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Concrete Block Calculator

Estimate the total number of concrete blocks, required mortar volume, and material cost for building CMU walls. Supports rectangular, triangular, and gable wall shapes.

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Select wall shape, enter dimensions, select block size, then calculate.

Wall Dimensions

Block Size & Mortar Joint

in
in
in
in
10%

Logistics & Cost Estimates (Optional)

lbs

Calculation Results

Awaiting Calculations

Fill in the wall layout shape, wall dimensions, block size preset, and click Calculate to view estimates.

Formula Details

Wall Area Formulas
Rectangle: A = L × H | Triangle: A = 0.5 × B × H | Gable Wall: A = (L × H_wall) + (0.5 × L × H_gable)

Calculates the total physical surface area of the wall layout based on its geometry.

Variables Explained
  • L / B
    Length / Base:Total horizontal length of the wall.
  • H / H_wall
    Height / Wall Height:Vertical height of the wall (or the eave height for a gable wall).
  • H_gable
    Gable Height:Peak ridge height of the triangular gable segment above the main wall.
Wall Volume Formula
Wall Volume = Wall Area × Wall Thickness

Determines the total three-dimensional space occupied by the concrete block wall.

Variables Explained
  • Wall Area
    Surface Area:The calculated face area of the wall.
  • Wall Thickness
    Thickness:Depth of the masonry wall (typically matches block width or depth).
Block Quantity Formula
Blocks Required = (Wall Volume / Nominal Block Volume) × (1 + Waste / 100)

Estimates the total number of concrete blocks required. Nominal Block Volume includes the actual block size plus the surrounding mortar joints.

Variables Explained
  • Nominal Volume
    Nominal Block Volume:Formula: (Block Length + Joint) × (Block Height + Joint) × Block Width
  • Waste
    Waste Allowance:Percentage added for chipped blocks, cuts, and site damage (typically 10%).
Mortar Volume Formula
Mortar Volume = (Wall Volume - Actual Block Volume) × (1 + Waste / 100)

Calculates the net mortar joint volume by subtracting the physical block volume from the total wall volume, then applies waste.

Variables Explained
  • Actual Block Volume
    Actual Block Volume:Formula: Raw Blocks Count × Block Length × Block Height × Block Width
  • Waste
    Mortar Waste Factor:Percentage added for mortar spills and mixing cleanup.

Calculation Example

Worked Example
Scenario

Calculate concrete blocks (16" × 8" × 8" nominal, actual 15.625" × 7.625" × 7.625") and mortar required for a residential basement wall measuring 40 feet long, 9 feet high, and 8 inches thick. Assume a 3/8" (0.375") mortar joint and a 10% waste percentage.

Calculation Steps
  1. 1.Calculate the total surface area of the rectangular wall.
    Area = 40 ft × 9 ft = 360 sq ft
  2. 2.Convert wall thickness to feet and compute wall volume.
    Thickness = 8 in = 8/12 ft = 0.667 ft | Volume = 360 sq ft × 0.667 ft = 240 cu ft
  3. 3.Determine nominal block dimensions by adding the 3/8" (0.375") mortar joint.
    Nominal Length = 15.625" + 0.375" = 16.0" (1.333 ft) | Nominal Height = 7.625" + 0.375" = 8.0" (0.667 ft) | Width = 7.625" (0.635 ft)
  4. 4.Compute nominal volume of one block unit and convert to cubic feet.
    Nominal Vol = 16.0" × 8.0" × 7.625" = 976 cu in | In cu ft = 976 / 1728 = 0.5648 cu ft
  5. 5.Calculate raw block count, apply 10% waste allowance, and round up.
    Raw Count = 240 cu ft / 0.5648 cu ft = 424.9 Blocks | Blocks Required = 424.9 × 1.10 = 467.4 => 468 Blocks
  6. 6.Compute wet mortar volume by subtracting physical block volume from total wall volume.
    Actual Block Vol = 424.9 × (15.625" × 7.625" × 7.625") = 424.9 × 908.43 cu in = 385,992 cu in => 223.38 cu ft | Mortar Volume = (240 cu ft - 223.38 cu ft) × 1.10 = 18.28 cu ft
Final Quantity Needed468 Blocks & 18.28 Cubic Feet of Mortar
Worked Example
Scenario

Calculate metric block quantities for a boundary garden wall measuring 20 meters long and 2 meters high, using standard metric blocks (400 × 200 × 150 mm nominal, actual 390 × 190 × 140 mm) with a 10 mm mortar joint and 10% waste factor. Wall thickness is 14 cm.

Calculation Steps
  1. 1.Compute the total surface area of the wall.
    Area = 20 m × 2 m = 40 sq m
  2. 2.Compute total wall volume using the actual thickness matching block width.
    Thickness = 14 cm = 0.14 m | Volume = 40 sq m × 0.14 m = 5.6 cu m
  3. 3.Determine nominal block dimensions by adding the 10 mm (0.01 m) mortar joint.
    Nominal Length = 390 + 10 = 400 mm (0.4 m) | Nominal Height = 190 + 10 = 200 mm (0.2 m) | Width = 140 mm (0.14 m)
  4. 4.Compute nominal volume of one block unit.
    Nominal Vol = 0.4 m × 0.2 m × 0.14 m = 0.0112 cu m
  5. 5.Calculate raw block count, apply 10% waste, and round up.
    Raw Count = 5.6 cu m / 0.0112 cu m = 500 Blocks | Blocks Required = 500 × 1.10 = 550 Blocks
  6. 6.Subtract physical block volume to estimate wet mortar requirements.
    Actual Block Vol = 500 × (0.39 m × 0.19 m × 0.14 m) = 5.187 cu m | Mortar Volume = (5.6 cu m - 5.187 cu m) × 1.10 = 0.454 cu m
Final Quantity Needed550 Blocks & 0.454 Cubic Meters of Mortar
Worked Example
Scenario

Estimate block and mortar quantities for a garage gable wall with a base length of 18 feet, wall height of 10 feet, and gable segment height of 4 feet. The wall thickness is 6 inches, using 16 × 8 × 6 in nominal blocks (actual 15.625" × 7.625" × 5.625") with a 3/8" mortar joint and 10% waste allowance.

Calculation Steps
  1. 1.Compute the total surface area of the gable wall (rectangular base + triangular gable).
    Area = (18 ft × 10 ft) + (0.5 × 18 ft × 4 ft) = 180 + 36 = 216 sq ft
  2. 2.Calculate the total wall volume.
    Thickness = 6 in = 6/12 ft = 0.5 ft | Volume = 216 sq ft × 0.5 ft = 108 cu ft
  3. 3.Determine nominal block dimensions by adding the 3/8" mortar joint.
    Nominal Length = 15.625" + 0.375" = 16.0" (1.333 ft) | Nominal Height = 7.625" + 0.375" = 8.0" (0.667 ft) | Width = 5.625" (0.469 ft)
  4. 4.Compute nominal volume of one block unit and convert to cubic feet.
    Nominal Vol = 16.0" × 8.0" × 5.625" = 720 cu in | In cu ft = 720 / 1728 = 0.4167 cu ft
  5. 5.Calculate raw block count, apply 10% waste, and round up.
    Raw Count = 108 cu ft / 0.4167 cu ft = 259.2 Blocks | Blocks Required = 259.2 × 1.10 = 285.12 => 286 Blocks
  6. 6.Subtract physical block volume to estimate wet mortar requirements.
    Actual Block Vol = 259.2 × (15.625" × 7.625" × 5.625") = 259.2 × 670.17 cu in = 173,707 cu in => 100.52 cu ft | Mortar Volume = (108 cu ft - 100.52 cu ft) × 1.10 = 8.23 cu ft
Final Quantity Needed286 Blocks & 8.23 Cubic Feet of Mortar

How to Use

Follow these simple steps to estimate the surface area, total block quantities, mortar requirements, and estimated material cost for your wall masonry layout:

  1. Choose Wall Shape: Select the shape of your wall (Rectangle, Triangle, or Gable Wall).
  2. Set Unit System: Toggle between Imperial (ft/in/yd) and Metric (m/cm/mm) at the top right of the estimator.
  3. Enter Wall Dimensions: Input the length, height (and gable ridge height if applicable), and total wall thickness.
  4. Select or Define Block Size: Choose a preset (e.g., 16 × 8 × 8 in, 400 × 200 × 200 mm) or select "Custom Size" to enter your specific block dimensions.
  5. Input Joint & Waste Factors: Enter the target mortar joint thickness (default is 3/8" or 10 mm) and adjust the waste slider (10% is recommended).
  6. Add Optional Values: Optionally enter the weight of a single block and the cost per block to receive shipping weight and overall materials cost estimates.
  7. Calculate: Click the Calculate button to compute results. Click Reset to clear the form at any time.

Frequently Asked Questions

How many concrete blocks do I need?
The number of concrete blocks is calculated by dividing your wall volume by the nominal volume of a single block (which includes the block's actual dimensions plus the mortar joint thickness). Toggling wall thickness and choosing different shapes directly scales the block count. A standard wall typically requires about 1.125 blocks per square foot for a 16" × 8" × 8" CMU size.
How much mortar is required?
Mortar volume is computed by taking the total volume of the wall structure and subtracting the actual physical volume occupied by all the blocks. Mortar generally accounts for 10% to 15% of a concrete block wall's volume. A 10% waste factor is added to cover site spills and mixing waste.
What block size should I choose?
A standard 16 × 8 × 8 in block is the typical choice for structural load-bearing walls and foundations. Thinner blocks like 16 × 8 × 6 in and 16 × 8 × 4 in are commonly used for garden borders, partitions, or veneers. Choose a preset from our list or select 'Custom Size' to input your own specifications.
Why should I include a waste percentage?
Blocks are frequently cut on-site to fit edges, corners, and window or door openings, which creates unusable remnants. Additionally, blocks can break or chip during transport. Adding a 10% waste allowance ensures you don't run out of blocks mid-build.
How accurate is the block estimate?
This calculator provides a precise geometric estimation. Real-world requirements can vary slightly depending on the masonry bond pattern and whether you subtract openings for windows and doors. Always buy a small buffer.
Can I use custom block dimensions?
Yes. By selecting 'Custom Size...' in the Block Size Preset dropdown, the length, height, and width fields become fully editable. You can enter any custom dimensions in inches (for imperial) or millimeters (for metric) to estimate your project.

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Disclaimer

Calculations are estimates based on the values you enter and standard engineering formulas. Results are intended for planning and estimation only. Always verify critical measurements, specifications, and local building requirements before purchasing materials or beginning construction.