Density vs. Specific Weight and Specific Gravity
Density is defined as mass per unit volume . Mass is a property and the SI unit for density is [ kg/m 3 ].
Density can be expressed as
ρ = m / V = 1 / ν [1]
where
ρ = density [kg/m 3 ], [slugs/ft 3 ]
m = mass [kg], [slugs]
V = volume [m 3 ], [ft 3 ]
ν = specific volume [m 3 /kg], [ft 3 /slug]
- What is weight and what is mass ? - the difference between weight and mass
The Imperial (U.S.) units for density are slugs /ft 3 but pound-mass per cubic foot - lb m /ft 3 - is often used. Note that there is a difference between pound-force (lb f ) and pound-mass (lb m ) . Slugs can be multiplied with 32.2 for a rough value in pound-mass (lb m ) .
- 1 slug = 32.174 lb m = 14.594 kg
- 1 kg = 2.2046 lb m = 6.8521x10 -2 slugs
- density of water: 1000 kg/m 3 , 1.938 slugs/ft 3
See also Unit converter - mass and Unit converter - density
On atomic level - particles are packed tighter inside a substance with higher density. Density is a physical property - constant at a given temperature and pressure - and may be helpful for identification of substances.
Below on this page: Specific gravity (relative density) , Specific gravity for gases , Specific weight , Calculation examples
Se also: Densities for some common materials
Water - Density, Specific Weight and Thermal Expantion Coefficient - variation with temperature at 1, 68 and 680 atm, SI and Imperial units
Air - Density, Specific Weight and Thermal Expantion Coefficient - variation with temperature and pressure, SI and Imperial units
How to measure density of liquid petroleum products
Example 1: Density of a Golf ball
Example 2: Using Density to Identify a Material
Example 3: Density to Calculate Volume Mass
Specific Gravity (Relative Density) - SG - is a dimensionless unit defined as the ratio of the density of a substance to the density of water - at a specified temperature and can be expressed as
SG = ρ substance / ρ H2O [2]
where
SG = Specific Gravity of the substance
ρ substance = density of the fluid or substance [kg/m 3 ]
ρ H2O = density of water - normally at temperature 4 o C [kg/m 3 ]
It is common to use the density of water at 4 o C (39 o F) as a reference since water at this point has its highest density of 1000 kg/m 3 or 1.940 slugs/ft 3 .
Since Specific Gravity - SG - is dimensionless, it has the same value in the SI system and the imperial English system (BG). SG of a fluid has the same numerical value as its density expressed in g/mL or Mg/m 3 . Water is normally also used as reference when calculating the specific gravity for solids.
See also Thermophysical Properties of Water - Density, Freezing temperature, Boiling temperature, Latent heat of melting, Latent heat of evaporation, Critical temperature ...
Example 4: Specific Gravity of Iron
Specific Gravity for some common Materials
| Substance | Specific Gravity - SG - |
|---|---|
| Acetylene | 0.0017 |
| Air, dry | 0.0013 |
| Alcohol | 0.82 |
| Aluminum | 2.72 |
| Brass | 8.48 |
| Cadmium | 8.57 |
| Chromium | 7.03 |
| Copper | 8.79 |
| Carbon dioxide | 0.00198 |
| Carbon monoxide | 0.00126 |
| Cast iron | 7.20 |
| Hydrogen | 0.00009 |
| Lead | 11.35 |
| Mercury | 13.59 |
| Nickel | 8.73 |
| Nitrogen | 0.00125 |
| Nylon | 1.12 |
| Oxygen | 0.00143 |
| Paraffin | 0.80 |
| Petrol | 0.72 |
| PVC | 1.36 |
| Rubber | 0.96 |
| Steel | 7.82 |
| Tin | 7.28 |
| Zinc | 7.12 |
| Water (4 o C) | 1.00 |
| Water, sea | 1.027 |
| Wood, Oak | 0.77 |
Specific Gravity of gases is normally calculated with reference to air - and defined as the ratio of the density of the gas to the density of the air - at a specified temperature and pressure.
The Specific Gravity can be calculated asSG = ρ gas / ρ air [3]
where
SG = specific gravity of gas
ρ gas = density of gas [kg/m 3 ]
ρ air = density of air (normally at NTP - 1.204 [kg/m 3 ])
- NTP - Normal Temperature and Pressure - defined as 20 o C (293.15 K, 68 o F) and 1 atm ( 101.325 kN/m2, 101.325 kPa, 14.7 psia, 0 psig, 30 in Hg, 760 torr)
Molecular weights can be used to calculate Specific Gravity if the densities of the gas and the air are evaluated at the same pressure and temperature.
See also Thermophysical Properties of Air - density, viscosity, critical temperature and pressure, triple point, enthalpi and entropi, thermal conductivity and diffusicity,......
Specific Weight is defined as weight per unit volume . Weight is a force . The SI unit for specific weight is [N/m 3 ]. The imperial unit is [lb/ft 3 ].
Specific Weight (or force per unit volume) can be expressed as
γ = ρ a g [4]
where
γ = specific weight (N/m 3 ], [lb/ft 3 ]
ρ = density [kg/m 3 ], [slugs/ft 3 ]
a g = acceleration of gravity (9.807 [m/s 2 ], 32.174 [ft/s 2 ] under normal conditions)
- What is weight and what is mass ? - the difference between weight and mass
Example 5: Specific Weight of Water
Specific Weight for Some common Materials
| Product | Specific Weight - γ - | |
|---|---|---|
| Imperial Units (lb/ft 3 ) | SI Units (kN/m 3 ) | |
| Aluminum | 172 | 27 |
| Brass | 540 | 84.5 |
| Carbon tetrachloride | 99.4 | 15.6 |
| Copper | 570 | 89 |
| Ethyl Alcohol | 49.3 | 7.74 |
| Gasoline | 42.5 | 6.67 |
| Glycerin | 78.6 | 12.4 |
| Kerosene | 50 | 7.9 |
| Mercury | 847 | 133.7 |
| SAE 20 Motor Oil | 57 | 8.95 |
| Seawater | 63.9 | 10.03 |
| Stainless Steel | 499 - 512 | 78 - 80 |
| Water | 62.4 | 9.81 |
| Wrought Iron | 474 - 499 | 74 - 78 |
Examples
Example 1: Density of a Golf ball
A golf ball has a diameter of 42 mm and a mass of 45 g. The volume of the golf ball can be calculated as
V = (4/3) π (42 [mm] * 0.001 [m/mm]/2) 3 = 3.8 10 -5 [m 3 ]
The density of the golf ball can then be calculated as
ρ = 45 [g] * 0.001 [kg/g] / 3.8 10 -5 [m 3 ] = 1184 [kg/m 3 ]
Example 2: Using Density to Identify a Material
An unknown liquid substance has a mass of 18.5 g and occupies a volume of 23.4 ml (milliliter).
The density of the substance can be calculated as
ρ = (18.5 [g] /1000 [g/kg]) / (23.4 [ml] /(1000 [ml/l] * 1000[l/m 3 ]))
= 18.5 10 -3 [kg] /23.4 10 -6 [m 3 ] = 790 [kg/m 3 ]
If we look up the densities of some common liquids we find that ethyl alcohol - or ethanol - has a density of 789 kg/m 3 . The liquid may be ethyl alcohol!
Example 3: Density to Calculate Volume Mass
The density of titanium is 4507 kg/m 3 . The mass of 0.17 m 3 volume titanium can be calculated as
m = 0.17 [m 3 ] * 4507 [kg/m 3 ] = 766.2 [kg]
Note! - be aware that there is a difference between " bulk density" and actual "solid or material density". This may not be clear in the description of products. Always double check values with other sources before important calculations.
Example 4: Specific Gravity of Iron
The density of iron is 7850 kg/m 3 . The specific gravity of iron related to water with density 1000 kg/m 3 is
SG(iron) = 7850 [kg/m 3 ] / 1000 [kg/m 3 ] = 7.85
Example 5: Specific Weight of Water
The density of water is 1000 kg/m3 at 4 °C (39 °F).
The specific weight in SI units is
γ = 1000 [kg/m 3 ] * 9.81 [m/s 2 ] = 9810 [N/m 3 ] = 9.81 [kN/m 3 ]
The density of water is 1.940 slugs/ft3 at 39 °F (4 °C).
The specific weight in Imperial units is
γ = 1.940 [slugs/ft 3 ] * 32.174 [ft/s 2 ] = 62.4 [lb/ft 3 ]
Related Topics
• Basics
The SI-system, unit converters, physical constants, drawing scales and more.
• Beams and Columns
Deflection and stress, moment of inertia, section modulus and technical information of beams and columns.
• Densities
Densities of solids, liquids and gases. Definitions and convertion calculators.
• Fluid Mechanics
The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.
• Material Properties
Material properties of gases, fluids and solids - densities, specific heats, viscosities and more.
• Mechanics
Forces, acceleration, displacement, vectors, motion, momentum, energy of objects and more.
• Statics
Loads - forces and torque, beams and columns.
Related Documents
Acceleration of Gravity and Newton's Second Law
Acceleration of gravity and Newton's Second Law - SI and Imperial units.
Acceleration Units Converter
Converting between units of acceleration.
Acetone - Density and Specific Weight
Online calculator, figures and tables showing density and specific weight of acetone at temperatures ranging from -95 to 275 °C (-138 to 530 °F) at atmospheric and higher pressure - Imperial and SI Units.
Acetone - Thermophysical Properties
Chemical, physical and thermal properties of acetone, also called 2-propanone, dimethyl ketone and pyroacetic acid. Phase diagram included.
Air - Density vs. Pressure and Temperatures
Air density at pressure ranging 1 to 10 000 bara (14.5 - 145000 psi) and constant selected temperatures.
Alcohols and Carboxylic Acids - Physical Data
Molweight, melting and boiling point, density, pKa-values, as well as number of carbon and hydrogen atoms in molecules are given for 150 different alcohols and acids.
Ammonia Gas - Density vs. Temperature and Pressure
Online calculator with figures and tables showing density and specific weight of ammonia for temperatures ranging -50 to 425 °C (-50 to 800 °F) at atmospheric and higher pressure - Imperial and SI Units.
Argon - Density and Specific Weight
Online calculator, figures and tables showing density and specific weight of argon, Ar, at varying temperature and pressure - Imperial and SI Units.
Baume's Hydrometer
Liquid density with Degree Baume vs. Specific Gravity.
Benzene - Density and Specific Weight vs. Temperature and Pressure
Online calculator, figures and table showing density and specific weight of benzene, C6H6, at temperatures ranging from 5 to 325 °C (42 to 620 °F) at atmospheric and higher pressure - Imperial and SI Units.
Benzene - Thermophysical properties
Chemical, physical and thermal properties of benzene, also called benzol. Phase diagram included.
Butane - Density and Specific Weight vs. Temperature and Pressure
Online calculators, figures and tables showing density and specific weight of liquid and gaseous butane, C4H10, at varying temperarure and pressure, SI and Imperial units.
Cauchy Number
Introduction to the Cauchy Number.
Centrifugal Pumps - Viscosity Influence
Hydrodynamic losses through pumps depends on fluid viscosities.
Compression and Expansion of Gases
Isothermal and isentropic gas compression and expansion processes.
Crude Oil - Density vs. Temperature
Variations in crude oil density are shown as function of temperatur, together with volume correction factors.
Crude Oil Viscosity vs. Gravity
Viscosity at 20°C/68°F and 50°C/122°F for more than 120 crudes is shown as function of specific gravity@15°C/60°F.
Densities of Aqueous Solutions of Inorganic Chlorides
Changes in density of aqueous solutions with changes in concentration at 20°C. Density of inorganic chlorides in water is plotted as function of wt%, mol/kg water and mol/l solution.
Densities of Aqueous Solutions of Inorganic Potassium Salts
Changes in density of aqueous solutions with changes in concentration at 20°C. Density of potassium salts in water is plotted as function of wt%, mol/kg water and mol/l solution.
Densities of Aqueous Solutions of Inorganic Sodium Salts
Changes in density of aqueous solutions with changes in concentration at 20°C. Density of inorganic sodium salts in water is plotted as function of wt%, mol/kg water and mol/l solution.
Densities of Aqueous Solutions of Organic Acids
Changes in density of aqueous solutions with changes in concentration at 20°C. Density of acetic acid, citric acid, formic acid, D-lactic acid, oxalic acid and trichloroacetic acid in water is plotted as function of wt%, mol/kg water and mol/l solution.
Densities of common Products
Densities of common products - Imperial and SI-units.
Density Converter
Online density converter with commonly used units.
Density of Aqueous Solutions of Organic Substances as Sugars and Alcohols
Changes in density of aqueous solutions with changes in concentration at 20°C. Density of some sugars, alcohols and other organic substances in water is plotted as function of wt%, mol/kg water and mol/l solution.
Density of Aqueous Solutions of some Inorganic Substances
Changes in density of aqueous solutions with changes in concentration at 20°C. Density of inorganic substances in water is plotted as function of wt%, mol/kg water and mol/l solution.
Dirt and Mud - Densities
Densities - pound per cubic foot and kilograms per cubic metre - of dirt and mud.
Ditch Filling Materials - Densities
Weight or density of ditch filling materials.
Energy Equation - Pressure Loss vs. Head Loss
Calculate pressure loss - or head loss - in ducts, pipes or tubes.
Engineering Materials - Properties
Some typical properties of engineering materials like steel, plastics, ceramics and composites.
Ethane - Density and Specific Weight vs. Temperature and Pressure
Online calculator, figures and tables showing density and specific weight of ethane, C2H6, at varying temperature and pressure - Imperial and SI Units.
Ethylene - Density and Specific Weight vs. Temperature and Pressure
Online calculator, figures and tables showing density and specific weight of ethylene, C2H4, at varying temperature and pressure - Imperial and SI Units.
Ethylene - Thermophysical Properties
Chemical, physical and thermal properties of ethylene, also called ethene, acetene and olefiant gas. Phase diagram included.
Fuel Oils - Densities vs. Temperature
Variations in fuel oils density as function of temperatur, together with volume correction factors.
Fuels - Densities and Specific Volumes
Densities and specific volumes fuels like anthracite, butane, gasoil, diesel, coke, oil, wood and more.
Gases - Specific Gravities
Specific gravities of air, ammonia, butadiene, carbon dioxide, carbon monoxide and some other common gases.
Gravity Heating System
The density difference between hot and cold water is the circulating force in a self circulating gravity heating system.
Heavy Water - Thermophysical Properties
Thermodynamic properties of heavy water (D2O) like density, melting temperature, boiling temperature, latent heat of fusion, latent heat of evaporation, critical temperature and more.
Helium - Density and Specific Weight vs. Temperature and Pressure
Online calculator, figures and tables showing density and specific weight of helium, He, at varying temperature and pressure - Imperial and SI Units.
Hydrocarbon Mixtures - Average Boiling Points vs. Gravity and Molecular Weights
Formulas and examples of calculation of boiling point of hydrocarbon mixtures from gravity and molecular weight.
Hydrocarbon Mixtures - Molecular Weight vs. Gravity and Average Boiling Point
Formulas and examples of calculation of average molecular weight of hydrocarbon mixtures from gravity and average boiling point, achieved from distillation data.
Hydrocarbons - Physical Data
Molweight, melting and boiling point, density, flash point and autoignition temperature, as well as number of carbon and hydrogen atoms in each molecule for 200 different hydrocarbons.
Hydrocarbons, Linear Alcohols and Acids - Densities
Density of hydrocarbons like alcohols and acids as function of carbon number at 20°C / 68°.
International Standard Atmosphere
International standard atmosphere in elevation -2000 to 30000 metre - pressure, temperature, density, viscosity, thermal conductivity and velocity of sound.
Jet Fuel - Density vs. Temperature
Variations in jet fuel density as function of temperatur, together with volume correction factors.
Levers
Use levers to magnify forces.
Liquids - Densities vs. Pressure and Temperature Change
Densities and specific volume of liquids vs. pressure and temperature change.
Liquids - Specific Gravities
Specific gravities of liquids like alcohol, oils, benzene, water and many more.
Liquids - Specific Gravities
Specific gravities for common fluids like acetone, alcohol, turpentine, oil and more.
Lubricating Oil - Densities vs. Temperature
Variations in lubricating oil density as function of temperatur, together with volume correction factors.
Mach Number
An introduction to the Mach Number.
Mass vs. Weight
Mass vs. weight - the Gravity Force.
Mercury - Thermodynamic Properties
Properties of saturated liquid Mercury - Hg - density, specific heat capacity, kinematic viscosity, thermal conductivity and Prandtl number.
Methane - Density and Specific Weight vs. Temperature and Pressure
Online calculator, figures and tables showing density and specific weight of methane, CH4, at temperatures ranging from -160 to 725 °C (-260 to 1300 °F) at atmospheric and higher pressure - Imperial and SI Units.
Methanol - Density and Specific Weight vs. Temperature and Pressure
Online calculator, figures and tables showing density and specific weight of methanol,CH3OH, at varying temperature and pressure - Imperial and SI Units.
Methanol Freeze Protected Heat Transfer Liquids
Freezing and flash points for methanol or methyl based heat-transfer fluids or brines.
Minerals and other Materials - Specific Gravities
Specific gravities for minerals and other materials.
Natural Gas - Pipe Sizing Calculator
Calculate capacities and dimensions of natural gas pipe lines.
Nitrogen - Density and Specific Weight vs. Temperature and Pressure
Online calculator, figures and tables showing density and specific weight of nitrogen, N2, at temperatures ranging from -175 to 1325 °C (-280 to 2400 °F) at atmospheric and higher pressure - Imperial and SI Units.
Nitrogen - Thermal Diffusivity vs. Temperature and Pressure
Figures and tables showing thermal diffusivity of nitrogen at varying temperarure and pressure, SI and Imperial units.
Organic Sulfur Compounds - Densities
Liquid density of different kinds of organic sulfur compounds with varying carbon number (20°C/68°F). Comparison of thiols, sulfides, disulfides and thiophenes.
Ounces and Pounds vs. Grams
Converting ounces (ozs.) and pounds (lbs.) to grams (g).
Oxygen - Density and Specific Weight vs. Temperature and Pressure
Online calculator, figures and tables showing density and specific weight of oxygen, O2, at varying temperature and pressure - Imperial and SI Units.
Pentane - Density and Specific Weight vs. Temperature and Pressure
Online calculator, figures and table showing density and specific weight of pentane, C5H12, at temperatures ranging from -130 to 325 °C (-200 to 620 °F) at atmospheric and higher pressure - Imperial and SI Units.
Pitot Tubes
Pitot tubes can be used to measure fluid flow velocities by measuring the difference between static and dynamic pressure in the flow.
Porosity
Volume not occupied by solid material.
Propane - Density and Specific Weight vs. Temperature and Pressure
Online calculator, figures and tables showing density and specific weight of propane, C3H8, at temperatures ranging from -187 to 725 °C (-305 to 1300 °F) at atmospheric and higher pressure - Imperial and SI Units.
Pumps, Fans and Turbines - Horsepower
British Horse Power as used for pumps, fans and turbines - and how to convert to other units.
Solids - Densities
Densities of selected solids.
Solids and Metals - Specific Gravities
Specific gravity for common solids and metals like aluminum, asbestos, brass, calcium and many others.
STP - Standard Temperature and Pressure and NTP - Normal Temperature and Pressure
The definition of STP - Standard Temperature and Pressure and NTP - Normal Temperature and Pressure.
Sugar Solubility in Water
Solubility of sugar in water.
The Ideal Gas Law
The relationship between volume, pressure, temperature and quantity of a gas, including definition of gas density.
Thermoplastics - Physical Properties
Physical properties of thermoplastics like ABS, PVC, CPVC, PE, PEX, PB and PVDF.
Toluene - Density and Specific Weight vs. Teemperature and Pressure
Density and specific weight of liquid toluene.
Total and Partial Pressure - Dalton's Law of Partial Pressures
How to calculate total pressure and partial pressures for gas mixtures from Ideal Gas Law.
Troy Weight
Weight unit for preciuos metals like gold and silver.
U-Tube Differential Pressure Manometers
Inclined and vertical u-tube manometers used to measure differential pressure in flow meters like pitot tubes, orifices and nozzles.
Unit Converter with commonly used Units
Common converting units for Acceleration, Area, Density, Energy, Energy per unit mass, Force, Heat flow rate, Heat flux, Heat generation per unit volume and many more.
Universal Gravitational Law
Gravitational attraction between two objects vs. mass of the objects and the distance between them.
Water - Specific Volume vs. Temperature
Online calculator, figures and tables showing Specific Volume of water at temperatures ranging from 0-370 °C and 32 - 700 °F - Imperial and IS Units.
Water - Thermophysical Properties
Thermal properties of water at different temperatures like density, freezing temperature, boiling temperature, latent heat of melting, latent heat of evaporation, critical temperature and more.
Wood Species - Densities
Densities of various wood species - apple, ash, cedar, elm and more.
Yield Structure of Crude Oils with Increasing Density of Crude
Yields of different crude oil distillation cuts are plotted as function of whole crude specific gravity. Fractions based on European and North American markets, and the typical differences in crude oil fractionation in the two markets are also shown.