How to calculate the unit weight of concrete?

The article aims to answer the question “How to calculate the unit weight of concrete?”. It will also highlight the method you can estimate the required weight of concrete to make slabs. The article will also discuss the benefits and problems associated with lightweight and fly ash concrete.

How to calculate the unit weight of concrete?

  • By utilizing equations that link density, weight, mass, and volume to one another, you may estimate the density of concrete or other solid materials and their mass or weight. 
  • Concrete’s unit weight and steel’s unit weight can also be multiplied by the object’s volume to determine the weight.
  • It is possible to calculate the weight of a substance by multiplying its density by the volume and then dividing the result by a known mass-to-volume ratio (such as concrete’s density). 
  • In contrast to mass, weight is a measure of the gravitational pull exerted on an item by a planet. With a material’s weight in kilograms, you can calculate its Newtonian mass by multiplying its mass in kilograms by a value known as the gravitational constant, 9.8 m/s2.
  • Using the specific weight equation, you may convert concrete and steel density into specific weight. You may calculate a specific weight by multiplying the density and gravitational acceleration g.
  • The specific weights of 17150 N/m3, 23520 N/m3, and 76930 N/m3 can be determined by multiplying the densities of 1750 kg/m3, 2400 kg/m3, and 7850 kg/m3, respectively, by 9.8 m/s2.

How can I calculate the weight of a square foot of concrete?

  • You may use the following formula to get its weight in pounds per square foot if you know how thick your concrete is.
  • Take the thickness of your concrete and divide it by 12. (this gives you the depth in feet.)
  • As an illustration: Dividing six by twelve gives you five percent (a 6-inch slab is .5 feet thick)
  • One hundred forty-five pounds per cubic foot x.5 = 72.5 pounds per cubic foot or 72.5 pounds per cubic meter.
  • A 6-inch thick slab weighs 72.5 pounds per square foot, the maximum allowable weight.

How much does concrete weigh?

The amount of air and water it contains may affect the weight of concrete. The importance of cement may range from 830 to 1650 kilograms per cubic meter, equivalent to 52 to 103 pounds per cubic foot.

Denser cement is obtained by storing and transporting cement subjected to vibration, as opposed to glue placed into silos pneumatically. Consider that a 94 lb. a bag of newly packed cement equals one cubic foot when weighed.

Lightweight concrete density is 1920 kg per cubic meter (116 lbs per cubic foot) or 116 kilograms per cubic meter (3132 lbs per cubic yard). It weighs less because it is created of pumice, an inherently light mineral.

It is a mass to volume ratio that determines density. The simplest and most accurate method for determining the density of concrete is to fill a specified volume container and weigh it.

Checking concrete strength using test cylinders benefits knowing, comprehending, and monitoring density. In most cases, a decrease in concrete density results in a reduction of concrete strength.

These strength tests may be performed every 24 hours, seven days, and 28 days in a laboratory to detect potential weakness (or lower density). This is critical because concrete is utilized in so many high-strength structures (bridges and high-rises).

In the case of concrete countertops or inside radiant floor heating, you may question whether utilizing lightweight concrete will reduce stress on cabinets and flooring below.

It weighs roughly 18 pounds per square foot for conventional weight concrete and about 14.5 lbs per square foot for lightweight concrete.

Even though concrete countertops weigh less than regular concrete, it’s still simpler to polish standard density concrete because of the 3.5 pounds per square foot weight savings.

Using a vast concrete area for flooring might save a significant amount of weight. Keep in mind that the cost of lightweight concrete is generally twice as much as that of ordinary concrete.

What is the weight of structural lightweight concrete?

For comparison, ordinary concrete weighs 150 pounds per cubic foot, whereas lightweight structural concrete weighs around 105 pounds per cubic foot. 

It is possible to reduce the density of lightweight concrete by using a lesser quantity of light coarse particles and light fine aggregates.

Expanded clay, clay, or slate materials turned into a porous structure mimicking volcanic rock are often used in lightweight aggregate materials. Certain mixtures of slag from air-cooled blast furnaces may also be used.

Structures may benefit from smaller columns, footings, and other components that carry the weight of the building’s contents because of this.

In terms of compressive strength, lightweight structural concrete may be built to be as strong as normal-weight concrete. The mechanical and physical qualities of regular-weight concrete are identical to those of lightweight concrete.

In most projects, the higher cost of lightweight concrete is offset by fewer structural components, less reinforcing steel, and a smaller volume of concrete.

This will result in a more fire-resistant structure when using lightweight concrete. It provides wall components with higher R-values for improved insulation. It all comes down to these two variables when it comes to lightweight concrete as a construction material.

The aggregates must be wetted before use to obtain a high degree of saturation. This may happen if the mix isn’t entirely saturated with aggregates.

An airtight seal encases the bulk of lightweight concrete. The air content must be monitored and maintained to ensure that density requirements are satisfied.

Polishing lightweight concrete requires a higher degree of caution. The light stones will separate from the mortar if the slump is too severe or too much water present. Avoid blisters and delaminations on hand-trodden interior flooring.

When it comes to the drying time of lightweight concrete, it tends to be longer than that of ordinary concrete. While painting the last coat, keep this in mind.

In concrete and steel buildings like parking structures, tilt-up walls, composite slabs on metal decking and piers and beams, lightweight structural concrete has been used to make bridge decks and other structural components (SLC).

If you have a wood-framed deck, a quantity of lightweight concrete may be used to restrict the warm air from escaping.

When dealing with lightweight concrete, pumping the material may be a challenge. A sound pump installation may be achieved by taking certain precautions ahead of time.

What is fly ash concrete?

Fly ash concrete is basically the same as regular concrete except some of the cement has been replaced with a material called fly ash. Before coal is consumed in a power plant, it is first ground into a fine powder.

This coal powder is blown into the power plant’s boiler, the carbon is consumed leaving molten particles rich in silica, alumina, and calcium.

These non-combustible particles solidify as microscopic, ball bearing like, glassy spheres that are collected from the power plant’s exhaust before they can fly away. This leftover ash from burning the coal is called fly ash.

Chemically, fly ash is a pozzolan. When mixed with lime (calcium hydroxide), pozzolans combine to form cementitious compounds. Fly ash in concrete contributes to a stronger, more durable, and more chemical resistant concrete mix.

The main benefit of fly ash for concrete is that it not only reduces the amount of non-durable calcium hydroxide (lime), but in the process converts it into calcium silicate hydrate (CSH), which is the strongest and most durable portion of the paste in concrete.

The paste is the key to strong and durable concrete, assuming average quality aggregates are used. At full hydration, concrete made with regular cements produces approximately 1/4 pound of non-durable lime per pound of cement in the mix.

A typical concrete mix having 470 pounds of cement per cubic yard has the potential of producing 118 pounds of lime. Fly ash chemically reacts with this lime to create more CSH, the same “glue” produced by the hydration of cement and water.

By producing more CSH the paste becomes stronger over time and also closes off more of the capillaries that allow the movement of moisture through the concrete. The result is a stronger, more durable concrete that is less permeable, which aids in the reduction of efflorescence.

Efflorescence (white, chalky substance on the surface) is caused by the face of the concrete being wetted and dried repeatedly, or by the movement of water vapor from the damp side of the concrete to the dry side through the capillaries (voids), drawing out the water soluble lime from the concrete.

The “ball bearing” effect of fly ash creates a lubricating effect when concrete is in its plastic state.


Several variables affect the unit weight of concrete, including the quantity of water and air in the mix. To put it another way, a block of concrete that is one foot wide, one foot long, and one foot high would typically weigh 150 pounds when measured in pounds per cubic foot (lb/ft3).

Assuming that a cubic foot of concrete weighs 2400 kilograms per cubic foot, a block of concrete that is one meter wide, one-meter long, and 1-meter high would weigh 2400 kilograms.

Frequently asked questions (FAQS): How much does concrete weigh?

How to calculate the unit weight of concrete?

By utilizing equations that link density, weight, mass, and volume to one another, you may estimate the density of concrete or other solid materials and their mass or weight. 

Concrete’s unit weight and steel’s unit weight can also be multiplied by the object’s volume to determine the weight.

When cured, does concrete get heavier?

As the cement hardens, the quantity of water that interacted with the cement is reflected in the cement’s weight difference from when it was fresh. A bag of hardened cement will always be heavier than a fresh bag because of this.

Concrete or sand is heavier?

Almost usually, water at its densest is used as a benchmark for liquids! In comparison, the density of sand ranges from 2.65 to 2.67. Cement is heavier than sand in terms of scientific weight!

How much weight can a four-inch thick concrete slab withstand? 

On an uncertain 4-inch slab, we typically restrict the weight to roughly 40 lb/sq ft. 80 pounds per square foot may be possible in certain circumstances, but unless you have an idea of the slab’s bearing and reinforcing capacity, you run the risk of breaking.


El-Dieb, A. S. (2007). Self-curing concrete: Water retention, hydration and moisture transport. Construction and Building Materials, 21(6), 1282-1287.

Sakr, K., & El-Hakim, E. (2005). Effect of high temperature or fire on heavy weight concrete properties. Cement and concrete research, 35(3), 590-596.