Block Calculator
Calculate the number of concrete blocks (CMU) and mortar bags needed for a concrete block wall.
Formula & Explanation
The block calculator determines how many concrete blocks (CMU) and mortar bags are needed for a wall. **Wall Area** = height (ft) × length (ft) **Block Face Area** = block width (in) × block height (in) **Number of Blocks** = wall area (sq in) ÷ block face area (sq in), rounded up **Mortar Bags Estimate** = number of blocks ÷ 3.5 (standard ratio: ~3-4 blocks per 50-lb bag) Concrete blocks are larger than bricks, so fewer blocks are needed per wall, but each block requires more mortar per unit. The 3.5 blocks/bag ratio assumes standard 3/8" joints. Actual mortar yield varies with joint thickness, application method, and site conditions.
Assumptions
- •Standard US concrete block (CMU) dimensions: 8×8 inches (nominal face size) or 8×16 inches
- •Common block sizes: 4×8, 6×8, 8×8, 8×16, 12×8, 12×16 (width × height)
- •Standard mortar joint thickness: 3/8" (0.375")
- •One 50-lb bag of mortar yields approximately 3-4 blocks with standard 3/8" joints
- •Wall is assumed to be single wythe (single layer); double-wythe walls require doubling the block count
- •No deductions for windows, doors, or openings (calculate separately and subtract)
- •Mortar yield depends on joint thickness, technique, weather, and block porosity
- •Block types (solid, hollow, lightweight) may affect mortar consumption
Example Calculation
A 10×10 foot wall (100 sq ft) with 8×8 blocks requires approximately 180 blocks and 52 bags of 50-lb mortar, assuming standard 3/8" mortar joints.
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