Specific Gravity Calculator: Calculate Density Ratio & Relative Density

Specific gravity (also known as relative density) is a fundamental concept in physics and engineering that describes the ratio of the density of a substance to the density of a reference substance, typically water. Whether you're studying material properties, fluid mechanics, or solving engineering problems, understanding specific gravity is essential. Our Specific Gravity Calculator makes it easy to calculate specific gravity using the formula: SG = ρ_substance / ρ_reference.

Specific gravity is a dimensionless quantity (it has no units) because it's a ratio of two densities. It tells you how many times denser (or less dense) a substance is compared to the reference material. A specific gravity greater than 1 means the substance is denser than the reference, while less than 1 means it's less dense.

Our Specific Gravity Calculator is designed for simplicity and accuracy:

1. Select Reference Substance: Choose a reference material (typically water at 4°C, which is the standard) or use a custom reference density
2. Enter Values: Input either the specific gravity or the substance density (leave one empty to calculate)
3. Select Units: Choose your preferred density units
4. Calculate: Click Calculate to get instant results with step-by-step solutions

The calculator uses the fundamental formula: SG = ρ_substance / ρ_reference

The specific gravity formula is straightforward:

Rearranging the Formula

You can rearrange this formula to solve for any variable:

• Substance Density: ρ_substance = SG × ρ_reference
• Reference Density: ρ_reference = ρ_substance / SG
• Specific Gravity: SG = ρ_substance / ρ_reference

The choice of reference substance is crucial for specific gravity calculations:

• Water at 4°C (Standard): Density = 1000 kg/m³ = 1 g/cm³. This is the most common reference for liquids and solids
• Water at 20°C: Density = 998.2 kg/m³. Commonly used for room temperature applications
• Water at 25°C: Density = 997.0 kg/m³. Used in laboratory settings
• Custom Reference: You can specify any reference density for specialized applications

Important: Always specify the reference substance when reporting specific gravity values, as different references will give different results.

Specific gravity calculations are used in countless real-world scenarios:

• Material Science: Identifying and characterizing materials based on density
• Geology: Determining mineral composition and rock types
• Chemistry: Analyzing solutions, mixtures, and pure substances
• Engineering: Designing structures, selecting materials, and quality control
• Food Industry: Testing product quality, detecting adulteration, and ensuring consistency
• Petroleum Industry: Analyzing crude oil, fuels, and lubricants
• Pharmaceuticals: Quality control and formulation verification
• Beverage Industry: Testing alcohol content, sugar content, and product quality
• Construction: Testing concrete, aggregates, and building materials
• Environmental Science: Analyzing water quality and pollution levels

Specific gravity is dimensionless, but density can be expressed in various units:

• kg/m³: SI unit for density, most commonly used in physics and engineering
• g/cm³: Common in chemistry and material science (equal to g/mL)
• g/mL: Frequently used in laboratory settings
• lb/ft³: Common in US engineering applications
• lb/in³: Used for very dense materials

Conversion Tips:

• 1 g/cm³ = 1 g/mL = 1000 kg/m³
• Water at 4°C: 1000 kg/m³ = 1 g/cm³ = 62.43 lb/ft³
• Since specific gravity is a ratio, the units cancel out, making it dimensionless

Example 1: Calculating Specific Gravity

What is the specific gravity of gold? (Gold density = 19,320 kg/m³, Water at 4°C = 1000 kg/m³)

Gold is 19.32 times denser than water.

Example 2: Finding Density from Specific Gravity

If a substance has a specific gravity of 0.8 relative to water at 4°C, what is its density?

Example 3: Using Different Reference Temperatures

A liquid has a density of 850 kg/m³. Calculate its specific gravity relative to water at 20°C (998.2 kg/m³).

Understanding the difference between specific gravity and density is important:

• Density: A physical property with units (kg/m³, g/cm³, etc.) that describes mass per unit volume
• Specific Gravity: A dimensionless ratio that compares a substance's density to a reference density
• Relationship: SG = ρ_substance / ρ_reference

Specific gravity is particularly useful because it's independent of the unit system used, making it easy to compare materials across different measurement systems.

Temperature significantly affects density and therefore specific gravity:

• Most substances expand when heated: Density decreases, so specific gravity decreases
• Water is unique: It reaches maximum density at 4°C, which is why this temperature is used as the standard reference
• Measurement conditions: Always specify the temperature at which specific gravity is measured
• Standard conditions: Many industries use 20°C or 25°C as standard measurement temperatures

Our calculator allows you to select different water temperatures as references to account for temperature effects.

Understanding specific gravity is fundamental to material science, fluid mechanics, and engineering. Our Specific Gravity Calculator simplifies these calculations, supporting multiple reference substances and unit conversions to make solving specific gravity problems easy and accurate.

Ready to explore more physics concepts? Check out our Density Calculator for calculating density from mass and volume, our Flow Rate Calculator for fluid mechanics, or our Reynolds Number Calculator for flow regime analysis.