How many concrete blocks per square foot?

A standard 16x8 inch CMU with a 3/8-inch mortar joint covers about 0.89 sq ft, requiring roughly 1.125 blocks per square foot.

What is the standard concrete block size?

The most common CMU is the 8x8x16 inch block, nominally 8 inches tall, 8 inches wide, and 16 inches long.

How much mortar do I need for 100 blocks?

Approximately 0.9 cubic feet of mortar per 100 blocks, or about 2 bags of 60-pound pre-mixed mortar.

Should I include a waste factor?

Yes. A 5-10% waste factor is standard to account for cuts, corners, and breakage.

Can I use this calculator for retaining walls?

Yes for block quantity estimates, but retaining walls require structural engineering. Consult a licensed engineer.

Precise Calcs

Concrete Block Calculator – Estimate Blocks, Mortar & Cost

Calculate exactly how many concrete blocks you need for any wall or foundation.

This free concrete block calculator (CMU calculator) estimates the total number of concrete masonry units needed for your project, along with mortar bags and optional material cost. Enter your wall dimensions, choose your block size, and set a waste factor to account for cuts and breakage — a must-have block wall material estimate tool for contractors and DIYers alike.

Concrete Block Estimator

Wall Length

Decimal feet, e.g. 20.5 for 20’6″

Wall Height

e.g. 8.5 for 8’6″

Wall Dimension Units

Block Size (Length × Height)

Custom Block (inches): Length × Height

Mortar Joint Thickness

inches

Standard 3/8″ = 0.375. Range 0.25″–0.75″

Waste Factor

Recommended 5–10% for cuts & breakage

Price per Block (optional)

Leave blank to skip cost estimate

🧱 Enter dimensions & click
Calculate

Concrete Blocks Needed

—

including waste factor

Mortar Required

—

bags (60 lb each)

Wall area—

Block face (with mortar)—

Raw block count—

Waste added—

Your waste factor is already included. Keep a few spare blocks for future repairs.

How to Use This Concrete Block Calculator

Wall Dimensions

Enter your wall’s total length and height in feet, or toggle to meters using the unit selector.

Block Selection

Pick a standard CMU size (the 8×8×16 is most common) or input a custom size in inches.

Mortar Joints

Set joint thickness. Industry standard is 3/8″ (0.375). Thicker joints slightly reduce final block count.

Waste Allowance

Add a waste factor (5–10% recommended) to safely cover custom cuts, window openings, and breakage.

Project Costing

Optionally add the price per block to generate an instant, real-time material budget estimate.

Get Your Estimate

Hit Calculate. Your complete material counts, mortar bags, and cost breakdowns appear instantly.

Understanding Block Sizes and Mortar Joints

The most common CMU in the United States is the 8×8×16 block — 8 inches tall, 8 inches wide, and 16 inches long. Laid with a 3/8-inch mortar joint, each block occupies roughly 0.89 sq ft of wall face, meaning you need about 1.125 blocks per square foot. This masonry calculator adjusts automatically for your chosen joint size.

Block Size (L×H)	Face Area (with 3/8″ joint)	Blocks per sq ft	Common Use
16″ × 8″ (standard)	≈ 0.89 sq ft	≈ 1.125	Exterior walls, foundations, retaining walls
16″ × 4″ (half-high)	≈ 0.46 sq ft	≈ 2.18	Decorative walls, sill courses
16″ × 12″ (jumbo)	≈ 1.35 sq ft	≈ 0.74	Fast construction, heavy load-bearing

Frequently Asked Questions

A standard 16×8 inch CMU with a 3/8-inch mortar joint covers approximately 0.89 square feet. That means you need roughly 1.125 blocks per square foot — or about 113 blocks per 100 square feet before applying a waste factor. Use this concrete block estimator above to get an exact number for your wall dimensions.

The most widely used CMU in North America is the 8×8×16 inch block — nominally 8 inches tall, 8 inches wide (depth), and 16 inches long. Actual manufactured dimensions are slightly smaller (7-5/8″ × 7-5/8″ × 15-5/8″) to account for the mortar joint. This 8x8x16 block calculator uses nominal face dimensions for accuracy.

A common rule of thumb is approximately 0.9 cubic feet of mortar per 100 standard CMU blocks. One 60-pound pre-mixed mortar bag yields roughly 0.45 cubic feet when mixed, so plan on about 2 bags per 100 blocks. This mortar calculator for block wall projects applies this ratio automatically based on your final block count.

Yes — always. A 5–10% waste factor is standard practice for any block wall project. It accounts for blocks cut around windows, doors, and corners, plus accidental breakage during transport and installation. For simple straight walls use 5%; for complex layouts with many openings use 10%. This concrete block cost estimator applies your chosen percentage automatically.

Yes — this block wall calculator works for any rectangular CMU wall including retaining walls, garden walls, basement walls, and foundations. Enter total face length × height and the tool handles the rest. Note that retaining walls carry soil pressure loads requiring engineering reinforcement (rebar, grout fill) not covered by this estimator. Always consult a licensed structural engineer for load-bearing or retaining wall design.

Material Disclaimer: This concrete block estimator provides approximate quantities for planning and budgeting purposes only. Results do not account for footings, reinforcement, grout fill, or structural engineering requirements. Always verify quantities with your supplier before purchasing. Consult a licensed structural engineer for all load-bearing and retaining wall applications.

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Concrete Block Calculator – Estimate Blocks, Mortar & Cost

Calculate exactly how many concrete blocks you need for any wall or foundation.

How to Use This Concrete Block Calculator

Wall Dimensions

Block Selection

Mortar Joints

Waste Allowance

Project Costing

Get Your Estimate

Understanding Block Sizes and Mortar Joints

Frequently Asked Questions

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