Concrete Block (CMU) Calculator
Calculate CMU blocks, mortar, rebar, grout, and accessories for masonry wall construction. Supports standard, half-high, 12-inch, and 6-inch block sizes with openings, bond beams, and fill options.
Wall Dimensions
Block & Mortar
Openings to Subtract
Reinforcement
Typically every 4 ft of wall height
Accessories
Material Estimate
Gross Wall Area
320
sq ft
Openings Subtracted
45
sq ft
Net Wall Area
275
sq ft
Blocks & Mortar
CMU Blocks
318
8x8x16 (incl. 10% waste)
Mortar
28
80 lb bags
Sand for Mortar
4.0
tons
Reinforcement (#4 Rebar)
Vertical Bars
11
#4 @ 48" OC
Horizontal Rebar
80
linear ft (2 courses)
Total Rebar
168
linear ft
20 ft Rebar Sticks
9
#4 bars
Accessories
Bond Beam Blocks
60
knock-out / lintel blocks
Cap Blocks
30
solid top cap
Estimated Labor
2 days
1 mason + helper (~175 blocks/day)
Material Prices (for cost estimate)
Material Shopping List
Pro Tips
- Order full pallets (typically 90-110 blocks per pallet). Pricing per pallet is 10-20% better than individual block pricing. Plan storage area for delivery.
- Type S mortar for structural walls; Type N for non-load-bearing partitions; Type M for heavy-duty/below-grade. Using Type S where Type N is appropriate is fine but more expensive — using Type N where Type S is required is a code violation.
- Hollow wall over 6 feet? Most jurisdictions require some grouting for walls over 6 feet for stability. Verify with local building department before finalizing as hollow.
- Rebar order: Get rebar pre-cut at the supplier if possible — cutting #4 bar on site requires a rebar cutter or grinder and adds 0.5-1 hours per 20 sticks of cutting. Many suppliers will cut to length for $0.50-$1.00 per cut.
- Wall ties for veneer:Required by code when block wall has brick or stone veneer. Spaced 16" horizontal × 24" vertical max. Skipping wall ties = veneer separation within years.
- Check footing requirements.Block walls need proper concrete footing below frost line. Footing prep is typically NOT in your block bid — quote it separately if you're doing it, or coordinate with the concrete sub.
How to Use This Calculator
Enter your wall dimensions and the number of walls. Select the block size and mortar joint thickness. Subtract openings for doors and windows by entering counts and sizes, or enter custom square footage for irregular openings. Set bond beam courses (typically every 4 ft of wall height), choose your fill option (hollow, grouted solid, or partially grouted), and adjust rebar spacing. The calculator provides a complete materials list including blocks, mortar, rebar, grout, cap blocks, and wall ties.
Formula Used
Net Area = (Wall Length x Wall Height x Number of Walls) - Openings. Blocks = Net Area x 1.125 blocks/sq ft (for 8x8x16 with 3/8" joint) x (1 + Waste%). Mortar = Blocks x 8.5 bags/100. Grout per cell = 0.035 cf (8" block). Vertical Rebar = Wall Length / Spacing + 1 per wall. Horizontal Rebar = Bond Beam Courses x Wall Length.
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Disclaimer
This calculator is for estimation purposes only. Results may vary based on local conditions, materials, and building codes. Always consult a licensed professional before making decisions based on these calculations. MyContractorTools is not responsible for any errors or omissions.