Concrete Block Calculator
Calculate the number of concrete blocks (CMUs), mortar bags, and material cost for your wall or foundation project. Supports standard block sizes, custom dimensions, and accounts for openings like doors and windows.
What Is a Concrete Block Calculator?
A concrete block calculator (or CMU calculator) is a tool that estimates the number of concrete masonry units (CMUs) needed for a wall or foundation project. It accounts for block size, mortar joints, wall dimensions, and subtracts openings like doors and windows.
This calculator supports standard block sizes (8×16, 8×12, 8×8, 6×16, 4×16) and custom dimensions. It also estimates the number of mortar bags required and calculates the total material cost — making it an essential tool for contractors, builders, and DIYers.
How Does the Concrete Block Calculator Work?
The calculator uses the following formulas:
Wall Area = Wall Length × Wall Height
Net Wall Area = Wall Area − Total Opening Area
Block Area (with mortar) = (Block Length + Joint) × (Block Height + Joint)
Blocks per Square Foot = 144 / Block Area (in inches)
Total Blocks = Net Wall Area (sq ft) × Blocks per Square Foot
Mortar Bags = (Total Blocks / 100) × Mortar Bags per 100 Blocks
A waste factor (default 5-10%) is applied to account for cuts, breakage, and miscalculations.
Why Use This Concrete Block Calculator?
- Accurate Estimates: Accounts for mortar joints and block dimensions.
- Opening Subtraction: Subtract doors, windows, and other openings.
- Waste Factor: Add extra blocks for cuts and breakage.
- Mortar & Cost: Estimate mortar bags and total project cost.
- Free & Private: No registration, no data storage.
❓ Concrete Block Calculator FAQ
What is a concrete block (CMU)?
A concrete masonry unit (CMU) is a rectangular block used in construction. Standard sizes include 8×8×16 inches (nominal) and are available in various thicknesses.
How many concrete blocks do I need for a wall?
Multiply the wall area by the number of blocks per square foot. A standard 8×16 block with a 3/8″ mortar joint covers about 1.125 sq ft per block (0.89 blocks per sq ft).
What is the actual size of a concrete block?
A standard 8×16 block measures 7-5/8″ × 15-5/8″ to allow for a 3/8″ mortar joint. The nominal size includes the mortar joint.
How much mortar do I need for concrete blocks?
A standard 80 lb bag of mortar mix typically lays about 30-35 blocks. Plan on about 3 bags of mortar per 100 blocks.
What is a waste factor and why is it important?
The waste factor (typically 5-10%) accounts for blocks broken during delivery or installation, cuts needed at corners and openings, and minor miscalculations.
How do I subtract openings like doors and windows?
Enable the "Add Openings" toggle and enter the width and height of each opening. The calculator subtracts the opening area from the total wall area.
What is the difference between nominal and actual block size?
Nominal size includes the mortar joint (e.g., 8×16). Actual size is 3/8″ smaller to allow for the joint (e.g., 7-5/8″ × 15-5/8″).
How do I calculate blocks per square foot?
Divide 144 sq in (1 sq ft) by the area of one block including the mortar joint. For a standard 8×16 block with a 3/8″ joint, this is approximately 0.89 blocks per sq ft.
What is the most common concrete block size?
The most common nominal size is 8″ × 8″ × 16″ (200 mm × 200 mm × 400 mm).
How do I estimate the cost of a block wall?
Multiply the number of blocks by the price per block, and add the cost of mortar bags. This calculator includes optional price fields for both.
What is the difference between concrete block and cinder block?
Cinder blocks are a type of concrete block made with coal ash (cinders) as aggregate. The terms are often used interchangeably, though cinder blocks are typically lighter.
Can I use this calculator for foundation walls?
Yes. Enter the wall length and height, select your block size, and add any openings. The calculator will estimate the blocks and mortar needed.