Density vs. Specific Weight and Specific Gravity
An introduction to density, 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 poundmass per cubic foot  lb_{m } /ft^{3}  is often used. Note that there is a difference between poundforce (lb_{f}) and poundmass (lb_{m}) . Slugs can be multiplied with 32.2 for a rough value in poundmass (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
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 ...
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/m^{2}, 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
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 
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
Basic engineering data. SIsystem, unit converters, physical constants, drawing scales and more. 
Beams and Columns
Deflection and stress in beams and columns, moment of inertia, section modulus and technical information. 
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
Properties of gases, fluids and solids. Densities, specific heats, viscosities and more. 
Mechanics
The relationships between forces, acceleration, displacement, vectors, motion, momentum, energy of objects and more. 
Statics
Forces acting on bodies at rest under equilibrium conditions  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 2propanone, dimethyl ketone and pyroacetic acid. Phase diagram included. 
Air  Density vs. Pressure and Temperature
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, pKavalues, 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, C_{6}H_{6}, 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, C_{4}H_{10}, at varying temperarure and pressure, SI and Imperial units. 
Cauchy Number
Introduction to the Cauchy Number. 
Centrifugal Pumps  Influence of Viscosity
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, Dlactic 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 SIunits. 
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, C_{2}H_{6}, 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, C_{2}H_{4}, 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, CH_{4}, 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,CH_{3}OH, at varying temperature and pressure  Imperial and SI Units. 
Methanol Freeze Protected Heat Transfer Liquids
Freezing and flash points for methanol or methyl based heattransfer 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, N_{2}, 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, O_{2}, 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. 
UTube Differential Pressure Manometers
Inclined and vertical utube 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 0370 °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.