Cinder block dimensions are concrete block dimensions: under modern US codes and standards the two are functionally the same product, and ASTM C90 governs loadbearing units of either name. Standard cinder block dimensions are 8 by 8 by 16 inches nominal and 7 5/8 by 7 5/8 by 15 5/8 inches actual. The block is made 3/8 inch small so that its mortar joint brings it back to the 8-inch module, and the same 3/8 inch rule sets the length, height and width of every size. The two holes of the common unit take its grout and reinforcement, and a block’s weight follows the density of its concrete as well as its size, while metric blocks outside the United States follow the same logic with a 10 mm joint.
What Are Cinder Blocks?
Cinder blocks, also written cinderblocks, are concrete masonry units made of water, cement and aggregate, essentially the same product as concrete block in the view of the Concrete Masonry & Hardscapes Association, or CMHA, the US and Canadian trade association for concrete masonry. The meaning of the name is literal and dates from the early 20th century, when many producers, though not all, put cinders into block as a lighter alternative to stone aggregate, both coal-combustion by-products and volcanic cinders. Builders also call the unit concrete block, CMU or simply block, and a concrete block is a hollow or solid unit larger than a concrete brick.
Coal-combustion cinders were still used in block production as of 2014, and nothing about a block’s density shows whether it contains them; either way, every unit used in construction has to meet the building code’s minimum requirements. Fly ash, a byproduct of burning coal, is often included in concrete block. The 2009 International Building Code defines a concrete masonry unit as a building unit or block larger than 12 by 4 by 4 inches made of cement and suitable aggregates.
Francis J. Straub of New Kensington, Pennsylvania, filed for a patent on building blocks made with crushed coal cinders in November 1915 and was granted US patent 1,212,840 in January 1917. Concrete block was already a commercial product by then, thanks to Harmon Palmer’s block machine of 1900, and Straub licensed production of his cinder block into the 1930s; Pamela H. Simpson’s history of imitative building materials puts his licensees’ output at 70 million blocks a year by 1926.
What Are Cinder Block Dimensions?
Cinder block measurements, like those of other concrete masonry units (CMU), are given as nominal sizes, and a standard block is 8 by 8 by 16 inches nominal: 8 inches wide, 8 high and 16 long, which is how large it is in the wall once its joint is counted. The block itself is made 3/8 inch smaller in each direction, 7 5/8 by 7 5/8 by 15 5/8 inches, and the 3/8 inch mortar joint restores the nominal size. The typical face is 8 by 16 inches nominal, and the nominal width names the block, from 4 to 16 inches.
Two terms describe the block itself. The specified dimension is the size it is made to and the actual dimension is the size as measured, although layout guides and makers’ catalogs usually print the 7 5/8 inch figures as actual dimensions. ASTM C90 lets width, height and length stray no more than 1/8 inch, 3.2 mm, from the specified dimension, split-face and slumped units excepted, and structural design works from the minimum specified dimensions.
How Long Is a Cinder Block?
A cinder block is 15 5/8 inches long, 397 mm, or 16 inches nominal, so each block plus one 3/8 inch end joint advances a course by 16 inches. A run of blocks therefore measures 16 inches per block less a single 3/8 inch, because the last block in a course has no end joint, so a drawing of a block building has to take that 3/8 inch off the end of every run. A half block is 7 5/8 inches long, 8 inches nominal, one maker offers three-quarter units 11 5/8 inches long, and units with nominal lengths of 24 to 32 inches exist for architectural relief or faster construction.
How Tall Is a Cinder Block?
A cinder block is 7 5/8 inches tall, 194 mm, or 8 inches nominal, so each course adds 8 inches of wall height on the 8-inch vertical module. Twelve courses make an 8-foot wall, a typical US foundation wall, though custom-built houses can run to more courses. Half-high units 3 5/8 inches tall give 4-inch coursing where a wall needs it, and three courses of modular brick equal one 8-inch block course.
How Wide Is a Cinder Block?
A standard 8-inch cinder block is 7 5/8 inches wide, a dimension also called the unit’s thickness, and every width is made 3/8 inch under its nominal size: 4, 6, 8, 10, 12, 14 and 16 inch blocks are 3 5/8, 5 5/8, 7 5/8, 9 5/8, 11 5/8, 13 5/8 and 15 5/8 inches wide. A single-wythe wall is one block thick, so in that wall the block’s width is the wall’s thickness.
Metric Cinder Block Sizes
Metric cinder blocks follow a separate module. They are made 10 mm under a nominal 200 by 200 by 400 mm, so the metric unit is 190 by 190 by 390 mm, while the US 8-inch block converts to 194 by 194 by 397 mm, about 2 percent larger. The difference can cause complications when inch-pound units go into a structure designed on a 100 mm metric module, or metric units into an inch-pound design. Brampton Brick in Ontario sells a 20 cm standard block 190 mm wide for 10 mm joints, New Zealand’s Firth makes 90, 140 and 190 mm blocks on a 390 by 190 mm face, and Marshalls in the UK sells blocks 440 mm long, 215 mm high and 100 mm deep.
| Market | Face, height x length | Widths shown | Makers and bodies |
|---|---|---|---|
| United States | 7 5/8 x 15 5/8 in, 194 x 397 mm | 3 5/8 to 15 5/8 in | CMHA, County Materials |
| Metric module | 190 x 390 mm | 90, 140 and 190 mm at Firth, 10 to 30 cm nominal at Brampton Brick, its 20 cm block 190 mm wide | CMHA and Firth for the face, Brampton Brick for its widths |
| United Kingdom | 215 x 440 mm | 100, 140 and 215 mm | Marshalls, Tarmac, Hoddam |
Different Cinder Block Dimensions
The different cinder block dimensions are the nominal widths of 4, 6, 8, 10 and 12 inches, with 14 and 16 inch units also made, and most of them share the typical 8 by 16 inch nominal face. Each width is made in full and half lengths and in shapes for corners, openings and reinforcement.
| Nominal width | Nominal size | Specified size, in | Specified size, mm | Minimum face shell, recent ASTM C90 |
|---|---|---|---|---|
| 4 in | 4 x 8 x 16 | 3 5/8 x 7 5/8 x 15 5/8 | 92 x 194 x 397 | 0.75 in |
| 6 in | 6 x 8 x 16 | 5 5/8 x 7 5/8 x 15 5/8 | 143 x 194 x 397 | 1 in |
| 8 in | 8 x 8 x 16 | 7 5/8 x 7 5/8 x 15 5/8 | 194 x 194 x 397 | 1.25 in |
| 10 in | 10 x 8 x 16 | 9 5/8 x 7 5/8 x 15 5/8 | 244 x 194 x 397 | 1.25 in |
| 12 in | 12 x 8 x 16 | 11 5/8 x 7 5/8 x 15 5/8 | 295 x 194 x 397 | 1.25 in |
Width, height and length. Millimeters are conversions of the specified inches.
1. 4-inch Cinder Blocks
The 4-inch cinder block, a nominal 4 x 8 x 16, is 3 5/8 inches wide, 7 5/8 high and 15 5/8 long. Recent editions of ASTM C90 let its face shells be as thin as 0.75 inches, and its cores are small enough that 4-inch walls are rarely grouted, although no code forbids it. The 4-inch dimension also turns up as a height, in solid cap units such as the 8 x 4 x 16.
2. 6-inch Cinder Blocks
Six-inch cinder blocks measure 5 5/8 by 7 5/8 by 15 5/8 inches, 143 by 194 by 397 mm, and their half block is a nominal 6 x 8 x 8. This width steps up to a 1-inch minimum face shell under recent editions of ASTM C90, and filling both cores of a two-core 6-inch unit takes about 0.17 cubic feet of grout by one maker’s estimate.
3. 8-inch Cinder Blocks
The 8-inch cinder block is the standard 8 x 8 x 16 CMU, 7 5/8 by 7 5/8 by 15 5/8 inches, with a half block 7 5/8 inches long, a nominal 8 x 8 x 8. Under recent editions of ASTM C90 its face shells have a 1.25-inch minimum and its webs a 0.75-inch one, and both cores of a two-core unit take about 0.25 cubic feet of grout. One maker offers 8-inch units as half-high, starter, three-quarter, bond beam, lintel or horsecollar, 45-degree bay corner, jamb or sash, bullnose and 75 percent solid.
4. 10-inch Cinder Blocks
A 10-inch cinder block, a nominal 10 x 8 x 16, measures 9 5/8 by 7 5/8 by 15 5/8 inches, 244 by 194 by 397 mm, and its half block, a nominal 10 x 8 x 8, is 9 5/8 by 7 5/8 by 7 5/8 inches. Its minimum face shell under recent editions of ASTM C90 is 1.25 inches, the figure for every unit 8 inches wide or wider, and both cores of a two-core 10-inch unit take about 0.33 cubic feet of grout.
5. 12-inch Cinder Blocks
At 11 5/8 inches wide, 7 5/8 high and 15 5/8 long, or 295 by 194 by 397 mm, a 12-inch cinder block takes its name from its nominal width, and its half block is 11 5/8 by 7 5/8 by 7 5/8 inches. It shares the 1.25-inch minimum face shell of the 8- and 10-inch units under recent editions of ASTM C90, both cores of a two-core unit take about 0.39 cubic feet of grout, and one maker offers 12 x 8 x 16 stretcher, L corner and sash units and a 12 x 4 x 16 solid cap.
How Big Are the Holes in Cinder Blocks?
The holes in cinder blocks, called cells or cores, measure at most 5 1/8 by 6 11/16 inches, 130 by 170 mm, in an 8-inch two-cell block made to its specified size under recent editions of ASTM C90, and two cells with three webs is the most common layout of a hollow unit. Those are the inside dimensions left when the 7 5/8 by 15 5/8 inch plan loses two 1.25 inch face shells and three 0.75 inch webs, and since the thicknesses are minimums, a thicker face shell or web makes the cell smaller. Face shells and webs also taper, a draft that lets the unit strip from its mold, so a cell is larger at one bed face than at the other.
Cell layouts vary from maker to maker, and the industry’s and makers’ cell and web drawings are offered as illustrative only. One maker’s 2002 design of the 8 x 8 x 16 hollow stretcher, for instance, has 1 1/4 inch face shells, a 1 inch center web, end flanges of 3/4 and 2 inches and core corners rounded to a 5/8 inch radius. Core counts vary too: one maker sells its 4-inch regular unit with three cores and its 6- to 12-inch regular units with two.
By one maker’s estimate, grouting both cells takes about 0.17 cubic feet for a two-core 6-inch block, 0.25 for an 8-inch, 0.33 for a 10-inch and 0.39 for a 12-inch, while 4-inch cores are small enough that 4-inch walls are rarely grouted.
Cinder Block Sizes and Shapes
Cinder block sizes and shapes go beyond the plain stretcher, with types of unit made for corners, openings, reinforcement and coursing, and the names vary by region and maker. The specials stay on the same 8-inch module: a half block is 7 5/8 inches long in every width and a half-high unit 3 5/8 inches tall carries 4-inch coursing, so they course with the stretchers around them.
| Shape | What it is |
|---|---|
| Stretcher | The standard hollow unit, most often two cells and three webs |
| Corner, single or double | Corner units, the double corner also called a plain end unit |
| Half block | Half length, 7 5/8 in long in every width |
| All-purpose or kerf | Two close center webs, split on site into two half-length units for openings, wall ends and corners |
| Half-high | 3 5/8 in high, for 4 in coursing |
| Bond beam | Reduced or knock-out webs to carry horizontal reinforcement |
| Lintel | A bond beam unit with a solid bottom that confines the grout |
| Sash | A vertical groove in one end for a window or door sash, or a control-joint gasket |
| Open-end or A unit | One end open, so the unit can be threaded around a reinforcing bar instead of lifted over it |
| Control joint | One male and one female end to carry lateral load across the joint |
| Bullnose | A single or double rounded corner |
| Beveled end | A 45 degree end for walls meeting at 135 degrees |
| Pilaster and column | A hollow center that leaves room for vertical reinforcement |
| Solid cap | A solid unit 4 in high nominal, such as 8 x 4 x 16 |
| Solid | Net cross-section at least 75 percent of gross, under ASTM C90 |
What Do ASTM C90 and C129 Cover?
ASTM C90 covers loadbearing concrete masonry units and ASTM C129 covers nonloadbearing units. C90 units may be hollow or solid and serve loadbearing or nonloadbearing walls, and the standard’s physical requirements cover dimensional tolerances, minimum face shell and web thicknesses, minimum strength, maximum absorption and maximum linear drying shrinkage, which it limits to 0.065 percent. The 2024 edition, C90-24a, is titled Standard Specification for Dry-Cast Loadbearing Concrete Masonry Units, and C129-26 covers dry-cast units for nonloadbearing partitions and, under certain conditions, protected exterior walls above grade.
The edition a building code or project specification references is the one that governs, and the number after the designation is the year of its last revision. The minimum net-area compressive strength under current C90 is 2,000 psi, 13.8 MPa, while older references give 1,900 psi, the minimum C90 carried until its 2011 revision raised it to 2,000. C90 was revised in 2011 to admit units other than the conventional two-cell, three-web block, and by 2013 one 0.75-inch web minimum applied to every width, where earlier editions had required up to 1 1/8 inches. Some estimating guides and reproduced older tables still carry those 1 1/8 inch webs for 10- and 12-inch units, with face shells of 1 3/8 and 1 1/2 inches, thicker than the current 1.25-inch minimum for every unit 8 inches wide or wider.
How Much Does a Cinder Block Weigh?
A cinder block weighs about 22 to 36 pounds oven-dry for a standard 8-inch unit, 10.0 to 16.3 kg, across concrete densities of 85 to 135 pounds per cubic foot. A typical medium-weight 8 x 8 x 16 from ORCO weighs about 32 pounds, and Basalite’s 8 x 8 x 16 standard block weighs 40 pounds. How heavy a block is follows both the concrete’s density and the amount of concrete in the unit, so a lightweight 12-inch block can weigh less than a normal-weight 8-inch one. ASTM sorts units into lightweight, under 105 pounds per cubic foot, medium weight, 105 to under 125, and normal weight, 125 and over.
| Nominal width | Approximate weight, lb | Approximate weight, kg |
|---|---|---|
| 4 in | 16 to 25 | 7.3 to 11.3 |
| 6 in | 20 to 32 | 9.1 to 14.5 |
| 8 in | 22 to 36 | 10.0 to 16.3 |
| 10 in | 28 to 48 | 12.7 to 21.8 |
| 12 in | 33 to 52 | 15.0 to 23.6 |
Approximate oven-dry weights for concrete densities of 85 to 135 pounds per cubic foot. One maker's 8-inch standard block weighs 40 pounds.
Project Ideas Inspired From Cinder Block Dimensions
Cinder block projects work best when they are planned on the block’s own module, 8 inches high and 16 inches long per block with its joint, so that walls, beds and benches come out in whole and half blocks. A layout drawn in 16-inch steps along its length and 8-inch courses in height needs no cut blocks, and where a run falls half a block short, a half block, 8 inches nominal, closes it.
1. Garden Bed
A cinder block garden bed uses the blocks as its walls and their open cells as planting pockets. One course of 8-inch blocks gives a wall 7 5/8 inches high, and each course added raises a dry-laid bed by another 7 5/8 inches, or by 8 inches where the blocks are laid in mortar. Block labels do not say which aggregate a block contains, so anyone concerned about growing food against the blocks can seal them with polymer paint. Painted blocks set indoors serve the same purpose for houseplants, and a dry-laid bed can be taken apart and rearranged in a way a mortared stone bed cannot.
2. Painted Shelves
Cinder block shelves stack blocks as uprights and span boards between them, so each 8-inch block on its side sets a shelf at a 7 5/8 inch step and its cells hold books and frames. An 8-inch block weighs about 22 to 36 pounds oven-dry, and the US Consumer Product Safety Commission advises anchoring any furniture with shelves to the wall to prevent tip-overs. Paint gives the blocks color to suit a room, and solid units or caps combined with pavers close the top of each stack.
3. Outdoor Bench
An outdoor cinder block bench lays blocks on their sides as legs, with timbers or a slab across them, and a block on its side stands 7 5/8 inches wide at its base and 15 5/8 inches long. Beveled-end units with a 45 degree end set two runs at 135 degrees for a bench that bends, and corner units finish the square corner of an L-shaped bench. Cushions make the concrete comfortable to sit on, and the bench needs a level, firm base before the first block goes down.
Conclusion
A standard cinder block is a nominal 8 by 8 by 16 inch concrete masonry unit made 7 5/8 by 7 5/8 by 15 5/8 inches, every other width follows the same 3/8 inch rule from 4 to 16 inches, and the two cells of the common unit set what can be grouted, reinforced or planted.
