Concrete Block Weight: How Much Does a Cinder Block Weigh?

Cinder block, concrete block or CMU?

The industry term is concrete masonry unit, or CMU. "Cinder block" is what most people say, and it is worth clearing up what it means, because the usual explanation is wrong.

The common story online is that cinder blocks were made with coal cinders a century ago and are no longer produced. The Concrete Masonry and Hardscapes Association, the industry body that would know, says the opposite. Its FAQ on the difference between a cinder block and a concrete block states that the two are "essentially the same product produced with the same three basic constituent materials: water, cement, and aggregate," and that "the practice of incorporating coal combustion cinders (as well as other waste by-products) into concrete masonry units continues today."

CMHA also makes the point that matters for weight: you cannot tell by looking, and "the density of a block is not an indication of whether it has been manufactured with or without cinders." Some producers use volcanic cinders as their lightweight aggregate and say so openly.

So "cinder block" is a legacy consumer word, not a product category, and it tells you nothing about weight. What determines weight is the oven-dry density of the concrete the unit was made from, plus how much of the unit is actually solid.

The three ASTM C90 density classes

ASTM C90 is the standard specification for loadbearing concrete masonry units, and it sorts them by oven-dry density into three classes:

Those boundaries appear identically in CMHA's CMU-TEC-001-23 on unit shapes, sizes, properties and specifications and in NCMA TEK 2-6 and TEK 1-1F, all quoting C90 directly. A single "cinder block weighs 28 pounds" claim is really a claim about one size at the lightweight end, presented as though it covered all of them.

Which class you get depends on where you are. Industry commentary notes that medium weight became the inventory standard in much of the country but that many producers have shifted to normal weight as expanded slag got scarce and expensive, while in parts of the west lightweight and medium weight dominate and normal weight is the exception. The practical upshot is that the honest answer to "how much does a block weigh" is a range, and your block yard knows which end of it you are buying.

Nominal size is not actual size

A nominal 8x8x16 block actually measures 7-5/8 by 7-5/8 by 15-5/8 inches. CMHA's specification document explains why: specified dimensions are 3/8 inch less than nominal "so that a 4 or 8 in. module is maintained with 3/8 in. mortar joints." The block plus its mortar joint equals the nominal number, which is what keeps a wall on a module.

That 3/8 inch matters for weight, because it takes about 7 percent out of the gross volume before you account for the cores.

A hollow unit is roughly 50 to 60 percent of that gross volume in actual concrete. C90 sets minimum face shell thicknesses of 3/4 inch for 3 and 4 inch units, 1 inch for 6 inch units and 1-1/4 inches for 8 inch and wider, with a minimum web thickness of 3/4 inch throughout.

Concrete block weight chart

Before the chart, a disclosure that no other page on this topic seems willing to make: no standards body publishes a per-unit weight chart in pounds. ASTM, CMHA and NCMA publish density classes in pounds per cubic foot and wall weights in pounds per square foot, and they expect unit weight to be computed as net volume times density. CMHA's own method says as much, noting that unit volume "can be estimated with sufficient accuracy using the specified dimensions of the unit." Every block weight chart in circulation is therefore either one manufacturer's figures or somebody's arithmetic.

This one is our arithmetic, from the gross volumes above at 50 to 60 percent solid, at four densities. We validated it against published retailer figures and it agrees within about a pound, which is noted under the table.

Solid and part units, calculated the same way:

• 8 x 8 x 16 solid: about 66 pounds at 125 lb/ft³, 71 pounds at 135.
• 4 x 8 x 16 solid: about 31 pounds at 125 lb/ft³, 34 pounds at 135.
• Half block, 8 x 8 x 8 hollow: about 18 to 19 pounds.
• Concrete brick, nominal 4 x 2 x 8 solid: about 4 to 5 pounds. Note that concrete brick is covered by ASTM C55, not C90.

How we checked it. Angelus Block publishes 18 pounds for its 8x8x8 half block, against our calculated 18 to 19. Home Depot lists 30 pounds for a 6 inch hollow unit, against our 26 to 31 at 135 lb/ft³. Home Depot lists 31.5 pounds for a 4 inch unit, which only makes sense as a solid block, and our solid 4 inch figure is 31 to 34. And the same method reproduces CMHA's published 84 pounds per square foot for a fully grouted 8 inch wall at 125 lb/ft³ to within 2 percent. Four independent checks, all inside a pound or two.

Why an older block is heavier than a new one

If you are matching new block to an existing wall, or comparing a chart you found in an old reference to what your supplier stocks, there is a reason the numbers disagree.

ASTM C90 changed in 2011. NCMA TEK 1-1F records that "in 2011, web thickness requirements were significantly revised," and that in C90-11b the previous rules "were replaced with a single minimum web thickness (0.75 in., 19.1 mm), regardless of unit width," with "equivalent web thickness" replaced by a normalized web area of at least 6.5 square inches per square foot of face area.

The practical effect, as ESCSI describes it, is that where an 8 inch block previously needed three 1 inch webs, it can now be made with one web as thin as 0.75 inch. STRUCTURE magazine's account of the change agrees. Less concrete in the webs means a lighter unit at the same density.

So a code-compliant 8x8x16 made today can be meaningfully lighter than one made before 2011 at the same density class. It also explains why older published wall weight tables run heavier than current ones. The density classes themselves have not changed.

What the retailers actually publish

Worth knowing before you rely on a product page. These are retailer-listed figures, not standards.

Three caveats. Home Depot's listings disagree with each other on the same product, 37 pounds in the specification table against 39 in the summary. Several listings, including the 10 and 12 inch units, publish no weight at all. And no retailer states the ASTM C90 density class, which is the one variable that actually determines the answer. Lowe's goes further and publishes no weight on its standard block listings, though it does give the actual dimensions and sometimes the weight class in the product title.

What the retailer figures do confirm is the chart above: 37 to 37.5 pounds sits inside our calculated 35 to 43 pound normal-weight band.

Wall weight per square foot

For a footing design, a lintel or a structural check, the useful figure is the assembly weight, not the unit weight. These include the mortar, and assume 125 lb/ft³ mortar and 140 lb/ft³ grout, which are the densities the industry documents use.

Those are the 2002 edition's figures, so they reflect the heavier pre-2011 web geometry. A current 8 inch unit at the same density will come in lighter, which is the C90 change described above. Treat them as a conservative upper bound rather than a precise number for block made today.

Fully grouted walls are better documented and the sources agree closely. The figures below come from a compilation citing ASTM C90 and NCMA TEK 14-1B and 14-13B, and they match Angelus Block's own published wall weights within 1 to 3 pounds per square foot at every size and class, which is strong agreement from two independent lineages.

Grouting an 8 inch wall roughly doubles its weight, from the high thirties or forties to the low eighties. If you are sizing a footing, that is the single biggest decision on the page. The concrete wall calculator handles the concrete volume for a poured wall instead.

Grout and mortar quantities

Grout is 140 lb/ft³ and mortar is 125 lb/ft³, both stated in CMHA and NCMA documents. Lightweight grout at 105 lb/ft³ exists and changes the answer, so check what you are specifying.

For quantities, CMHA's worked example assigns mortar 2.0 pounds per square foot of wall for face shell bedding with no excess, which at 125 lb/ft³ is about 1.6 cubic feet of mortar per 100 square feet. That is in-place mortar. Real ordering allowances run several times higher once you account for waste, joint overfill and full bedding, and we have not found an authoritative published waste allowance, so treat any figure you see as an estimating convention rather than a standard. The mortar calculator handles the practical version.

For grout, no standards document we could reach publishes a cubic-feet-per-100-square-feet table, so here is the derivation. Gross wall volume per square foot minus net block volume per square foot, at 55 percent solid units:

• 6 inch wall: about 23 cubic feet per 100 square feet, weighing 32 lb/ft²
• 8 inch wall: about 31 cubic feet per 100 square feet, weighing 43 lb/ft²
• 10 inch wall: about 39 cubic feet per 100 square feet, weighing 55 lb/ft²
• 12 inch wall: about 47 cubic feet per 100 square feet, weighing 66 lb/ft²

So filling the cores of 100 square feet of 8 inch wall takes roughly 31 cubic feet of grout, about 1.15 cubic yards, weighing about 4,300 pounds. That is our calculation, and the check on it is that adding block, grout and mortar this way gives 86 lb/ft² against CMHA's published 84, within 2 percent. It moves with percent solid and core configuration, so confirm against your unit's published net volume.

What a pallet of block weighs

There is no standard pallet count for concrete block. Configuration is set by the individual plant and varies with unit size, plant equipment and local truck weight limits, so anybody quoting you a universal "blocks per pallet" figure has made it up.

What you can do is the arithmetic, once your supplier tells you the count. At a 37 pound unit weight, a 90 unit pallet is about 3,330 pounds of block and a 108 unit pallet about 4,000 pounds, plus 30 to 50 pounds for the pallet itself.

Note what that means. A single pallet of 8 inch block is at or over the payload rating of most half-ton and three-quarter-ton pickups. Half-ton means 1,000 pounds of payload, and 3,330 pounds is more than three times that. Block gets delivered on a boom truck for a reason.

Lifting: what is actually regulated

You will find a "45 pound limit" or a "50 pound limit" for masonry units repeated widely. Neither is a US standard. We could not locate either figure in OSHA regulation, in an OSHA interpretation, in NIOSH publications, in ASTM C90, or in any CMHA or NCMA document.

Here is what is real. OSHA, in a 2013 letter of interpretation, states plainly: "OSHA does not have a standard which sets limits on how much a person may lift or carry." There is no legal maximum lifting weight in the United States.

What exists instead is the NIOSH lifting equation. The same OSHA letter summarises it: the equation "establishes a maximum load of 51 pounds, which is then adjusted to account for how often you are lifting, twisting of your back during lifting, the vertical distance the load is lifted, the distance of the load from your body, the distance you move while lifting the load, and how easy it is to hold onto the load."

That 51 pounds is the load constant for an ideal lift: directly in front of you, at knuckle height, close to the body, no twisting, infrequent, with a good handhold. Block laying violates nearly all of it. You lift all shift, you reach and twist to the wall line, you lift from near the ground and above your shoulders, and a rough hollow unit is a poor handhold. Once the NIOSH multipliers are applied, the recommended weight limit for real masonry work drops well below 51 pounds, commonly into the twenties or low thirties.

Which is exactly the range a normal-weight 8 inch block exceeds. So the defensible statement is not that any poundage is capped, but that a standard normal-weight 8x8x16 routinely exceeds the NIOSH recommended weight limit for the way masons actually lift. CPWR, the construction industry's research arm, names lightweight concrete block as a recognized engineering control for exactly that hazard. That is the sourced version of "lighter blocks are easier on your back," and it connects straight back to the C90 density classes at the top of this page.

Working out your own numbers

To count the block, mortar and courses for a wall, use the concrete block calculator. For the mortar on its own, the mortar calculator. For the weight of poured concrete rather than block, including the density and unit weight questions in more depth, use the concrete weight calculator, and for what a cubic yard of that grout or fill weighs, the weight of a yard of concrete.

One last practical note. Ask your supplier for the density class, not just the size. It is the difference between a 28 pound block and a 43 pound block, and on a thousand-unit job it is the difference between 14 and 21 tons of material to move.