Concrete Block Calculator

Estimate the total number of cinder blocks (CMU) and mortar bags needed for your retaining wall, foundation, or masonry project.

Wall length feet Total linear length of the wall Please enter a positive number

Wall height feet Total height of the wall from base to top Please enter a positive number

Block size (face dimensions) Sizes are nominal and include a standard 3/8" mortar joint.

Calculation Results

Base blocks needed

— blocks

We strongly recommend ordering with a 5-10% waste buffer.

How to use this concrete block calculator

Enter your wall dimensions

Input the total length and total height of the wall you are building in feet.

Select your block size

Choose the face dimensions of your block. The thickness (depth) of the block (e.g., 4", 6", 8", 12") does not change the number of blocks needed for a single-layer wall.

Read your material list

The tool instantly calculates the exact number of blocks needed, the amount with a 5% waste buffer, and the estimated bags of mortar required.

Standard 8x8x16 Concrete Block & Mortar Estimation

Wall Length	Wall Height	Total Area	Blocks Needed	Mortar Bags (80lb)
10 ft	4 ft	40 sq ft	45 Blocks	2 Bags
10 ft	6 ft	60 sq ft	68 Blocks	3 Bags
10 ft	8 ft	80 sq ft	90 Blocks	3 Bags
10 ft	10 ft	100 sq ft	113 Blocks	4 Bags
10 ft	12 ft	120 sq ft	135 Blocks	5 Bags
20 ft	4 ft	80 sq ft	90 Blocks	3 Bags
20 ft	6 ft	120 sq ft	135 Blocks	5 Bags
20 ft	8 ft	160 sq ft	180 Blocks	6 Bags
20 ft	10 ft	200 sq ft	225 Blocks	7 Bags
20 ft	12 ft	240 sq ft	270 Blocks	9 Bags
30 ft	4 ft	120 sq ft	135 Blocks	5 Bags
30 ft	6 ft	180 sq ft	203 Blocks	7 Bags
30 ft	8 ft	240 sq ft	270 Blocks	9 Bags
30 ft	10 ft	300 sq ft	338 Blocks	11 Bags
30 ft	12 ft	360 sq ft	405 Blocks	13 Bags
40 ft	4 ft	160 sq ft	180 Blocks	6 Bags
40 ft	6 ft	240 sq ft	270 Blocks	9 Bags
40 ft	8 ft	320 sq ft	360 Blocks	11 Bags
40 ft	10 ft	400 sq ft	450 Blocks	14 Bags
40 ft	12 ft	480 sq ft	540 Blocks	17 Bags
50 ft	4 ft	200 sq ft	225 Blocks	7 Bags
50 ft	6 ft	300 sq ft	338 Blocks	11 Bags
50 ft	8 ft	400 sq ft	450 Blocks	14 Bags
50 ft	10 ft	500 sq ft	563 Blocks	17 Bags
50 ft	12 ft	600 sq ft	675 Blocks	21 Bags
80 ft	4 ft	320 sq ft	360 Blocks	11 Bags
80 ft	6 ft	480 sq ft	540 Blocks	17 Bags
80 ft	8 ft	640 sq ft	720 Blocks	22 Bags
80 ft	10 ft	800 sq ft	900 Blocks	27 Bags
80 ft	12 ft	960 sq ft	1080 Blocks	33 Bags
100 ft	4 ft	400 sq ft	450 Blocks	14 Bags
100 ft	6 ft	600 sq ft	675 Blocks	21 Bags
100 ft	8 ft	800 sq ft	900 Blocks	27 Bags
100 ft	10 ft	1000 sq ft	1125 Blocks	34 Bags
100 ft	12 ft	1200 sq ft	1350 Blocks	41 Bags

Frequently asked questions

How many concrete blocks do I need for a 10x10 wall?

A 10-foot by 10-foot wall has a surface area of 100 square feet. Using standard 16"x8" blocks, you will need exactly 113 blocks. With a standard 5% waste factor for cuts and breakages, you should order 119 blocks.

How do you calculate concrete blocks?

First, calculate the square footage of your wall (Length × Height). A standard 16"x8" block covers exactly 0.888 square feet of wall space when accounting for the 3/8" mortar joint. Simply multiply your wall's square footage by 1.125 to get the number of standard blocks needed.

How much mortar do I need per 100 blocks?

As a general industry rule of thumb, you will need approximately 3 bags of standard 80 lb mortar mix for every 100 standard concrete blocks (CMU) laid. This calculator automatically estimates the mortar bags required based on your block count.

Are cinder blocks and concrete blocks the same thing?

While people use the terms interchangeably, they are technically different. Concrete Masonry Units (CMUs) are made from steel, wood, and cement and are very heavy and strong. True "cinder blocks" are made with fly ash, making them lighter but less durable. Today, almost all load-bearing blocks sold are concrete blocks. Their dimensions are identical for calculation purposes.

Should I account for waste when ordering cinder blocks?

Yes. You should always add a 5% to 10% wastage factor to your final block count. This accounts for blocks that arrive cracked from the supplier, blocks broken during handling, and the half-blocks you will need to cut to stagger your vertical joints.

About this calculator

This concrete block calculator helps masons, contractors, and DIY builders estimate the number of Concrete Masonry Units (CMUs) required for a single-wythe wall. Whether you are building a foundation, a retaining wall, or a simple garden partition, this tool provides an exact material takeoff.

The math behind the tool relies on standard nominal block sizing:

Wall Area = Length (ft) × Height (ft)
Block Area (sq ft) = (Nominal Length (in) × Nominal Height (in)) ÷ 144
Blocks Needed = Wall Area ÷ Block Area
Mortar Bags (80 lb) = (Blocks Needed ÷ 100) × 3

A note on nominal vs. actual size: A standard 16" × 8" block is actually 15 5/8" × 7 5/8". The 3/8" difference is left intentionally for the mortar joint. Because of this, using the nominal 16" × 8" size in our formula automatically accounts for the space your mortar will take up, giving you a perfectly accurate block count.