verified fill rates from Fairbanks Materials Inc.: 1.00 cu yd per 100 blocks for full fill of 8" CMU, adjusted for fill pattern and block size.

Bag Count & Cost

Total volume is divided by bag yield (80-lb ≈ 0.68 cu ft per QUIKRETE data sheet #1585-08), rounded up, then multiplied by your bag price plus delivery and labor if entered.

CMU Grout Fill Reference Chart

Cubic yards of grout per 100 blocks and per 100 square feet of wall, by block size and fill pattern. Data from the Fairbanks Materials Inc. Grout Fill Chart — the primary reference used by this calculator. Use this table to cross-check your results or to estimate by hand.

Block Size	Fill Pattern	Cu Yd / 100 Blocks	Cu Yd / 100 Sq Ft	Blocks / Cu Yd
6" Wall 6×8×16	All cells filled	0.83	0.93	120
	16" O.C.	0.49	0.55	205
	24" O.C.	0.37	0.42	270
	32" O.C.	0.31	0.35	320
8" Wall 8×8×16 Standard	All cells filled	1.00	1.12	100
	16" O.C.	0.58	0.65	171
	24" O.C.	0.44	0.50	225
	32" O.C.	0.38	0.43	267
10" Wall 10×8×16	All cells filled	1.23	1.30	80
	16" O.C.	0.75	0.82	137
	24" O.C.	0.56	0.63	180
	32" O.C.	0.47	0.53	214
12" Wall 12×8×16	All cells filled	1.54	1.73	65
	16" O.C.	0.90	1.01	111
	24" O.C.	0.68	0.76	146
	32" O.C.	0.57	0.64	174
Source: Fairbanks Materials Inc. Grout Fill Chart; Clayton Company Grout and Insulation Fill Chart for CMU. Standard two-cell block, 8" high × 16" long. Waste not included.

💡 When to Use This Table vs. the Calculator

This table gives you a fast sanity check. The calculator is more precise because it accounts for opening deductions, your specific waste factor, bag size yield, lift height, and cost. For projects over 5 cu yd, always use the calculator and add your actual waste percentage.

What CMU Core Fill Is and When It Is Required

Concrete masonry units (CMU) are manufactured with hollow cells running vertically through the block. Those cells reduce block weight and material cost, and they provide channels for vertical rebar and grout to create a reinforced masonry system. Filling those cells with grout transforms a hollow-cell wall into a composite structure with significantly higher shear, compressive, and lateral load capacity.

The grout bonds to the rebar and to the block face shells, creating a single structural unit. Without grout, rebar placed in hollow cells provides no tensile contribution because it has no bond to the masonry. This is why grout specification, slump, and placement method all matter as much as the volume you order.

Code-Driven Fill Requirements

IBC 2021 Chapter 21 and TMS 402-22 (the Masonry Design Standard) specify minimum reinforcement and grouting requirements by seismic design category (SDC), wall type, and applied loads. For retaining walls over 4 feet, foundation walls in SDC C through F, and any wall designed to resist lateral earth pressure, full grout fill is common practice and often required. For above-grade interior CMU partitions in SDC A or B, partial fill at rebar cells is typically sufficient.

Confirming fill requirements is not optional on permitted jobs. Your structural engineer's drawings will specify grouted cells, rebar size, and spacing. The calculator lets you estimate volume for any fill pattern — the engineer determines which pattern applies. For structural wall analysis, see the concrete load-bearing calculator or the retaining wall calculator.

Fine vs. Coarse Grout (ASTM C476-20)

Fine grout uses portland cement and graded sand only. It is required when the grout space in any direction is less than 2 inches clear of rebar. The TMS 602 Table 6 specifies minimum clear dimensions: 3/4" for fine grout in cells up to 5-ft-4-in pours. Coarse grout adds aggregate up to 3/8" and pours faster for larger volumes. Both types must reach a minimum 2,000 psi compressive strength and achieve an 8–11" slump (ASTM C143) to flow without bridging.

💡 Why Grout Slump Matters More Than Mix Strength

Under-slumped grout is the most common cause of voids in CMU cores. A grout that is too stiff will bridge across the cell before reaching the bottom course, leaving unfilled pockets around rebar that are invisible from the top. Always verify 8–11" slump at point of placement, not just at the mixer. Pre-wetting block cores in hot or dry weather slows absorption and helps maintain slump through deep cells (NCMA TEK 3-2A).

Three Sample Fill Calculations

Each example uses the same reference values as the calculator. Cross-check your results against these numbers.

Four-Sided Garage Foundation — 8" CMU, Full Fill

Wall: 40 ft × 8 ft tall, 4 walls

Openings: 1 door (3 ft × 7 ft)

Fill: All cells, 10% waste

Gross area = 40 × 8 × 4 = 1,280 sq ft

Door deduction = 3 × 7 = 21 sq ft

Net area = 1,259 sq ft

Blocks = ceil(1,259 × 1.125) = 1,417 blocks

Grout = 1,417 × 0.01 cu yd = 14.17 cu yd

With 10% waste = 15.59 cu yd (421 cu ft)

80-lb bags = ceil(421 ÷ 0.68) = 620 bags

At 620 bags, ready-mix grout delivery is worth pricing. Contact your local masonry supplier — bulk grout often runs $180–$260/cu yd delivered versus ~$8,000 in bagged material. Use the foundation wall calculator to cross-check your concrete quantities.

Garden Retaining Wall — 10" CMU, 16" O.C.

Wall: 25 ft × 5 ft tall, 1 wall

Fill: Rebar at 16" o.c., 10% waste

Note: Verify fill with engineer for walls over 4 ft

Net area = 25 × 5 = 125 sq ft

Blocks = ceil(125 × 1.125) = 141 blocks

Grout = 141 × 0.0075 cu yd = 1.06 cu yd

With 10% waste = 1.16 cu yd (31.4 cu ft)

80-lb bags = ceil(31.4 ÷ 0.68) = 47 bags

47 bags is a practical DIY pour in one session. Plan two low-lift pours of 24" each (two lifts for a 5 ft wall). For rebar spacing and quantity, use the rebar calculator.

Workshop Partition — 6" CMU, 24" O.C.

Wall: 30 ft × 10 ft, 1 wall

Openings: 1 door (3 ft × 7 ft), 2 windows (3 ft × 4 ft each)

Fill: 24" o.c. partial fill, 10% waste

Gross = 30 × 10 = 300 sq ft

Deductions = 21 + 24 = 45 sq ft

Net = 255 sq ft → 287 blocks

Grout = 287 × 0.0037 cu yd = 1.06 cu yd

With 10% waste = 1.17 cu yd (31.6 cu ft)

80-lb bags = ceil(31.6 ÷ 0.68) = 47 bags

At 24" o.c. on a 6" non-bearing partition, 47 bags is manageable in a single day. Fine grout is required for 6" cells per ASTM C476-20. Plan three pours of 40" each for a 10 ft wall using the low-lift method.

Five Errors That Lead to Wrong Grout Quantities

⚠ Error 1: Calculating on Gross Wall Area

A 40 ft × 8 ft wall with two 3 ft × 7 ft doors has 300 sq ft gross but only 258 sq ft of block area. Ordering grout for 300 sq ft wastes 42 sq ft worth of material — about 50 bags for an 8" full-fill wall. Always subtract rough opening area before calculating block count.

⚠ Error 2: Skipping the Waste Factor

Grout volume shrinks 3–5% during consolidation and curing (NCMA TEK 3-2A). Add spillage at lift tops, pump hose prime volume, and cleanout block removal, and you need a minimum 10% buffer. Ordering zero waste routinely results in stopping mid-wall to source more material from a hardware store at retail price.

⚠ Error 3: Using Nominal Block Volume Instead of Cell Void

A nominal 8" block has a gross volume of 8 × 8 × 16 = 1,024 cu in. The actual cell void is approximately 624 cu in (ASTM C90-22). Using nominal volume overestimates fill by 39%. This calculator uses verified cell void data from the Fairbanks fill chart, not nominal block dimensions.

⚠ Error 4: Substituting Mortar or Concrete for Grout

Mortar mix yields only 0.45 cu ft per 80-lb bag, not 0.68 cu ft. Worse, mortar is not formulated for core fill — it stiffens too fast and cannot flow around rebar. Using mortar in place of grout violates IBC 2021 §2103.3 and ASTM C476-20. Always verify "Core-Fill Grout" on the bag label, not "Mortar Mix" or "All-Purpose Mix."

⚠ Error 5: Ordering by Bags Without Checking Yield

Not all 80-lb bags yield the same volume. QUIKRETE Core-Fill Grout Fine (#1585-08) yields 0.68 cu ft per bag. The coarse version (#1585-07) yields 0.65 cu ft. A generic 80-lb concrete mix may yield only 0.45–0.50 cu ft. Always check the yield on the bag label and use that number, not a generic estimate.

Grouting Logistics, Lift Methods, and Code Requirements

Low-Lift vs. High-Lift Grouting

Low-lift grouting (IBC 2021 §2104.3) limits each pour to 24" for standard hollow-unit masonry before consolidation. It is the most common method for residential construction because no cleanout blocks are required below 24". Each lift must be consolidated by rodding or mechanical vibration before the next lift is placed. The mortar must set for at least 4 hours between pours.

High-lift grouting allows pours up to 5 ft 4 in (fine grout) or the full wall height (coarse grout with cleanouts). It requires cleanout openings at the base of each lift, mechanical vibration every 18" per IBC 2021 §2104.3.1, and patched cleanouts cured for at least 4 hours before grouting above them. High-lift is faster on tall walls but adds cost for cleanout block labor and patching. The concrete wall calculator can help you plan poured alternatives if you're weighing CMU vs. formed walls.

Ready-Mix vs. Bagged Grout

Bagged grout is cost-competitive below approximately 3 cubic yards. Above that threshold, flowable masonry grout from a ready-mix supplier is typically cheaper per cubic yard and eliminates on-site mixing labor. For foundation walls requiring 10+ cubic yards of full fill, request flowable masonry grout from your ready-mix supplier and verify it meets ASTM C476-20 and your structural drawings. For budget planning across the full project, the foundation cost calculator and project budget calculator let you model material vs. labor tradeoffs.

Rebar, Bond Beams, and Fill Interaction

Vertical rebar in CMU cores displaces a small volume of grout. For #4 rebar (0.196 sq in cross-section) in a 6 × 6.5-inch cell (39 sq in), displacement is less than 0.5% per bar — not significant in an estimate. However, horizontal bond beam blocks running the full wall length require grout in addition to vertical cell fill. Bond beam grout volume is typically 5–8% of your total wall fill and should be added to your order. Use the rebar grid calculator to plan your bar quantities alongside your grout order.

Temperature and Curing

QUIKRETE data sheets specify grout temperature must remain above 50°F for a minimum of 7 days after placement. In hot weather (above 90°F), protect grout from rapid moisture loss with wet burlap or polyethylene sheeting. In cold weather, heated enclosures or insulating blankets are required. Grout placed below 40°F ambient will not hydrate properly and may result in below-spec compressive strength (ACI 530).

💡 Pre-Pour Checklist for CMU Core Fill

Verify cells are clear of debris, broken web pieces, and mortar droppings
Check rebar is tied at correct spacing and proper cover is maintained
Dampen block cores in hot/dry conditions — no standing water (NCMA TEK 3-2A)
Test slump at placement point: 8–11" required (ASTM C143)
Have consolidation rod or vibrator on site before first bucket is poured
Know your lift height and have a stopwatch or clock for between-lift wait times
Order 10% more than your net calculation — running short mid-wall creates a cold joint

Frequently Asked Questions

How much grout does a standard 8" block wall need per 100 square feet?

For full fill of a standard 8×8×16 wall, you need 1.12 cubic yards per 100 sq ft of wall area (1.00 cu yd per 100 blocks). At 16" on center partial fill, this drops to 0.65 cu yd per 100 sq ft. These figures do not include a waste factor. Source: Fairbanks Materials Inc. Grout Fill Chart.

What is the yield of an 80-lb bag of QUIKRETE Core-Fill Grout?

An 80-lb bag of QUIKRETE Core-Fill Grout Fine (#1585-08) yields approximately 0.68 cubic feet. The coarse version (#1585-07) yields approximately 0.65 cubic feet. One 80-lb bag fills the cores of approximately 3 standard 8×8×16 blocks at full fill. Always check the yield on the specific bag you buy — yields vary slightly by water content. Source: QUIKRETE data sheets #1585-08 and #1585-07.

Is full core fill required by code for all CMU walls?

No. IBC 2021 Chapter 21 does not universally require full core fill. Fill requirements depend on seismic design category, wall type (bearing vs. non-bearing vs. retaining), applied loads, and local code amendments. Non-load-bearing interior partitions in Seismic Design Category A or B often require only rebar cells grouted. SDC C through F and retaining walls over 4 ft typically require full fill. A licensed structural engineer determines fill requirements for each wall on each project.

Can I pour an entire 8-foot wall in one continuous grout lift?

Not with the standard low-lift method. IBC 2021 §2104.3 limits low-lift grout pours to 24" before consolidation is required. For a full 8 ft wall using low-lift, you need at least 4 pours, each consolidated before the next. High-lift grouting allows larger pours but requires cleanout openings at the base of each lift and mechanical vibration every 18" (IBC 2021 §2104.3.1). Most residential masonry contractors use the 24" low-lift method to avoid cleanout block cost.

Why does my bag count not match what the bag coverage table says?

Discrepancies come from four sources: (1) using gross area instead of net area after opening deductions, (2) using the wrong bag yield — mortar mix yields 0.45 cu ft vs. core-fill grout at 0.68 cu ft per 80-lb bag, (3) not applying a waste factor, and (4) using nominal block volume instead of the actual cell void. This calculator accounts for all four. If your manual count is higher, check whether you are using the fill chart's "per 100 sq ft" column vs. the "per 100 blocks" column — they differ by approximately 12% for 8" CMU.

How do I calculate grout for bond beams in addition to vertical cores?

Bond beam blocks (U-shaped or open-top blocks) run horizontally and require grout along their entire length. To estimate bond beam grout separately: multiply bond beam length (ft) by the cross-section of the open channel (typically 6" wide × 6.5" deep = 39 sq in = 0.271 sq ft). Then multiply by rebar placement frequency (typically every 4 courses). Add this volume to your vertical core fill total. For a typical 8" wall with bond beams at every 4 courses, add approximately 5–8% to your vertical fill volume.

What is the cost difference between bagged grout and ready-mix for CMU fill?

For bagged grout at $12.50 per 80-lb bag (0.68 cu ft yield), the material cost is approximately $500–$520 per cubic yard before delivery. Ready-mix flowable masonry grout from a concrete supplier typically runs $180–$260 per cubic yard delivered (US national average, June 2026). Bagged grout is cost-effective for jobs under 3 cubic yards. Above that threshold, ready-mix saves money on material even after minimum load charges and delivery fees. The break-even point shifts based on your local ready-mix pricing and delivery minimums.

Sources & Calculation Methodology

All volume figures in this calculator are derived from verified industry fill charts and manufacturer data sheets. No figures are estimated or interpolated from unverified sources.

Fairbanks Materials Inc. Grout Fill Chart — Primary fill rate reference. Cubic yards per 100 blocks and per 100 sq ft for 6", 8", 10", and 12" CMU at all, 16", 24", and 32" o.c. fill patterns. fairbanksmaterials.com
Clayton Company Grout and Insulation Fill Chart for CMU — Secondary verification of fill rates for 10" and 12" block sizes. claytonco.com
QUIKRETE Core-Fill Grout Fine Data Sheet #1585-08 — Bag yield: 0.68 cu ft per 80-lb bag. Fills approximately 3 standard 8×8×16 blocks per bag. quikrete.com
QUIKRETE Core-Fill Grout Coarse Data Sheet #1585-07 — Bag yield: 0.65 cu ft per 80-lb bag. quikrete.com
ASTM C476-20 Standard Specification for Grout for Masonry — Fine and coarse grout classification, minimum 2,000 psi compressive strength, clear space requirements, proportioning by volume or strength. codes.iccsafe.org
IBC 2021 Chapter 21 — Masonry — §2103.3 grout material requirements; §2104.3 grout placement and lift heights; §2104.3.1 consolidation requirements; §2104.2.1 cleanout openings for high-lift grouting.
TMS 402-22 / TMS 602-22 (Masonry Design Standard) — Table 6 minimum clear grout space dimensions; seismic design category grouting requirements.
NCMA TEK 3-2A — Grouting Concrete Masonry Walls — Low-lift and high-lift procedures; consolidation method; 3–5% volume loss from consolidation shrinkage; prewetting guidance.
ASTM C90-22 Standard Specification for Loadbearing Concrete Masonry Units — Minimum face shell and web thicknesses; nominal vs. actual CMU dimensions. Used for cell void derivation and blocks-per-sq-ft calculation.
InchCalculator.com CMU Dimensional Analysis — Cell void dimensions: 312 cu in per cell for standard 8×8×16 block (624 cu in total per block). Used as dimensional cross-check against Fairbanks fill chart figures.

⚠ Disclaimer

This calculator provides estimates for planning purposes only. For permitted structural work, foundations, multi-story construction, retaining walls over 4 feet, and commercial projects, calculations must be verified by a licensed structural engineer per IBC 2021 §1604. ConcreteCalculate.com is not liable for structural decisions made from these estimates. Grout quantities depend on actual block void dimensions, mix water content, placement method, and waste — always add a minimum 10% to the calculated volume.

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