# Specific Gravity vs. Specific Weight: What's the Difference?

Edited by Aimie Carlson || By Janet White || Published on December 13, 2023
Specific gravity is the ratio of the density of a substance to the density of a reference substance; specific weight is the weight per unit volume of a substance.

## Key Differences

Specific gravity, a dimensionless quantity, is used to compare the density of a substance to that of a standard reference, usually water. Specific weight, on the other hand, is a measure of how heavy a substance is in relation to its volume, expressed in units like N/m³.
The specific gravity of a substance remains constant regardless of the system of units used, as it is a ratio. In contrast, specific weight varies with the local gravity field, as it is a weight per unit volume.
Specific gravity is typically used in fluid mechanics, geology, and material science to compare substances. Specific weight is crucial in engineering, particularly in fluid mechanics and material density calculations.
Specific gravity is calculated by dividing the density of a substance by the density of a reference substance. Specific weight involves the actual weight force exerted by the substance per unit volume, taking gravity into account.
The value of specific gravity for a substance can provide insight into its buoyancy characteristics. Specific weight is used to determine the load that a substance can exert in a given volume, important for structural engineering calculations.

## Comparison Chart

### Definition

Ratio of a substance's density to a reference density.
Weight per unit volume of a substance.

### Units

Dimensionless (no units).
Newton per cubic meter (N/m³) or equivalent.

### Dependence on Gravity

Not dependent on gravity.
Dependent on local gravity.

### Field of Use

Used in comparing densities in various fields like geology.
Used in engineering for load and pressure calculations.

### Calculation

Density of substance ÷ Density of reference.
Weight of substance ÷ Volume of substance.

## Specific Gravity and Specific Weight Definitions

#### Specific Gravity

It is important in fluid dynamics to understand fluid behavior.
Oil floats on water due to its lower specific gravity.

#### Specific Weight

Specific weight is important in calculating the load-bearing capacity of materials.
The bridge's design considered the specific weight of the used steel.

#### Specific Gravity

Specific gravity is the ratio of the density of a substance to that of a standard substance (usually water).
The specific gravity of mercury is much higher than that of water.

#### Specific Weight

It is used in engineering to determine pressure exerted by fluids.
In hydraulic systems, the specific weight of the fluid affects the pressure.

#### Specific Gravity

It's a dimensionless quantity that indicates how dense a substance is compared to water.
A specific gravity less than 1 means the substance is less dense than water.

#### Specific Weight

Specific weight varies with the location due to changes in gravitational acceleration.
The specific weight of water is different at high altitudes compared to sea level.

#### Specific Gravity

Specific gravity is crucial in geology for mineral identification.
The specific gravity test revealed the mineral to be quartz.

#### Specific Weight

Specific weight is the weight of a material per unit volume.
The specific weight of concrete is critical in building construction.

#### Specific Gravity

Specific gravity is used in various industries to characterize materials.
The specific gravity of a gemstone helps in identifying its type.

#### Specific Weight

It's expressed in force per unit volume, such as Newtons per cubic meter.
Engineers calculated the specific weight of the soil to assess stability.

## FAQs

#### Does specific gravity depend on gravity?

No, specific gravity is independent of gravity as it is a ratio of densities.

#### Can specific gravity be more than 1?

Yes, if a substance is denser than the reference substance, its specific gravity can be more than 1.

#### What unit is specific weight measured in?

Specific weight is typically measured in Newtons per cubic meter (N/m³).

#### What is an application of specific weight?

Specific weight is used in engineering for load and pressure calculations.

#### Is specific gravity used in the jewelry industry?

Yes, it is used to identify and categorize gemstones.

#### What is specific gravity?

Specific gravity is the ratio of the density of a substance to the density of a reference substance, usually water.

#### How is specific weight defined?

Specific weight is the weight of a substance per unit volume.

#### Is specific weight affected by gravity?

Yes, specific weight varies with the gravitational force.

#### Where is specific gravity used?

Specific gravity is used in geology, fluid mechanics, and material science.

#### How do you calculate specific gravity?

Specific gravity is calculated by dividing the density of a substance by the density of a reference substance.

#### What factors affect specific weight?

The local gravitational force and the density of the substance affect specific weight.

#### What is the significance of specific gravity in brewing?

In brewing, specific gravity helps determine the alcohol content of the beverage.

#### Can specific weight be used to determine fluid pressure?

Yes, it is essential in calculating the pressure exerted by a fluid.

#### Does specific weight change with location?

Yes, as gravity varies with location, so does specific weight.

#### Why is specific gravity important in fluid dynamics?

It helps understand the buoyancy and flow characteristics of fluids.

#### Does specific weight play a role in hydraulic engineering?

Yes, it is crucial in designing hydraulic systems and understanding fluid behavior.

#### Can specific gravity be used to test battery acid?

Yes, it is used to determine the charge level of lead-acid batteries.

#### How does temperature affect specific gravity?

Specific gravity can change with temperature, as it affects the density of substances.

#### Is specific weight a factor in aircraft design?

Yes, it is considered in calculating the weight and balance of aircraft.

#### Is specific weight important in structural engineering?

Absolutely, it helps in calculating the load-bearing capacity of structures.