Instantly convert Specific Weight (γ) to Specific Gravity (SG)
Enter the specific weight of the fluid or material.
Please enter a positive number.
Newtons per cubic meter (N/m³)
Kilonewtons per cubic meter (kN/m³)
Pounds-force per cubic foot (lbf/ft³)
Kilograms-force per cubic meter (kgf/m³)
Select the unit for the value entered above.
Calculated Specific Gravity (SG)
1.000
Reference Water γ9807 N/m³
Estimated Density (ρ)1000 kg/m³
Fluid StateNeutral (Water)
Formula Used: SG = γsubstance / γwater
Where γwater is the standard specific weight of water at 4°C in the selected unit.
Specific Gravity Comparison
Compares your result against common materials.
What is Specific Weight to Specific Gravity Calculator?
A specific weight to specific gravity calculator is an essential engineering tool designed to convert the specific weight (γ) of a substance into its dimensionless Specific Gravity (SG). This conversion is fundamental in fluid mechanics, civil engineering, and geology, as it standardizes the density of a material relative to water.
Engineers and scientists use this calculation to determine buoyancy, pressure gradients in fluids, and material composition without needing to constantly refer to density tables. While specific weight varies with gravity, specific gravity provides a consistent ratio useful for comparison across different environments.
Who Should Use This Tool?
Civil Engineers: For hydraulic calculations and soil mechanics.
Mechanical Engineers: When designing fluid power systems.
Geologists: To identify mineral composition based on weight.
Students: Solving problems in fluid statics and dynamics.
Specific Weight to Specific Gravity Formula
The mathematical relationship between specific weight and specific gravity is derived from the definition of Specific Gravity. It is the ratio of the specific weight of a given substance to the specific weight of a standard reference fluid (typically water at 4°C).
SG = γsubstance / γreference
Where:
Variables used in the specific weight to specific gravity formula
Variable
Meaning
Standard Water Value (Reference)
SG
Specific Gravity (Dimensionless)
1.0
γsubstance
Specific Weight of input material
Variable
γreference
Specific Weight of Water (at 4°C)
9,807 N/m³ (SI) or 62.43 lbf/ft³ (Imperial)
Mathematical Explanation
Specific weight (γ) is defined as weight per unit volume (γ = ρ × g), where ρ is density and g is gravitational acceleration. Since Specific Gravity is also the ratio of densities (SG = ρsubstance / ρwater), and gravity acts equally on both the substance and the reference water in the same location, the ratio of specific weights yields the same dimensionless value.
Practical Examples
Example 1: Hydraulic Oil Calculation
A mechanical engineer measures the specific weight of a hydraulic fluid as 8.5 kN/m³. They need to find the specific gravity to configure a pump system.
Input: 8.5 kN/m³ (which is 8500 N/m³)
Reference (Water): 9.807 kN/m³
Calculation: SG = 8.5 / 9.807
Result: SG ≈ 0.867
Interpretation: The oil is lighter than water and will float if mixed.
Example 2: Concrete Foundation Analysis
A civil engineer works with reinforced concrete having a specific weight of 150 lbf/ft³.
Input: 150 lbf/ft³
Reference (Water): 62.43 lbf/ft³
Calculation: SG = 150 / 62.43
Result: SG ≈ 2.40
Interpretation: The concrete is 2.4 times heavier than an equivalent volume of water.
How to Use This Specific Weight to Specific Gravity Calculator
Enter the Value: Input the known specific weight in the first field. Ensure the number is positive.
Select the Unit: Choose the unit that matches your data (N/m³, kN/m³, lbf/ft³, etc.). The calculator automatically adjusts the reference water value based on your selection.
Review Results: The calculator instantly displays the Specific Gravity.
Analyze Intermediates: Check the "Estimated Density" to see the mass density equivalent, and "Reference Water γ" to understand the divisor used in the formula.
Use the Chart: Compare your material's SG against common substances like Steel, Concrete, and Oil to validate if your result makes physical sense.
Key Factors That Affect Specific Weight Results
When working with a specific weight to specific gravity calculator, several physical factors can influence the accuracy of your results:
Temperature: Fluids expand as temperature rises, decreasing their specific weight. While the reference water is standard at 4°C, your material might be at a different temperature.
Pressure: For gases and compressible liquids, increased pressure increases specific weight significantly.
Gravity (g): Specific weight depends on gravity (γ = ρg). If you measure weight on the moon, specific weight drops, but specific gravity (a mass ratio) theoretically remains constant if the reference is also adjusted. However, standard calculations assume Earth's gravity (9.81 m/s²).
Impurities: Saltwater has a higher specific weight (approx 10.1 kN/m³) than freshwater due to dissolved solids.
Air Entrainment: In fluids like concrete or oil, trapped air bubbles reduce the bulk specific weight.
Measurement Units: Confusing lbf (pounds-force) with lbm (pounds-mass) is a common error. Specific weight uses force units.
Frequently Asked Questions (FAQ)
Q: What is the unit for Specific Gravity?
Specific Gravity is a dimensionless quantity. Because it is a ratio of two weights (Force/Volume divided by Force/Volume), the units cancel out.
Q: Can specific gravity be less than 1?
Yes. If the SG is less than 1.0, the substance is less dense than water and will float (e.g., oil, wood, gasoline).
Q: How does this differ from density?
Density is mass per unit volume (kg/m³), while Specific Weight is weight per unit volume (N/m³). Specific Gravity compares either of these to water.
Q: What is the standard value for water used here?
We use the standard value of water at 4°C: 9807 N/m³ (SI) or 62.43 lbf/ft³ (Imperial).
Q: Can I use this for gases?
Technically yes, but gases are often compared to air rather than water. If comparing to water, the SG will be very small.
Q: Why is Specific Gravity important in finance or costing?
In logistics, shipping costs are often based on weight. Knowing the SG allows estimators to convert volume (cubic meters) to weight (metric tons) accurately for freight calculations.
Q: Does specific weight change with altitude?
Yes, because gravity decreases slightly with altitude, specific weight decreases, whereas density remains constant (ignoring pressure changes).
Q: How do I convert Specific Gravity back to Density?
Multiply the SG by the density of water (1000 kg/m³ or 1.94 slugs/ft³).
Related Tools and Internal Resources
Density Calculator – Calculate mass density from mass and volume inputs.