Calculate Weight Volume Specific Gravity
Accurately determine the Specific Gravity of any material using mass and volume inputs.
kg
g
lb
oz
Enter the total mass (often referred to as weight) of the object.
Please enter a positive mass value.
m³
cm³
Liters
ft³
Gallons
Enter the volume occupied by the object.
Please enter a positive volume value.
Water at 4°C (1000 kg/m³)
Water at 20°C (998 kg/m³)
Air (1.225 kg/m³)
Specific Gravity is usually calculated relative to water.
Specific Gravity (SG)
2.000
Ratio of Substance Density (2000 kg/m³) to Water Density (1000 kg/m³)
Analysis & Intermediate Values
| Metric | Value |
|---|---|
| Calculated Density | 2000 kg/m³ |
| Normalized Mass | 1000 kg |
| Normalized Volume | 0.5 m³ |
| Buoyancy Status | Sinks in Reference |
Density Comparison Chart
Substance Density
Reference Density
Fig 1. Visual comparison of your substance's density against the reference material (usually water).
What is Specific Gravity?
Specific Gravity (SG) is a fundamental concept in physics and engineering that represents the ratio of the density of a substance to the density of a reference substance. When you need to calculate weight volume specific gravity, you are essentially determining how heavy a substance is compared to an equal volume of water.
This dimensionless quantity is critical in various industries, including geology, brewing, automotive mechanics (battery testing), and medical fields (urinalysis). Because it is a ratio, it has no units. If you calculate weight volume specific gravity and the result is greater than 1, the substance is denser than the reference material (usually water) and will sink. If it is less than 1, it will float.
Common misconceptions include confusing Specific Gravity with Density. While they are directly related, Density has units (like kg/m³ or lb/ft³), whereas Specific Gravity is a pure number derived from the relationship between weight and volume relative to a standard.
Calculate Weight Volume Specific Gravity: Formula and Math
To accurately calculate weight volume specific gravity, you must first determine the density of your object. The process involves two main steps derived from the standard definition.
Step 1: Calculate Density (ρ)
Density = Mass / Volume
Density = Mass / Volume
Step 2: Calculate Specific Gravity (SG)
SG = Density of Substance / Density of Reference
SG = Density of Substance / Density of Reference
In most cases, the reference substance is water at 4°C, which has a density of approximately 1000 kg/m³ (or 1 g/cm³).
Variables Table
| Variable | Meaning | Common Units | Typical Range |
|---|---|---|---|
| m | Mass (often called Weight) | kg, g, lbs | > 0 |
| V | Volume | m³, L, cm³ | > 0 |
| ρ (rho) | Density | kg/m³ | 0.001 – 22,000+ |
| SG | Specific Gravity | None (Unitless) | 0.5 – 20.0 |
Practical Examples (Real-World Use Cases)
Example 1: Testing a Gold Nugget
A prospector finds a yellow rock and wants to verify if it is gold. He measures the mass as 0.386 kg and displaces water to find the volume is 20 cm³ (0.00002 m³). He needs to calculate weight volume specific gravity to verify the material.
- Mass: 0.386 kg
- Volume: 0.00002 m³
- Density Calculation: 0.386 / 0.00002 = 19,300 kg/m³
- SG Calculation: 19,300 / 1000 = 19.3
- Conclusion: Pure gold has an SG of approx 19.3. The rock is likely pure gold.
Example 2: Brewing Beer
A homebrewer measures the sugar content of their wort before fermentation. They take a sample weighing 1.050 kg for every 1 liter (0.001 m³).
- Mass: 1.050 kg
- Volume: 1 Liter (0.001 m³)
- Density: 1050 kg/m³
- SG: 1050 / 1000 = 1.050
- Interpretation: The specific gravity is 1.050, indicating the sugar concentration suitable for fermentation.
How to Use This Calculator
Our tool simplifies the math required to calculate weight volume specific gravity. Follow these steps:
- Enter Mass: Input the weight of your object. Select the correct unit (kg, lbs, etc.).
- Enter Volume: Input the physical space the object occupies. For irregular objects, this is often found via water displacement.
- Select Reference: Default is Water (4°C). Change this only if you are comparing against a different fluid like air or warm water.
- Analyze Results: The calculator instantly provides the SG. It also generates a chart comparing your object's density to water.
Use the "Copy Results" button to save your data for reports or lab notes. The tool automatically handles unit conversions, ensuring you always get a precise SI-standard result.
Key Factors That Affect Results
When you calculate weight volume specific gravity, several external factors can influence the accuracy of your results:
- Temperature: Both the substance and the reference water change volume with temperature. Water is most dense at 4°C. Warmer water is less dense, which alters the SG ratio.
- Pressure: For liquids and solids, pressure has a negligible effect. However, if you are measuring gases, pressure dramatically changes volume and density.
- Porosity: If a solid has internal air pockets (like volcanic rock), the "bulk specific gravity" will be lower than the true specific gravity of the mineral itself.
- Impurities: Dissolved salts or minerals in the reference water (like seawater vs. fresh water) change the reference density, affecting the calculation.
- Measurement Error: Small errors in volume measurement, especially for small objects, can lead to large errors in the final SG value.
- Surface Tension: When measuring volume via displacement, surface tension can trap bubbles on the object, artificially increasing the volume reading and lowering the calculated SG.
Frequently Asked Questions (FAQ)
1. What is the unit for Specific Gravity?
Specific Gravity is unitless. It is a ratio of two densities, so the units cancel out.
2. How do I calculate weight volume specific gravity for liquids?
The process is the same. Weigh a known volume of the liquid and divide that weight by the volume to get density, then divide by the density of water. Hydrometers can also measure this directly.
3. Why is water used as the reference?
Water is abundant, chemically stable, and has a convenient density of approximately 1 g/cm³ or 1000 kg/m³, making calculations simple.
4. Can Specific Gravity be negative?
No. Mass and volume are physical properties that cannot be negative, so the ratio cannot be negative.
5. Does gravity affect specific gravity?
Technically, no. While "weight" depends on gravity, mass does not. Specific Gravity is based on density (Mass/Volume). However, if you measure weight (force) instead of mass, local gravity cancels out if both object and reference are weighed in the same location.
6. What is the difference between SG and API Gravity?
API Gravity is a specific scale used in the petroleum industry derived from Specific Gravity. It serves a similar purpose but uses a different numerical scale.
7. How does buoyancy relate to SG?
Archimedes' principle states that an object with an SG less than 1 will float in water, while an object with an SG greater than 1 will sink.
8. Can I use this to calculate the weight of an object if I know the SG?
Yes! If you know the volume and the SG, you can rearrange the formula: Mass = SG × Volume × Density of Water.
Related Tools and Internal Resources
Explore our suite of engineering and physics calculators designed to help you solve complex problems quickly:
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- Geometric Volume Calculator – Calculate volume for cylinders, spheres, and cubes.
- Buoyancy Force Calculator – Determine the upward force on submerged objects.
- Mass vs. Weight Calculator – Understand the difference between mass and force.
- Fluid Mechanics Formulas – A comprehensive guide to fluid dynamics.
- Periodic Table of Elements Density List – Reference densities for all chemical elements.