How much mortar do I need for concrete blocks?

As a rule of thumb, one 94-lb bag of masonry mortar covers about 25–35 standard (8×8×16) blocks. For a 100-block wall, plan for 3–4 bags. This varies based on joint thickness (typically ⅜ inch) and block type.

How heavy is a concrete block?

A standard 8×8×16 inch normal-weight concrete block weighs 28–40 lbs depending on the mix. Lightweight CMU blocks weigh 22–28 lbs. A pallet typically holds 90 blocks and weighs 2,500–3,500 lbs.

Concrete Block Calculator – How Many Blocks Do I Need?

Enter your wall dimensions and block size. The calculator accounts for mortar joints automatically.

Wall length (ft)

Wall height (ft)

Block size (nominal)

Waste factor (%)

Block price each ($) (optional)

Block Sizes

Nominal	Actual
8×8×16	7⅝×7⅝×15⅝
4×8×16	3⅝×7⅝×15⅝
6×8×16	5⅝×7⅝×15⅝
12×8×16	11⅝×7⅝×15⅝

Nominal includes ⅜" mortar joint.

Concrete Block Calculator FAQ

Common questions about concrete block and CMU wall projects.

How many concrete blocks do I need per square foot?

A standard 8×8×16 inch block covers about 0.889 sq ft of wall face, so you need ~1.125 blocks per square foot (or about 113 blocks per 100 sq ft). Always add 5–10% for cuts and waste at corners and openings.

What is the standard size of a concrete block?

The most common CMU is the 8×8×16 inch block (nominal size). The actual dimensions are 7⅝ × 7⅝ × 15⅝ inches — the difference accounts for the ⅜-inch mortar joint. Other standard sizes include 4×8×16, 6×8×16, and 12×8×16 inches.

How many mortar bags do I need?

One 94-lb bag of masonry mortar covers roughly 25–35 standard blocks. Divide your total block count by 30 for a reasonable estimate. Pre-mixed mortar in bags is convenient for small projects; bulk mixing is more economical for large walls.

How heavy is a standard concrete block?

A normal-weight 8×8×16 CMU weighs 28–40 lbs. Lightweight CMU blocks weigh 22–28 lbs. A standard pallet holds 90 blocks and weighs about 2,500–3,500 lbs total.

What's the difference between a cinder block and a concrete block?

True cinder blocks were made with coal cinders and are mostly obsolete. Today, what people call "cinder blocks" are actually CMU (concrete masonry units) made with Portland cement and lightweight aggregate. Modern CMU blocks are stronger and more consistent. The terms are used interchangeably in common speech.