Block Wall Calculator — m to blocks, mortar, cost
How to use this calculator
Enter wall length and height, then choose the unit (m, cm, mm) from each dropdown and pick a block size and joint. The takeoff returns block count by course, mortar bags (general-purpose, 25 kg), wall area and weight — what a mason actually orders off the pallet.
Openings — subtract doors and windows by entering count and average size.
Grout — choose fill pattern: every course, every other, or bond beam only.
Vertical rebar — set bar diameter and cell spacing.
Horizontal rebar — bond beam blocks at course spacing intervals.
Cost — per block, per mortar bag, per rebar bar. Select your currency.
Labor — rate per m2, per block, or flat price.
Saved Calculations
| Time | Size | Blocks | Mortar | Area m2 | Material | Labor | Total |
|---|
How to Calculate CMU Blocks for a Wall (Metric)
A standard 390×190×190 mm hollow block on a 10 mm joint occupies a 400×200 mm module, so a square metre takes 12.5 units. The calculator works in coursing, not area: it counts whole blocks per course over the length and whole 200 mm courses over the height, then subtracts opening blocks rounded up to the cut. Use 5% waste for a clean running-bond wall, 10% with corners and returns, 15% for stack bond or heavy cutting. For a clay-brick wall instead, use the brick wall calculator (metric).
Formulas Used
Net area = length × height − openings. Blocks = ceil(length / module) × ceil(height / course) − opening blocks, then × (1 + waste). General-purpose mortar runs about 3 bags (25 kg) per m² of single-leaf wall at a 10 mm joint, scaled with joint thickness. Core grout is roughly 0.25 L per cell per filled course for a 190 mm unit; size grout volume separately with the mortar & grout calculator. Rebar lap splice = 40 bar diameters per EN 1996 (Eurocode 6).
Reinforcement and Related Work
Vertical B500B bars (8–20 mm) sit in grouted cells from 200 to 1200 mm on centre; horizontal bars (8–12 mm) run in bond-beam courses. For a reinforced concrete lintel or ring beam over openings, the concrete beam calculator sizes concrete and bar; segmental gravity walls are covered by the retaining wall calculator, and bagged footing concrete by the concrete bag calculator.
FAQ
Why round up per course? Blocks cannot be split on a modular grid, so a partial cell still consumes a full unit at a course end or against a jamb. Does the weight include grout and rebar? Yes — wall weight totals blocks, mortar, and any enabled grout and reinforcement, shown in kg or tonnes. Are estimates code-compliant? Quantities follow Eurocode 6 coursing and lap rules for planning only; a qualified engineer must design reinforcement for load-bearing or seismic walls.
On install day
In 2025 a standard 390×190×190 mm hollow block runs €1.50–€2.80 at the merchant and €6–€10 for a 25 kg bag of general-purpose mortar; installed labor sits at €35–€55/m² for a plain wall, €65–€95/m² with full grout and reinforcement. The single biggest takeoff mistake is forgetting corner & end blocks (square-end and bullnose units cost more and ship by the pallet), followed by under-ordering bond-beam blocks for the top course and any lintels — price these separately from field blocks. Per EN 1996, fully grout cells with vertical reinforcement, set the first course in a full bed of mortar (M5 / M10 designation), and tool joints concave for weather. For footings and bag concrete, see the mortar & grout calculator and the concrete bag calculator; veneer faces use the stone veneer calculator.
