About Block Wall Grout Fill Calculator (NCMA TEK 4-2A)
The block wall grout fill calculator answers the follow-up question every hollow-CMU wall raises after the block count: how much grout do the cores need? Enter the net wall area (directly or as length × height), pick the block width and the vertical grout spacing — every cell, or reinforced cores at 16, 24, 32, 40, or 48 inches on center — and the tool reads the grout volume from the National Concrete Masonry Association's published estimating table, then converts it to cubic yards for a ready-mix order and to whole 80 lb premix bags at a datasheet-seeded yield you can edit.
This is the core-fill companion to the brick & block mortar calculator: that tool counts units and bedding mortar, while this one fills the vertical cells with grout per the NCMA tables. The table values assume conventional two-core units and already include about 3% waste; the extra-waste field is for pumping losses, cleanouts, and small pours where a larger fraction ends up outside the wall.
How It Works
- Enter the net wall area in square feet, or switch to length × height entry. Subtract openings — grout quantity follows the actual grouted wall face.
- Pick the nominal block width: 6, 8, 10, or 12 inches. The NCMA table excludes 4-inch units because their small cells cannot be grouted and consolidated reliably.
- Pick the grout spacing. "All cells" grouts every core (the 8 in on-center module of two-core block in running bond); the spaced options grout only the reinforced cores at 16 to 48 inches on center. Bond-beam courses are extra — add their volume separately (see the FAQ).
- The tool multiplies your area by the table's cubic feet per 100 ft² of wall, applies any extra waste you enter on top of the built-in 3%, and reports cubic feet and cubic yards — the yardage is what a ready-mix supplier quotes against.
- For bagged grout, the bag count divides the pooled volume by the per-bag yield (seeded at 0.65 ft³ per 80 lb bag from the QUIKRETE Core-Fill Grout data sheet — edit it to match your product) and rounds up once at the end, so partial bags carry across the pour instead of inflating every line.
Worked Example
A 20 ft long × 5 ft tall stem wall of 8-inch block, reinforced and grouted at 16 inches on center. Wall area = 20 × 5 = 100 ft². The NCMA table gives 18.1 ft³ of grout per 100 ft² for an 8-inch wall at 16 in o.c., so the pour needs 18.1 ft³ = 0.67 yd³. In 80 lb premix bags at the datasheet yield of 0.65 ft³ per bag, 18.1 ÷ 0.65 = 27.8 → 28 bags. Fully grouting the same wall (all cells) would take 36.1 ft³ — exactly the doubling you would expect going from every-16-inch cores to every-8-inch cores.
Formulas
- Grout volume from the NCMA table
V = (A / 100) × v₁₀₀ × (1 + w/100)- Yardage and bag count
yd³ = V / 27; bags = ⌈V / y⌉
Standards & References
- NCMA TEK 4-2A, Estimating Concrete Masonry Materials (2004), Table 3 — grout volume per 100 ft² of hollow single-wythe wall by width and grout spacing (two-core units, 3% waste included); Table 4 footnote gives 0.66 ft³ per 80 lb preblended-grout bag
- NCMA/CMHA TEK 9-4A, Grout for Concrete Masonry — the grout material specification (ASTM C476 proportions, slump, admixtures) this estimating tool assumes
- QUIKRETE Core-Fill Grout – Coarse, product no. 1585-07 data sheet (rev. Nov 2024) — 0.65 ft³ (18.4 L) yield per 80 lb bag, ASTM C476 compliance, 8–11 in slump
Frequently Asked Questions
How much grout do I need to fill an 8-inch block wall?
Fully grouted, an 8-inch hollow CMU wall takes about 36.1 ft³ of grout per 100 ft² of wall — roughly 1.34 cubic yards — per the NCMA estimating table. Grouting only reinforced cores cuts that roughly in proportion to the spacing: 18.1 ft³ at 16 in o.c., 12.1 ft³ at 24 in o.c., and 6.1 ft³ at 48 in o.c. per 100 ft².
How many bags of core-fill grout does it take per block?
The QUIKRETE Core-Fill Grout data sheet rates one 80 lb bag (0.65 ft³) to fill the cores of about 3 standard 8×8×16 blocks. For whole walls the per-area table is more reliable than per-block counting, because webs, mortar protrusions, and waste vary — that is what this calculator uses.
Does the calculator include bond beams?
No — the table covers vertical-core grouting only. Add bond-beam volume separately: NCMA TEK 4-2A Table 5 rates an 80 lb preblended bag at about 2.7 lineal feet of 6-inch, 2.0 ft of 8-inch, or 1.6 ft of 12-inch bond beam. A typical single bond-beam course adds one course-height band of fully grouted wall to the takeoff.
Should I order ready-mix or use bagged grout?
The usual break-even is around half a cubic yard to a yard: below it, bags mixed on site are cheaper and avoid a short-load fee; above it, ready-mix conforming to ASTM C476 is faster and more consistent for pumping. This tool reports both cubic yards and bag counts so you can price both routes.
Why is 4-inch block missing from the width picker?
NCMA excludes 4-inch units from its grout-volume table and recommends against grouting them at all: the cells are too small to place and consolidate grout adequately. The table (and this tool) covers 6, 8, 10, and 12-inch hollow two-core units.
Is waste already included in the numbers?
The NCMA table values include about 3% waste. The extra-waste field is additive, for conditions the table cannot know: pumping line losses, cleanout spillage, highly absorptive lightweight units, or small pours where the fixed losses loom larger. Waste is applied to the pooled volume before the single round-up to whole bags.