About

Accurate material estimation is critical in masonry to prevent costly shortages or excessive waste. This calculator determines the quantity of Concrete Masonry Units (CMU), commonly called cinder blocks, required for a wall or foundation. It accounts for the surface area of the wall relative to the face area of the chosen block size.

The tool includes a waste factor input to account for breakage during transport and cutting (typically 5-10%). It also estimates mortar requirements based on industry standards (~3 bags per 100 sq ft of standard block). Always verify structural load requirements with a local engineer before building foundations.

Formulas

The core calculation compares the total wall area to the block's face area (including mortar joints).

Area_wall = L × H

Count = Area_wallArea_block × (1 + Waste)

Standard mortar estimation assumes joint thickness of 38 inch.

Mortar_bags ≈ Count40

This ratio assumes standard 80lb premix bags.

Reference Data

Block Type	Nominal Size (in)	Actual Size (in)	Face Area (sq ft)	Blocks / 100 sq ft
Standard US	16 x 8 x 8	15.625 x 7.625 x 7.625	0.89	112.5
Half Block	8 x 8 x 8	7.625 x 7.625 x 7.625	0.44	225
Slim Block	16 x 8 x 4	15.625 x 7.625 x 3.625	0.89	112.5
Metric Std	390mm x 190mm	390 x 190 x 190 mm	0.074 m²	13.5 / m²

Frequently Asked Questions

Nominal size includes the expected mortar joint (usually 3/8 inch). A "16x8x8" block is actually smaller (approx 15 5/8 inches long) so that when laid with mortar, it occupies exactly 16 inches of space.

For straight walls, 5% is standard. For walls with many corners, windows, or specific bond patterns requiring cuts, calculate 10-15% waste.

This depends on the structural load. Foundation walls often require rebar and concrete fill (grout) in the vertical cores for strength. This calculator estimates blocks and mortar only, not core grout.

A standard pallet typically holds between 90 and 120 standard 8-inch blocks, depending on the supplier and block weight.