Concrete Block Wall Calculator
Enter the wall length and height, pick your block size and mortar joint, and get the total block count, mortar volume, and how many bags of cement and sand to buy - plus a to-scale wall diagram. Nothing uploaded.
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Full breakdown
Learn more: block counts, coursing, and mortar
Coursing runs on block height plus one joint
Each course is the block height plus one mortar joint, so a 215 mm block with a 10 mm joint gives a 225 mm course. The same applies sideways: a 440 mm block takes up 450 mm of wall once its joint is counted.
Both counts round up. A 3000 mm wall needs 6.67 blocks per course, so it plans for 7, and an 1800 mm height divides into exactly 8 courses of 225 mm. That is 56 full blocks before any bond, corner, or waste adjustment.
What the bond pattern does to the count
Running bond staggers alternate courses, so the calculator adds one cut block for every second course, four cuts across an eight-course wall. Stack bond lines the joints up vertically and adds none.
Flemish bond costs the most in cutting. It adds cuts worth 15% of the full-block count, so the same eight-course wall picks up 8 cut blocks instead of 4. Corners are counted separately, two blocks per corner per course, which puts 32 extra blocks on a two-corner version of that wall.
Waste applies last, to full and cut blocks together, and rounds up. 56 full plus 4 cuts at 10% waste comes to 66 blocks, or 63 at 5%.
What the mortar figures assume
The mix is 1:5 cement to sand by volume, with cement at 1500 kg/m³ and sand at 1600 kg/m³, sold in 25 kg bags. Every 100 litres of mortar works out to 25 kg of cement, exactly one bag, and about 133 kg of sand, which rounds up to 6 bags.
The litres figure covers joint geometry only: one bed joint per course across the wall length, plus the vertical joints between blocks in each course. It sizes each joint by its own thickness rather than by how deep the wall is, so it reads low on any wall thicker than the joint. Use it for the mix ratio and check the quantity against the coverage printed on the bag.
FAQ
How many blocks do I need for a 3 m by 1.8 m wall?
With 440 x 215 mm blocks, 10 mm joints, running bond and a 10% waste factor, 66. That is 7 blocks across and 8 courses, giving 56 full blocks plus 4 cuts for the stagger, rounded up after waste. At 5% waste it drops to 63.
What does the coursing note mean when it shows a remainder?
It divides the wall height by the course height without rounding up, then reports what is left over. A 2000 mm wall in 225 mm courses gives 8 whole courses and a 200 mm remainder, and the note suggests 1800 mm as the nearest height that finishes on a full course.
Does joint thickness change the block count?
It can, because the joint is part of both the course height and the block spacing. On a 3000 by 1800 mm wall the count stays at 7 by 8 with either a 10 mm or a 12 mm joint, but the mortar estimate rises from 3.4 to 4.9 litres.