Reference

Concrete block sizes and weights

A block is sold under a name it does not measure. An 8×8×16 is 7⁵⁄₈ inches every way it is named for, and the missing three eighths is the mortar joint that makes the module work. Cinder block, cement block, CMU and concrete masonry unit all name the same product. Here is every size a yard stocks, what each one weighs, and where the two numbers matter.

CMU dimensions: nominal and actual

Nominal size is the module — the size the block occupies once it is laid, joint included. Actual size is what you measure with a tape. Every standard unit is 3⁄8 in under its nominal size in each direction that carries a joint.

Nominal	Actual (in)	Actual (mm)	Face area	Per 100 sq ft
4 × 8 × 16 in	3⅝ × 7⅝ × 15⅝	92 × 194 × 397	0.889 sq ft	112.5 blocks
6 × 8 × 16 in	5⅝ × 7⅝ × 15⅝	143 × 194 × 397	0.889 sq ft	112.5 blocks
8 × 8 × 16 in	7⅝ × 7⅝ × 15⅝	194 × 194 × 397	0.889 sq ft	112.5 blocks
10 × 8 × 16 in	9⅝ × 7⅝ × 15⅝	244 × 194 × 397	0.889 sq ft	112.5 blocks
12 × 8 × 16 in	11⅝ × 7⅝ × 15⅝	295 × 194 × 397	0.889 sq ft	112.5 blocks

Only the width changes across the range. Every standard unit presents the same 8 × 16 in face, so the block count for a wall is identical whether it is 4 inch or 12 inch — 1.125 blocks per square foot, 112.5 per hundred. What changes with width is the weight, the grout volume and what the wall can carry.

Concrete block weight by size

Weight depends on the aggregate, not the shape. Normal-weight units use sand and gravel at roughly 125 lb per cubic foot; lightweight units use expanded shale or slag and come out about 25 to 30 percent lighter for the same size. Both are sold as the same nominal block.

Nominal size	Normal weight	Lightweight	Per pallet
4 × 8 × 16 in	26–28 lb	18–20 lb	120
6 × 8 × 16 in	30–32 lb	22–24 lb	108
8 × 8 × 16 in	36–38 lb	26–28 lb	90
10 × 8 × 16 in	44–46 lb	32–34 lb	72
12 × 8 × 16 in	50–55 lb	36–40 lb	60

Pallet counts vary by yard — check before ordering by the pallet rather than the block. A full pallet of 8 inch normal-weight units runs about 3 400 lb, which is more than most half-ton pickups should carry and the reason blocks usually arrive on a boom truck.

Course heights and coursing

Every course adds exactly 8 inches — the block plus its bed joint. That makes coursing easy to plan and easy to get wrong: a wall height that is not a multiple of 8 inches ends in a cut course, and cutting block is slow.

Courses	Height	Common use
3	2 ft 0 in	Garden wall, planter
6	4 ft 0 in	Low retaining, crawl space
9	6 ft 0 in	Privacy wall
12	8 ft 0 in	Full storey, garage wall
16	10 ft 8 in	Tall shop or basement wall

Why cinder block and concrete block are the same thing

A true cinder block used coal cinders as its aggregate, and coal ash stopped being a by-product worth collecting decades ago. What a store sells today as cinder block, cement block, CMU or concrete masonry unit is one product: a hollow concrete unit with two cells. The names survive regionally, and a supplier will know what you mean whichever one you use.

The distinction that does still matter is normal weight against lightweight, because that is a 10 lb difference on every unit you lift. On a 200 block wall it is a ton of difference over the day.

Count the blocks for your wall →

Building in brick instead? Brick dimensions and course heights covers the same ground for every named brick format. For the steel that runs through grouted cells, see rebar sizes and weights.

Put these figures to work

These are the dimensions every masonry calculator on the site runs on. Each tool applies them to one kind of wall.