CMU Block Calculator
Professional-grade concrete masonry unit calculator. Get block count, course count, mortar, grout, and rebar quantities for any CMU wall specification.
CMU Wall Calculator
// CMU Estimate
Understanding CMU Construction
CMU (Concrete Masonry Unit) walls are built in horizontal "courses" — each course is one block high. A standard 8" CMU block has a nominal height of 8 inches, so a wall 8 feet tall requires 12 courses (8 ft × 12 in/ft ÷ 8 in per course = 12 courses). The calculator accounts for this automatically, and uses the course count to determine exact block quantities per course.
For structural applications, vertical rebar runs through the hollow cores of the blocks from footing to top. These cores are then filled with grout to encapsulate the rebar and create a solid, reinforced assembly. The rebar spacing required depends on wall height, loads, and seismic zone — consult your structural engineer or local building code.
CMU Width Guide
| CMU Width | Wall Thickness | Typical R-Value | Best Application |
|---|---|---|---|
| 4" | 4" | R-0.8 | Interior partitions only |
| 6" | 6" | R-1.1 | Light exterior, fencing |
| 8" | 8" | R-1.1 | Standard exterior walls, garages |
| 10" | 10" | R-1.2 | High-load exterior, commercial |
| 12" | 12" | R-1.3 | Heavy load-bearing, retaining |
Note on R-value: Plain CMU has very low insulation value. For energy-code compliance, CMU walls typically require rigid foam insulation on the exterior or interior face. Check your local energy code requirements before specifying CMU for conditioned spaces.
Frequently Asked Questions
- What does CMU stand for in construction?CMU stands for Concrete Masonry Unit — the formal engineering term for concrete block. You'll see CMU on architectural drawings and structural specifications. At a hardware store, the same product is just called a concrete block or cinder block.
- How many courses of CMU per foot of wall height?Standard CMU is nominally 8 inches high (actual 7-5/8"), so you get 1.5 courses per foot of height. An 8-foot wall = 12 courses exactly. This clean number is why 8-foot and 16-foot wall heights are standard in CMU construction — they avoid cut blocks at the top.
- What mortar type should I use for CMU?Type S mortar is standard for exterior CMU walls, below-grade applications, and anywhere in contact with soil or water. Type N is acceptable for interior, above-grade, non-structural work. Never use Type M (too hard — it can crack blocks) for standard CMU.
- How do I calculate rebar for a CMU wall?Vertical rebar runs from the footing through the wall at specified spacings (typically 16", 24", 32", or 48" on center depending on engineering requirements). Each bar should extend the full height of the wall plus a lap splice into the footing (typically 40 bar diameters — 20" for #4 rebar). This calculator estimates bar count based on your selected spacing.