Specific Gravity
SG = ρ_material/ρ_reference (typically water at 4°C). Unitless ratio. API = (141.5/SG) − 131.5 for petroleum. SG > 1 sinks in water; SG < 1 floats.
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Water SG = 1 by definition; ice SG ≈ 0.92 floats. API 10 = heavy crude; API 40+ = light condensate. Archimedes: buoyancy = weight of displaced fluid; SG determines float/sink. Gold SG ≈ 19.3; lead ≈ 11.3; aluminum ≈ 2.7.
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Why: SG identifies materials, indicates float/sink, and is used in petroleum (API), brewing (Plato), and chemical industries. Buoyancy force ∝ (1 − SG).
How: SG = ρ/ρ_ref. API gravity for oils: lighter oils have higher API. Baumé for acids and syrups. Pycnometer: SG = (m_sample − m_empty)/(m_water − m_empty).
Run the calculator when you are ready.
🥇 Gold Purity Test
Verify gold authenticity using specific gravity (SG = 19.3)
🛢️ Crude Oil API
Calculate API gravity for light crude oil (SG = 0.85)
🔋 Battery Acid Test
Check sulfuric acid concentration via specific gravity
🍷 Wine Alcohol Content
Estimate alcohol content from wine specific gravity
💎 Gemstone Identification
Identify gemstone by measuring specific gravity
Enter Values
Calculation Method
Primary Values
Reference
For educational and informational purposes only. Verify with a qualified professional.
🔬 Physics Facts
Archimedes discovered buoyancy in 3rd century BCE; SG determines float/sink.
— History
API gravity: 10° = water density; higher = lighter oil.
— Petroleum
Water at 4°C is reference (max density); 1 g/cm³ = 1000 kg/m³.
— Reference
Pycnometer method gives SG to 4+ decimal places.
— Lab Methods
What is Specific Gravity?
Specific gravity (SG) is a dimensionless quantity that compares the density of a substance to the density of a reference substance, typically water at 4°C for liquids and solids. It indicates whether a material will float or sink in the reference substance and is widely used in petroleum, chemistry, brewing, and materials testing industries.
Relative Density
Compare any substance to water or other reference materials. Unitless ratio for easy comparison across different measurement systems.
Industry Scales
Convert between API gravity, Baumé, Twaddell, Plato, and Brix scales used in petroleum, chemical, and brewing industries.
Multiple Methods
Support for hydrometer, pycnometer, and buoyancy (Archimedes) measurement methods with step-by-step calculations.
How to Measure Specific Gravity
Measurement Methods
- 1. Hydrometer: Float calibrated glass tube in liquid
- 2. Pycnometer: Weigh known volume of liquid precisely
- 3. Buoyancy: Weigh object in air and in water
- 4. Digital Meter: Electronic density measurement
Best Practices
- • Control temperature during measurement
- • Use appropriate reference temperature
- • Remove air bubbles from samples
- • Calibrate instruments regularly
When to Use Specific Gravity
Petroleum Industry
Classify crude oil, price petroleum products, and determine fuel quality using API gravity.
Gemology
Identify gemstones and detect imitations by comparing specific gravity to known values.
Brewing & Food
Monitor fermentation progress, measure sugar content, and ensure product consistency.
Specific Gravity Formulas
Basic Specific Gravity
Dimensionless ratio, water at 4°C as reference
API Gravity (Petroleum)
Higher API = lighter oil, Lower API = heavier oil
Archimedes Principle
For solid objects that sink in water
Frequently Asked Questions
What is the difference between specific gravity and density?
Specific gravity is a dimensionless ratio comparing material density to a reference substance (usually water), while density has units (kg/m³, g/cm³, etc.). Specific gravity makes it easy to compare materials regardless of units, and indicates whether a material will float or sink in the reference substance.
How does temperature affect specific gravity measurements?
Temperature affects density, so specific gravity measurements must account for temperature. Most measurements are standardized to 4°C (water's maximum density) or 20°C. The calculator includes temperature correction factors for accurate measurements at different temperatures.
What does "VERY DENSE", "SINKS", and "FLOATS" mean in the Bloomberg Terminal risk indicator?
The Bloomberg Terminal risk indicator categorizes materials by specific gravity: "VERY DENSE" (SG > 5) indicates extremely dense materials like heavy metals (gold, platinum, tungsten), suitable for radiation shielding and counterweights. "SINKS" (SG > 1) represents materials denser than water that will sink, including most metals and heavy liquids. "FLOATS" (SG < 1) indicates materials lighter than water that will float, including most plastics, wood, and light liquids like gasoline.
What is API gravity and how is it used in the petroleum industry?
API gravity is a measure of how heavy or light petroleum liquid is compared to water. Higher API gravity (above 31.1°) indicates lighter crude oil, while lower values indicate heavier crude. It's used to classify crude oil, determine pricing, and assess refining requirements. The formula is: °API = (141.5 / SG) - 131.5.
How accurate is the buoyancy method for measuring specific gravity?
The buoyancy (Archimedes) method is highly accurate for solid objects, typically within 0.1-0.5% when performed carefully. It requires precise weighing in air and water, ensuring no air bubbles are trapped, and accounting for temperature effects. This method is commonly used for gemstones, metals, and irregularly shaped objects.
Can specific gravity be used to identify materials?
Yes, specific gravity is a valuable identification tool, especially in gemology and materials testing. Each material has a characteristic specific gravity range. For example, gold has SG ≈ 19.3, aluminum ≈ 2.7, and water ≈ 1.0. However, some materials have overlapping ranges, so additional tests may be needed for definitive identification.
What is the difference between Baumé scales for lighter and heavier liquids?
Baumé scale has two formulas: one for liquids lighter than water (Be° = (140 / SG) - 130) and one for liquids heavier than water (Be° = 145 - (145 / SG)). The lighter-than-water scale is used for oils and organic solvents, while the heavier scale is used for concentrated acids and salt solutions.
📚 Official Data Sources
NIST Material Properties Database
National Institute of Standards and Technology material data
Last Updated: 2026-02-01
API Gravity Standards
American Petroleum Institute gravity measurement standards
Last Updated: 2026-01-15
ASTM International Standards
ASTM standards for density and specific gravity testing
Last Updated: 2026-01-20
⚠️ Disclaimer: This calculator provides theoretical estimates based on standard density and specific gravity formulas. Actual measurements may vary due to temperature, impurities, air bubbles, and measurement technique. Always use calibrated instruments and follow standard test procedures (ASTM, API) for critical applications. Not a substitute for professional laboratory analysis.
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