Cinder Block Calculator

Calculate the exact number of cinder blocks 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.

Waste buffer % Extra blocks for cuts and breakages Please enter a valid percentage

Calculation Results

Cinder blocks to order

— blocks

Includes the requested waste buffer.

How to use this cinder 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.

Set your waste buffer

A standard 5% waste buffer accounts for blocks that break during transport or need to be cut.

Read your material list

The tool instantly calculates the exact number of cinder blocks to order and the estimated bags of mortar required.

Standard 8x8x16 Cinder Block Estimation (Includes 5% Waste)

Wall Length	Wall Height	Total Area	Cinder Blocks Needed
10 ft	4 ft	40 sq ft	48 Blocks
10 ft	6 ft	60 sq ft	71 Blocks
10 ft	8 ft	80 sq ft	95 Blocks
10 ft	10 ft	100 sq ft	119 Blocks
10 ft	12 ft	120 sq ft	142 Blocks
20 ft	4 ft	80 sq ft	95 Blocks
20 ft	6 ft	120 sq ft	142 Blocks
20 ft	8 ft	160 sq ft	189 Blocks
20 ft	10 ft	200 sq ft	237 Blocks
20 ft	12 ft	240 sq ft	284 Blocks
30 ft	4 ft	120 sq ft	142 Blocks
30 ft	6 ft	180 sq ft	213 Blocks
30 ft	8 ft	240 sq ft	284 Blocks
30 ft	10 ft	300 sq ft	355 Blocks
30 ft	12 ft	360 sq ft	426 Blocks
40 ft	4 ft	160 sq ft	189 Blocks
40 ft	6 ft	240 sq ft	284 Blocks
40 ft	8 ft	320 sq ft	378 Blocks
40 ft	10 ft	400 sq ft	473 Blocks
40 ft	12 ft	480 sq ft	567 Blocks
50 ft	4 ft	200 sq ft	237 Blocks
50 ft	6 ft	300 sq ft	355 Blocks
50 ft	8 ft	400 sq ft	473 Blocks
50 ft	10 ft	500 sq ft	591 Blocks
50 ft	12 ft	600 sq ft	709 Blocks

Frequently asked questions

How many cinder 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 cinder 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 for cinder blocks?

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

Are cinder blocks and concrete blocks the same thing?

Historically, cinder blocks were made with fly ash (cinders), making them lighter but less strong. Modern building codes usually require Concrete Masonry Units (CMUs) made with sand and gravel for load-bearing walls. Today, when people say "cinder block", they are usually buying a standard concrete block. Their sizes and dimensions are exactly the same.

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 cinder block calculator helps masons, contractors, and DIY builders estimate the number of 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
Total Blocks = Blocks Needed × (1 + (Waste % ÷ 100))
Mortar Bags (80 lb) = (Total Blocks ÷ 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.