Block Wall Calculator (Concrete CMU)
Estimate concrete blocks, mortar, grout, rebar, and material cost for a concrete block (CMU) wall. Supports US and metric units and both plain and reinforced walls.
Block Wall Material Estimator
Results
Enter your wall dimensions and click “Calculate materials” to see a full breakdown of blocks, mortar, grout, rebar, and cost.
How the block wall calculator works
This tool is designed for quick, practical estimates when planning a concrete block (CMU) wall for a garden, fence, garage, or small retaining wall. It does not replace structural design by an engineer, but it gives you realistic material quantities to discuss with suppliers or contractors.
1. Wall area and block count
The starting point is the wall face area:
Wall area = length × height
For a standard 8×8×16 in CMU (nominal size including mortar joint), the face area is approximately:
Block face area ≈ 1.125 ft² (0.104 m²)
The calculator uses:
Blocks (before waste) = wall area ÷ block face area
Blocks (with waste) = blocks × (1 + waste%)
2. Mortar volume
Mortar fills the horizontal and vertical joints between blocks. A common rule of thumb for standard 8×8×16 in blocks is:
- ≈ 0.8–1.0 ft³ of mortar per 100 blocks (≈ 0.023 m³ per 100 blocks)
The calculator uses a default factor and converts the volume into bags:
Mortar volume ≈ blocks × 0.008 ft³ (per block)
Mortar bags = mortar volume ÷ volume per bag
3. Grout and rebar (reinforced walls)
If you enable reinforcement, the calculator estimates:
- Vertical bars: based on spacing along the wall length and full wall height.
- Horizontal bars: based on spacing up the wall height and full wall length.
- Grout volume: approximated from the number of grouted cells and typical cell volume.
This gives a reasonable starting point for ordering materials, but final bar sizes and spacing must follow engineering design and local codes.
4. Cost estimation
If you enter unit prices, the calculator multiplies each quantity by its cost and sums them:
Total cost ≈ (blocks × cost/block) + (mortar bags × cost/bag) + (grout bags × cost/bag) + (rebar length × cost/ft)
Labor, equipment, footing concrete, drainage, and backfill are not included.
Practical tips for building a block wall
Plan for a proper footing
- Most block walls require a reinforced concrete footing below frost depth.
- Footing width is often 2× wall thickness, but always follow code and engineering guidance.
Use string lines and layout carefully
- Snap chalk lines and stretch string to keep courses straight and level.
- Dry-lay a course to check how blocks fit around corners and openings.
Drainage for retaining walls
- Provide gravel backfill and a perforated drain pipe behind retaining walls.
- Use filter fabric to keep soil out of the drainage layer.
When to call a professional
Hire a licensed engineer or experienced contractor if:
- The wall retains soil higher than about 3–4 ft (1–1.2 m).
- The wall supports a building, driveway, or other loads.
- You are in a seismic or high-wind region with strict code requirements.
FAQ: Block wall calculator
How many concrete blocks do I need per square foot?
For standard 8×8×16 in CMU, plan on about 1.125 blocks per square foot of wall area. The calculator uses this factor and adds your chosen waste percentage.
Can I use this for both retaining and non-retaining walls?
Yes, for material estimating. However, retaining walls and load-bearing walls must be structurally designed; this tool does not verify safety or code compliance.
Does the calculator include footing concrete?
No. It focuses on the block wall itself: blocks, mortar, grout, and rebar. Use a separate concrete or footing calculator to size and estimate the footing.
How accurate are the mortar and grout estimates?
They are based on typical consumption rates and are suitable for budgeting and ordering. Actual usage can vary with workmanship, joint thickness, block type, and waste, so always allow a margin.