Specific Gravity Calculator

Calculate the specific gravity (SG) of any material — the dimensionless ratio of its density to a reference density (water at 4°C, air, or custom). Includes mass‑volume density derivation, real‑time unit conversion, and buoyancy interpretation.

Substance Density
Example materials:
Iron (7.87 g/cm³) Water (1.00) Aluminum (2.70) Ethanol (0.789) Mercury (13.56)
Reference Density
Standard reference: pure water at 4°C (1 g/cm³ ≈ 1000 kg/m³). For gases, reference air at 20°C (≈1.204 kg/m³).
Alternative: Compute density from mass & volume
Enter mass & volume → calculates density and auto-fills substance density field (unit: g/cm³).
Local computation – No data stored or sent to servers. Unit conversions are based on standard physical constants (1 g/cm³ = 1000 kg/m³ = 62.428 lb/ft³).

What is Specific Gravity? Scientific & Practical Context

Specific gravity (SG), also known as relative density, is the ratio of the density of a substance to the density of a given reference material. For liquids and solids, the reference is almost always water at 4 °C (maximum density: 1 g/cm³ or 1000 kg/m³). For gases, air at standard conditions is often used. Because it is a ratio, SG is a dimensionless quantity — the same value regardless of unit system.

SG = ρsubstance / ρreference
where ρ = density (mass per unit volume)

This calculator supports direct density entry with smart unit conversion (g/cm³, kg/m³, lb/ft³) and also provides a mass‑volume utility to derive density on the fly — ideal for lab measurements or irregular samples.

How to Use This Calculator in a Real Laboratory Setting

  1. Measure mass – Use a precision balance (e.g., 0.001g resolution for small samples).
  2. Measure volume – For regular solids: geometric calculation; for irregular objects: water displacement (Archimedes’ method). For liquids: use a volumetric flask or pycnometer.
  3. Enter mass and volume in the “Alternative: Compute density from mass & volume” section, then click “Set density”. The substance density field will be filled automatically.
  4. Set reference density – For water-based SG, keep reference as 1.00 g/cm³. For gases, change reference to air density (e.g., 0.001225 g/cm³ at 20°C).
  5. Click “Calculate Specific Gravity” – Read the SG value and buoyancy interpretation.
Temperature note: Density varies with temperature. For high‑precision work, measure both substance and reference at the same temperature, or apply correction factors (e.g., using ASTM D1250 for petroleum).

Why Specific Gravity Matters in Real-World Applications

  • Mineralogy & Geology: Geologists identify minerals by comparing SG (e.g., gold SG ~19.3, quartz ~2.65).
  • Battery Testing: Hydrometers measure electrolyte SG to determine state of charge in lead‑acid batteries.
  • Petroleum & Fuels: API gravity is derived from SG; crucial for crude oil grading and fuel quality.
  • Plastics & Composites: Material selection for lightweight structures (SG determines buoyancy and weight).
  • Fluid Mechanics: Buoyancy, stability of ships, and sediment transport depend on SG differences.
Case Study: Lead‑Acid Battery Health Monitoring

A fully charged lead‑acid battery has electrolyte (sulfuric acid) with specific gravity of about 1.265 – 1.285 (measured at 25°C). A discharged battery drops to around 1.120 – 1.150. Using this calculator: set reference density = 1.000 (water), then enter the measured electrolyte density (e.g., 1.250 g/cm³) → SG = 1.250. According to battery standards, SG below 1.200 indicates significant discharge. This quick check helps prevent sulfation and prolong battery life.

Try it: Click the “Ethanol” example and replace the density value with 1.250 to see SG for a charged battery.

Case Study: Gemstone Identification

A gemologist measures a suspected sapphire (density ~4.00 g/cm³) and a cubic zirconia (SG ~5.65). Using water as reference (1.00 g/cm³), the specific gravity values are 4.00 and 5.65 respectively. This simple SG test provides an initial classification without destructive methods. Our calculator helps gemology students instantly verify SG and compare with reference tables.

Step‑by‑Step Calculation & Unit Conversions

Our tool follows rigorous conversion: any density unit is transformed to kg/m³ (SI base) and then the SG is computed. For example, 1 g/cm³ = 1000 kg/m³ = 62.428 lb/ft³. The reference density is similarly normalized, ensuring accurate ratio. The derived SG determines buoyancy: if SG < 1, the substance floats in water; if SG = 1, it remains suspended; if SG > 1, it sinks. For non‑water references, interpretation changes accordingly.

Common Material Specific Gravity Table

Material Specific Gravity (water=1) Typical Use / Note
Air (at 20°C) 0.001204 Reference for gases
Gasoline 0.71 – 0.77 Lighter than water
Ethanol (pure) 0.789 Alcohol density
Seawater 1.025 Higher due to salts
Concrete 2.3 – 2.5 Construction aggregate
Aluminum 2.70 Lightweight alloy
Copper 8.96 Electrical wiring
Lead 11.34 Radiation shielding
Mercury 13.56 Liquid metal, high density
Gold 19.32 Precious metal, high SG

Frequently Asked Questions

No, specific gravity is a dimensionless ratio. It remains the same regardless of whether you use metric, imperial, or any other consistent system because both numerator and denominator share the same units after conversion.

Absolutely. Set the reference density to air (≈ 0.001225 g/cm³ at 20°C) or use a custom reference. The tool will correctly compute SG relative to air, widely used in natural gas and HVAC engineering.

Density varies with temperature because materials expand or contract. Our calculator uses standard reference values (water at 4°C, unless you modify reference density). For high‑precision work, you should input densities measured at the same temperature or use correction factors.

Yes, the terms are interchangeable in most scientific contexts. Relative density is the modern preferred term, while specific gravity remains common in engineering and industry.

Yes. For solutions, the density depends on concentration and temperature. You can measure the mixture density with a hydrometer and input that value. The calculator will give you the SG relative to your chosen reference (usually water).

API gravity is a specific scale used for crude oils: API = (141.5 / SG) - 131.5 (at 60°F). This calculator does not directly convert to API, but you can use the SG output in the formula. We have a dedicated API Gravity Calculator for that purpose.
Calculation verified against NIST reference data – Unit conversions follow internationally recognized standards (1 lb/ft³ = 16.0184634 kg/m³). Density values for common materials are sourced from NIST and the Wikipedia Specific Gravity page. Last content update: April 2026.

Standards & References: This tool is built upon ASTM D792 (density of plastics by displacement), ISO 1183, and NIST SP 811 (Guide for the Use of the International System of Units). The educational content has been reviewed for factual accuracy using public domain engineering handbooks (CRC Handbook, 100th Edition). No user data is stored; calculations are performed locally in your browser.

For further reading: NIST Density Measurement Program | Wikipedia: Relative Density | Engineering Toolbox – SG of common liquids.