Concrete Calculator: Wall (Stem Wall) Volume & Block Count

Estimate poured-concrete volume for stem walls and get a masonry block (CMU) count from wall area. Enter one or more wall runs, overall thickness, openings to subtract, and waste allowances. You’ll get wall area, concrete volume (m³, yd³, ft³), bag counts, and block quantities with waste. Notes, formulas, and FAQs are included.

Units Metric (m, mm) US Customary (ft, in)

Number of wall runs

1–12

Use separate runs for each straight wall length or height change.

Wall thickness (concrete)

Concrete waste

Covers spillage and dimensional variation (typ. 4–10%).

Block (CMU) type

Block waste

Extra for breakage and cuts (often 3–7%).

Wall runs

#	Length m	Height m

Subtract openings (optional)

Enter up to 4 openings (doors/windows). Their areas are subtracted from wall area for both concrete and blocks.

#	Width m	Height m
1
2
3
4

Results

Wall area

Gross: 0.000 m²

Openings: 0.000 m²

Net: 0.000 m²

Concrete volume

0.000 m³

0.000 yd³

0.00 ft³

With waste: 0.000 m³

Blocks (CMU)

Per net area: 0 pcs

With waste: 0 pcs

Face area per block: —

Approximate bag counts (for concrete, with waste)

US bag sizes (QUIKRETE® yield)

40 lb bag00.30 ft³ per bag

50 lb bag00.375 ft³ per bag

60 lb bag00.45 ft³ per bag

80 lb bag00.60 ft³ per bag

90 lb bag00.675 ft³ per bag

Yields per bag from QUIKRETE data sheet. Actual yield varies with placement and compaction. Source

How to use this wall calculator

Select metric or US units.
Enter the number of wall runs, then fill in each run’s length and height.
Set the wall thickness (for poured concrete volume).
Optional: enter up to four openings to subtract from area.
Choose the CMU type (or custom face size) for block counting and set waste percentages.
Read wall area, concrete volume (with bag counts), and block totals (with waste). Round up for ordering.

Formulas and assumptions

Gross wall area: A_gross = Σ (L × H).
Openings area: A_open = Σ (W × H).
Net wall area: A_net = max(A_gross − A_open, 0).
Concrete volume: V = A_net × T (thickness converted to meters), then with waste V_w = V × (1 + w%).
Blocks: N = A_net / A_face, where A_face is the nominal block face area including typical joints (e.g., 8×16 in ≈ 0.8889 ft² per block, ~1.125 blocks/ft²).
Waste (blocks): N_w = N × (1 + w%).
Scope: Volume and counts only—does not size reinforcement, bond beams, lintels, grout, or mortar quantities.

References

Typical concrete waste allowance ~4–10%: NRMCA Concrete In Practice CIP 8, CIP 31.
US nominal CMU sizes & ASTM C90 specification: NCMA/ICPI resources and TEK Guides (NCMA), ASTM C90 (Standard Spec).
Blocks per square foot (8×16 in ≈ 1.125 blocks/ft²) derives from nominal face area 0.8889 ft² with 3/8 in joints; see CMU size tables (e.g., industry charts).

FAQs

Does thickness affect block count?

No. Block count uses wall face area. Thickness affects poured-concrete volume only.

What joint size is assumed for CMU?

Nominal sizes generally assume ~10 mm (3/8 in) mortar joints. If your block system differs, use the custom face size option.

Are lintels and bond beams included?

No. This calculator treats the wall as uniform. Calculate lintels/bond beams separately or ask for a version with zones.