Concrete Block Weight: Per Unit, Per Wall, and What It Can Carry

How much does a concrete block weigh?

Block weight is density multiplied by the volume of concrete in the unit. Both halves of that vary, which is why published weights for the same nominal block scatter so widely.

The volume figure below comes from the unit's own geometry: two face shells at 1.25 inches and three webs at 0.75 inches, the ASTM C90 minimums for an 8 inch nominal unit, subtracted from the specified unit dimensions of 15 and 5 over 8 by 7 and 5 over 8 by 7 and 5 over 8 inches. That gives 385.7 cubic inches, or 0.223 cubic feet of concrete per unit.

CMHA is explicit that this is an estimate standing in for a test. The actual volume of a unit is determined under ASTM C140, and absent that result, the specified dimensions give sufficient accuracy for estimating.

Why published weights disagree

Search for the weight of an 8 inch block and you will find figures from the high twenties to the low forties. Most of that spread is real, and it comes from three places.

Density class. ASTM recognizes three classes by oven dry density of the concrete. A lightweight unit and a normal weight unit of identical geometry differ by roughly 40 percent in weight.

Material volume above the minimum. The table above uses C90 minimum thicknesses, which produce the lightest unit the standard permits. Producers routinely make units with thicker webs, more webs, or a thicker interior face shell for thermal mass. A typical production unit carries noticeably more concrete than the minimum, which is why 38 pounds circulates as a design value for a normal weight 8 inch unit while the C90 minimum geometry at 125 pounds per cubic foot gives 28.

Neither figure is wrong. One is the floor the standard allows, the other is what a typical unit off a yard actually weighs. If the number matters, weigh the unit you are buying or ask the producer.

Taper. Every hollow unit made today has tapered face shells and webs so it can be stripped from the mold. The specified thickness is measured at the thinnest point, so there is always a little more material than the specified dimensions suggest.

Weight of a block wall

For dead load, lintel sizing, footing design and sound transmission work, the number that matters is not the unit weight. It is the assembly weight in pounds per square foot of wall, which adds mortar and grout to the units.

CMHA publishes this directly. The table below is for an 8 inch single wythe wall, by unit density and vertical grout spacing.

Read it against a real wall. A 20 foot by 8 foot wall is 160 square feet. At 125 pounds per cubic foot, hollow and ungrouted with face shell bedding, that is 34 pounds per square foot, or 5,440 pounds of wall. Solid grouted at 8 inch spacing it is 84 pounds per square foot, or 13,440 pounds. The same wall, two and a half times the load on whatever is underneath it.

Grout is the single largest variable. Going from ungrouted to solid grouted more than doubles the assembly weight at every density. If you are estimating the grout itself rather than its weight, use the block fill calculator.

The table assumes mortar at 125 pounds per cubic foot, grout at 140, three eighths inch joints, face shell bedding except where noted, and horizontal grout placement at 16 inches on center. Change any of those and the figures move.

How much weight can a concrete block hold?

This is a different question from how much it weighs, and it is where most published answers go wrong.

ASTM C90 sets a minimum net area compressive strength of 2,000 psi for loadbearing units. Net area is the concrete actually in contact at the bed joint, which for a face shell bedded hollow wall is the two face shells only.

Multiply the two: an 8 inch hollow unit, face shell bedded, has about 40 square inches of bearing area, so it reaches its minimum tested strength at roughly 80,000 pounds. Per linear foot of wall, 30 square inches at 2,000 psi is about 60,000 pounds.

That number is not the load you can put on a wall. It is what a single unit must survive in a laboratory compression test before it can be sold as C90 compliant. Four things sit between it and an allowable design load:

The wall's specified compressive strength, f'm, is a function of both the unit strength and the mortar type, not the unit alone. Design strength is a fraction of f'm, with safety factors applied under TMS 402. Slenderness reduces capacity as the wall gets taller relative to its thickness. Eccentric load, meaning any load not applied through the center of the wall, reduces it further.

In practice a block wall almost never fails by crushing the block. It fails by buckling, by overturning, at an eccentric bearing point, or at the footing. Any of those governs long before 2,000 psi does.

If you need a real number for a real load, that is an engineering calculation and it needs an engineer. What this page can tell you is the unit property and why it is not the answer by itself.

Pallets and delivery

Pallet quantities are set by the producer and are not standardized, so a pallet weight is unit weight multiplied by whatever that producer loads. The arithmetic is simple once you know both.

At a commonly loaded 90 units per pallet, a normal weight 8 inch block at the C90 minimum geometry gives about 2,500 pounds per pallet, and a typical production unit at 38 pounds gives about 3,400. That difference decides whether a half ton pickup is enough. Confirm the count and the weight with the supplier before you book delivery.

What this page does not cover

Unit weights here are for hollow loadbearing units under ASTM C90. Solid units, ASTM C129 nonloadbearing units, and architectural units with ground or split faces carry different geometry.

Assembly weights are for 8 inch single wythe walls. Multi wythe walls, cavity walls and walls with veneer are outside the table.

Nothing here is a structural design. For sizes and tolerances, see cinder block dimensions. For what the ASTM specifications actually require, see what is a CMU block. For unit counts, use the cinder block calculator. Because a gravity wall holds soil with its own mass, unit weight matters most of all for retaining wall cinder blocks, and sizing a gravity retaining wall by block, base pad and gravel is its own calculator.

Sources

CMHA CMU-TEC-002-23, Weights and Section Properties of Concrete Masonry Assemblies. Assembly weights by density and grout spacing, net and average section properties, and the unit volume calculation method.

CMHA CMU-TEC-001-23, Concrete Masonry Unit Shapes, Sizes, Properties, and Specifications. Density classes, ASTM C90 minimum face shell and web thicknesses, minimum compressive strength, and unit taper.