CMU block calculator

What block size does the preset use?

Standard preset assumes a 16 in × 8 in face (nominal 8×8×16 CMU). Actual manufactured sizes vary slightly—use Custom if your supplier publishes different dimensions.

Does this include half blocks and corners?

Not automatically. The count is a rectangular grid estimate. Add waste or order specialty units (corners, halves) separately per your layout.

How accurate is the mortar bag estimate?

It uses a common rule of thumb (~7 bags per 100 blocks for standard mortar). Joint thickness, block absorption, and mix type change usage—confirm with your mason.

Can I use this for brick walls?

The math works for any rectangular unit if you enter the correct face length, height, and joint. Brick counts are often done with brick-specific tools because courses and bonds differ.

This tool counts concrete masonry units (CMU) for rectangular wall runs using block face dimensions and mortar joint thickness.

• Pick a block preset (standard 8×8×16 in is most common in the U.S.) or enter custom face length and height.
• Enter wall length and height with the unit selector on each field.
• Add total door/window opening area, number of identical walls, and a waste percentage (5% typical for cuts and breakage).
• Results show blocks per course, number of courses, net blocks, order quantity with waste, and a rough mortar bag estimate.

• Foundation or stem walls before ordering CMU from the masonry yard.
• Garage or shed perimeter walls when converting linear feet and height to pallet counts.
• Interior partition walls—multiply by identical wall count for symmetric layouts.

1. 20 ft × 8 ft wall, standard 8×8×16 block, 3/8 in joint, no openings, 5% waste → about 189 blocks (~15 per course × 12 courses, rounded up with waste).
2. Same wall with 32 ft² of window/door openings → opening blocks deducted before waste is applied.