Concrete Block Fill Calculator
Block fill grout = net wall area × grout per square foot for the block width × the share of cells grouted. A 40 × 8 ft wall of 8 in CMU grouted at 32 in on centre takes 28 ft³ (1.04 yd³), or 1.15 yd³ with 10% waste. For blocks and mortar too, use the Block Wall Calculator.
How it's calculated: Grout = net wall area × net grout per ft² (0.350 ft³ for fully grouted 8 in CMU, before waste) × fraction of cells grouted.
Result appears here
Fill in the fields and press Calculate.
Formula, calculation, assumptions and sources
Grout = Net wall area (ft²) × grout per ft² (by block size) × fraction of cells grouted
Full-grout rate (net, ft³ per ft² of wall): 6 in 0.249 · 8 in 0.350 · 10 in 0.456 · 12 in 0.572 (CMHA TEK 04-02A Table 3 ÷ 1.03)
Run the calculation to see each step with your own numbers.
A 40 ft × 8 ft wall of 8-in CMU, vertical cells at 32 in o.c., 10% waste.
Net area = 320 ft²; fraction grouted = 8 ÷ 32 = 0.25
Grout = 320 × 0.350 × 0.25 = 28 ft³ = 1.04 yd³ exact
+10%: order 1.15 yd³
- Standard hollow CMU with two cells per 16-in block.
- Grout-per-area figures are CMHA TEK 04-02A Table 3 values for the nominal block width with the table's 3% waste removed — a specific unit's cored area varies slightly.
- The waste allowance is the only waste added, so the order quantity is not double-counted.
- Face-shell mortar bedding. Fully mortared cross-webs reduce grout slightly.
- Does not include grout for a separate bond beam course — add that as extra wall area or a separate run.
- Do I grout every cell?
- Only where the structural drawings call for it. Many walls are grouted only at cells with vertical rebar (e.g. 32 or 48 in o.c.) plus bond beams. Full grouting is used for higher loads, retaining walls and below grade.
- Grout or concrete for filling cells?
- Masonry grout — a high-slump mix that flows into the cells and around the rebar without segregating. A stiff concrete mix will bridge and leave voids. For a very small job you can mix grout from bagged material.
- How much does the grout spacing change the quantity?
- Proportionally. Full grouting an 8-in wall takes about 0.350 ft³ per square foot of wall, before waste; grouting only the vertical cells at 48 in on centre uses about a sixth of that.
- How much grout do I need to fill concrete block?
- About 0.350 ft³ per square foot of wall to fully grout 8 in block, before waste. Grouting only the vertical cells at 32 in on centre uses a quarter of that — 28 ft³ for a 40 × 8 ft wall.
- How many bags of grout are in a cubic yard?
- About 45 bags of 80 lb grout mix per cubic yard, so the 1.15 yd³ example is roughly 52 bags.
Grout quantities
Net grout to fill every cell of a hollow two-core CMU wall: 0.249 / 0.350 / 0.456 / 0.572 ft³ per ft² of wall for 6 / 8 / 10 / 12 in units. These are CMHA TEK 04-02A Table 3's 25.6 / 36.1 / 47.0 / 58.9 ft³ per 100 ft² with the table's included 3% waste removed (÷ 1.03), so waste is added only once, by the waste allowance. Concrete Masonry & Hardscapes Association TEK 04-02A, 'Estimating Concrete Masonry Materials', Table 3.
About the Concrete Block Fill Calculator
The Concrete Block Fill Calculator estimates the grout needed to fill the hollow cells of a CMU wall — either every cell (full grouting, used for retaining walls, below-grade walls and higher loads) or just the vertical cells at a set spacing, which is how most reinforced walls are built. Enter the wall size, deduct openings, and pick the block width and the grout spacing your drawings call for. It returns grout only — block count, mortar and rebar are separate calculations.
What you enter
- Wall length
- Wall height
- Openings to deduct
- Block size (nominal width)
- Cells grouted
- Waste allowance — Default 10%. Adjust to your own allowance — the exact figure is always shown too.
What you get back
- Grout volume — Grout is often mixed from bags for a small job — 1 yd³ ≈ 45 × 80 lb bags of grout mix.
The formula, a worked example, the assumptions behind it and the sources are shown in full below the calculator.
Related calculators
- Concrete Block Calculator — Number of concrete masonry units (blocks) for a wall of a given area.
- Block Wall Calculator — Blocks, mortar and fill for a concrete block wall.
- Mortar Calculator — Mortar quantity for a brick or block wall.
- Rebar Calculator — Rebar quantity, spacing and lineal feet for a slab or footing grid.
Part of the Concrete calculators.