Concrete Block Fill Calculator
Grout volume, cubic yards, and bag count for filling CMU walls, with the source shown next to every number.
Order this much grout · CMHA method
2.14 yd³
57.76 ft³ · 97 × 80 lb bags
C90 minimum-thickness geometry
2.12 yd³57.17 ft³
Bare cell volume at ASTM C90 minimum face shell and web, plus your waste %. Carries no CMHA field allowance.
These two numbers land close together, and that is the point. The geometric figure uses ASTM C90 minimum face shell (1.25 in) and web (0.75 in) thicknesses, which produce the largest cell volume the standard allows: 0.302 ft³ per 8 in block. CMHA Table 2 reports 0.321 ft³ per block once field waste and overfill are included. Real units are usually made thicker than C90 minimums, so a wall built from typical block needs less than either figure. Order to the CMHA number. Why the two numbers differ.
Bond beam grout: 0.00 ft³ (0.00 yd³)
Added on top of both figures. CMHA Table 2 excludes bond beams and other horizontal grouted courses, so this is computed separately.
Inputs used
- Block count
- 180
- Wall area
- 160 ft²
- Blocks / ft²
- 1.125
How this calculator works
Grout volume comes from CMHA TEK 09-04A, Table 2, the masonry industry’s grout estimation table. The table is indexed by two things: the wall’s nominal thickness (6, 8, 10, or 12 in) and the grout spacing: how many cells you actually fill. It gives a volume in cubic feet per 100 ft² of wall area, already including a waste allowance for real-world overfill.
The calculator looks up that figure for your wall thickness and spacing, scales it to your actual wall area (from wall length × height, or from a block count converted at 1.125 blocks per ft²), and then adds bond-beam grout separately. Bond beams are horizontal grouted courses that Table 2 explicitly excludes, so their volume is computed from the block geometry and added on top. Finally the total is divided by the yield of your chosen bag to give a bag count.
Worked example
A 20 ft × 8 ft, 8 in wall grouted at 32 in o.c. with 1 bond beam course (0% extra waste, to keep the arithmetic clean: the table already carries its own cell-grout allowance):
- Wall area: 20 ft × 8 ft = 160 ft².
- Table lookup: CMHA Table 2 at 8 in, 32 in o.c. = 9.1 ft³ per 100 ft².
- Scale to area: 9.1 × (160 ÷ 100) = 14.56 ft³ of cell grout.
- Bond beam: 1 course × 20 ft × (7.625 in ÷ 12) course height × (5.125 in ÷ 12) clear width ≈ 5.43 ft³.
- Total: 14.56 + 5.43 = 19.99 ft³ ≈ 0.74 yd³.
- Bag conversion: 19.99 ft³ ÷ 0.60 ft³ per 80 lb bag = 33.3 → 34 bags.
Grout spacing changes the answer by 5.9x
At 8 in wall thickness, solid grouting (all cells) takes 36.1 ft³ per 100 ft², while 48 in o.c. takes only 6.1 ft³: a 5.9× spread. Partially grouted walls fill a reinforced cell only every few feet (with the cells between left hollow), so the grout quantity drops fast as spacing widens. Choosing “all cells” when your engineer specified 48 in o.c. overstates grout by nearly six times: a common and expensive error.
Grout is not concrete
Masonry grout is a high-slump mix. Per ASTM C476 and TMS 602, grout is placed at an 8 to 11 in slump so it flows into the cells and consolidates around the reinforcing steel without leaving voids. Bagged concrete mix is far stiffer and is the wrong material for filling cells. It bridges and leaves gaps. Use a product formulated as masonry grout, and treat the bag counts here as an ordering estimate for a grout-consistency mix.
Structural safety notice
This tool provides estimates for planning only and is not a substitute for a licensed structural or civil engineer. Do not use these results for load-bearing, safety-critical, or code-compliance decisions.