Viscosity  Absolute (Dynamic) vs. Kinematic
Vicosity is a fluid's resistance to flow and can be valued as dynamic (absolute) or kinematic.
Viscosity is an important fluid property when analyzing liquid behavior and fluid motion near solid boundaries. The viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress. The shear resistance in a fluid is caused by intermolecular friction exerted when layers of fluid attempt to slide by one another.
 viscosity is the measure of a fluid's resistance to flow
 molasses is highly viscous
 water is medium viscous
 gas is low viscous
There are two related measures of fluid viscosity
 dynamic ( or absolute )
 kinematic
Dynamic (absolute) Viscosity
Absolute viscosity  coefficient of absolute viscosity  is a measure of internal resistance. Dynamic (absolute) viscosity is the tangential force per unit area required to move one horizontal plane with respect to an other plane  at an unit velocity  when maintaining an unit distance apart in the fluid.
The shearing stress between the layers of a non turbulent fluid moving in straight parallel lines can be defined for a Newtonian fluid as
Shear stress can be expressed
τ = μ dc / dy
= μ γ (1)
where
τ = shearing stress in fluid (N/m^{2})
μ = dynamic viscosity of fluid (N s/m^{2})
dc = unit velocity (m/s)
dy = unit distance between layers (m)
γ = dc / dy = shear rate (s^{1} )
Equation (1) is known as the Newtons Law of Friction.
(1) can be rearranged to express Dynamic viscosity as
μ = τ dy / dc
= τ / γ (1b)
In the SI system the dynamic viscosity units are N s/m^{2}, Pa s or kg/(m s)  where
 1 Pa s = 1 N s/m^{2}= 1 kg/(m s) = 0.67197 lb_{m} /(ft s) = 0.02088 slug /(ft s) = 0.02089 lb_{f} s/ft^{2}
Dynamic viscosity may also be expressed in the metric CGS (centimetergramsecond) system as g/(cm s) , dyne s/cm ^{ 2 } or poise (p) where
 1 poise = 1 dyne s/cm^{2}= 1 g/(cm s) = 1/10 Pa s = 1/10 N s/m^{2}
For practical use the Poise is normally too large and the unit is therefore often divided by 100  into the smaller unit centipoise (cP)  where
 1 P = 100 cP
 1 cP = 0.01 poise = 0.01 gram per cm second = 0.001 Pascal second = 1 milliPascal second = 0.001 N s/m^{2}
Water at 20.2 ^{o}C (68.4 ^{o}F) has the absolute viscosity of one  1  centiPoise .
Liquid  Absolute Viscosity ^{ *) } ( N s/m^{2}, Pa s) 

Air  1.983 10 ^{ 5 } 
Water  10^{3} 
Olive Oil  10^{1} 
Glycerol  10 ^{ 0 } 
Liquid Honey  10 ^{ 1 } 
Golden Syrup  10^{2} 
Glass  10 ^{ 40 } 
*) at room temperature
Kinematic Viscosity
Kinematic viscosity is the ratio of  absolute (or dynamic) viscosity to density  a quantity in which no force is involved. Kinematic viscosity can be obtained by dividing the absolute viscosity of a fluid with the fluid mass density like
ν = μ / ρ (2)
where
ν = kinematic viscosity (m^{2}/s)
μ = absolute or dynamic viscosity (N s/m^{2})
ρ = density (kg/m^{3} )
In the SIsystem the theoretical unit of kinematic viscosity is m^{2}/s  or the commonly used Stoke (St) where
 1 St (Stokes) = 10^{4} m^{2}/s = 1 cm^{2}/s
Stoke comes from the CGS (Centimetre Gram Second) unit system.
Since the Stoke is a large unit it is often divided by 100 into the smaller unit centiStoke (cSt)  where
 1 St = 100 cSt
 1 cSt (centiStoke) = 10^{6} m^{2}/s = 1 mm^{2}/s
 1 m^{2}/s = 10^{6} centiStokes
The specific gravity for water at 20.2 ^{o}C (68.4 ^{o}F) is almost one, and the kinematic viscosity for water at 20.2 ^{o}C (68.4 ^{o}F) is for practical purpose 1.0 mm^{2}/s ( cStokes). A more exact kinematic viscosity for water at 20.2 ^{o}C (68.4 ^{o}F) is 1.0038 mm^{2}/s (cSt).
A conversion from absolute to kinematic viscosity in Imperial units can be expressed as
ν = 6.7197 10^{4} μ / γ (2a)
where
ν = kinematic viscosity (ft^{2}/s)
μ = absolute or dynamic viscosity (cP)
γ = specific weight (lb/ft^{3} )
Viscosity and Reference Temperature
The viscosity of a fluid is highly temperature dependent  and for dynamic or kinematic viscosity to be meaningful the reference temperature must be quoted. In ISO 8217 the reference temperature for a residual fluid is 100 ^{o}C . For a distillate fluid the reference temperature is 40 ^{o}C .
 for a liquid  the kinematic viscosity decreases with higher temperature
 for a gas  the kinematic viscosity increases with higher temperature
Related Mobile Apps from The Engineering ToolBox
This is a free app that can be used offline on mobile devices.
Other Viscosity Units
Saybolt Universal Seconds (or SUS, SSU )
Saybolt Universal Seconds (or SUS ) is an alternative unit for measuring viscosity. The efflux time is Saybolt Universal Seconds ( SUS ) required for 60 milliliters of a petroleum product to flow through the calibrated orifice of a Saybolt Universal viscometer  under a carefully controlled temperature and as prescribed by test method ASTM D 88. This method has largely been replaced by the kinematic viscosity method. Saybolt Universal Seconds is also called the SSU number (Seconds Saybolt Universal) or SSF number (Saybolt Seconds Furol) .
Kinematic viscosity in SSU versus dynamic or absolute viscosity can be expressed as
ν _{ SSU } = B μ / SG
= B ν _{ centiStokes }(3)
where
ν _{ SSU } = kinematic viscosity (SSU)
B = 4.632 for temperature 100 ^{o}F (37.8 ^{o}C)
B = 4.664 for temperature 210 ^{o}F (98.9 ^{o}C)
μ = dynamic or absolute viscosity (cP)
SG = Specific Gravity
ν _{ centiStokes } = kinematic viscosity (centiStokes)
Degree Engler
Degree Engler is used in Great Britain as a scale to measure kinematic viscosity. Unlike the Saybolt and Redwood scales, the Engler scale is based on comparing the flow of the substance being tested to the flow of another substance  water. Viscosity in Engler degrees is the ratio of the time of a flow of 200 cubic centimeters of the fluid whose viscosity is being measured  to the time of flow of 200 cubic centimeters of water at the same temperature (usually 20 ^{o}C but sometimes 50 ^{o}C or 100 ^{o}C ) in a standardized Engler viscosity meter.
Newtonian Fluids
A fluid where the shearing stress is linearly related to the rate of shearing strain  is designated as a Newtonian Fluid.
A Newtonian material is referred to as true liquid since the viscosity or consistency is not affected by shear such as agitation or pumping at a constant temperature. Most common fluids  both liquids and gases  are Newtonian fluids. Water and oils are examples of Newtonian liquids.
Shearthinning or Pseudoplastic Fluids
A Shearthinning or pseudoplastic fluid is a fluid where the viscosity decrease with increased shear rate. The structure is timeindependent.
Thixotropic Fluids
A Thixotropic fluid has a timedependent structure. The viscosity of a thixotropic fluid decreases with increasing time  at a constant shear rate.
Ketchup and mayonnaise are examples of thixotropic materials. They appear thick or viscous but are possible to pump quite easily.
Dilatant Fluids
A Shear Thickening Fluid  or Dilatant Fluid  increases the viscosity with agitation or shear strain. Dilatant fluids are known as nonNewton fluids.
Some dilatant fluids can become almost solid in a pump or pipe line. With agitation cream becomes butter and candy compounds. Clay slurry and similar heavily filled liquids do the same thing.
Bingham Plastic Fluids
A Bingham Plastic Fluid has a yield value which must be exceeded before it will start to flow like a fluid. From that point the viscosity decreases with increasing agitation. Toothpaste, mayonnaise and tomato ketchup are examples of such products.
Example  Air, Convert between Kinematic and Absolute Viscosity
Kinematic viscosity of air at 1 bar (1 10^{5} Pa, N/m^{2}) and 40 ^{o}C is 16.97 cSt (16.97 10^{6} m^{2}/s) .
The density of the air can be estimated with the Ideal Gas Law
ρ = p / (R T)
= (1 10^{5} N/m^{2}) / ( (287 J/(kg K)) ((273 ^{o}C) + (33 ^{o}C)) )
= 1.113 (kg/m^{3} )
where
ρ = density (kg/m^{3} )
p = absolute pressure (Pa, N/m^{2})
R = individual gas constant (J/(kg K))
T = absolute temperature (K)
The absolute viscosity can be calculated as
μ = 1.113 (kg/m^{3} ) 16.97 10^{6} (m^{2}/s)
= 1.88 10 ^{ 5 } (kg/(m s), N s/m^{2})
Viscosity of some Common Liquids
centiStokes (cSt, 10^{6} m^{2}/s, mm^{2}/s )  Saybolt Second Universal (SSU, SUS)  Typical liquid 

0.1  Mercury  
1  31  Water (20 ^{o}C) 
4.3  40  Milk SAE 20 Crankcase Oil SAE 75 Gear Oil 
15.7  80  No. 4 fuel oil 
20.6  100  Cream 
43.2  200  Vegetable oil 
110  500  SAE 30 Crankcase Oil SAE 85 Gear Oil 
220  1000  Tomato Juice SAE 50 Crankcase Oil SAE 90 Gear Oil 
440  2000  SAE 140 Gear Oil 
1100  5000  Glycerine (20 ^{o}C) SAE 250 Gear Oil 
2200  10000  Honey 
6250  28000  Mayonnaise 
19000  86000  Sour cream 
Kinematic viscosity can be converted from SSU to Centistokes with
ν _{ Centistokes } = 0.226 ν _{ SSU }  195 / ν _{ SSU } (4)
where
ν _{ SSU } < 100
ν _{ Centistokes } = 0.220 ν _{ SSU }  135 / ν _{ SSU }
where
ν _{ SSU } > 100
Viscosity and Temperature
Kinematic viscosity of fluids like water, mercury, oils SAE 10 and oil no. 3  and gases like air, hydrogen and helium are indicated in the diagram below. Note that
 for liquids  viscosity decreases with temperature
 for gases  viscosity increases with temperature
Measuring Viscosity
Three types of devices are used to measure viscosity
 capillary tube viscometer
 Saybolt viscometer
 rotating viscometer
Related Topics

Fluid Flow and Pressure Loss in Pipes and Tubes
Fluid flow and pressure loss in pipe lines. Water and sewer systems. Steel pipes, pvc pipes, copper tubes and more. 
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. 
Pumps
Design of pumping systems and pipelines. With centrifugal pumps, displacement pumps, cavitation, fluid viscosity, head and pressure, power consumption and more. 
Viscosities
Viscosities of products and chemical species at varying conditions.
Related Documents

Absolute or Dynamic Viscosity Online Converter
Convert between dynamic or absolute viscosity units  Poiseuille, Poise, centPoise and more. 
Acetone  Thermophysical Properties
Chemical, physical and thermal properties of acetone, also called 2propanone, dimethyl ketone and pyroacetic acid. Phase diagram included. 
Air  Dynamic and Kinematic Viscosity
Online calculator, figures and tables with dynamic (absolute) and kinematic viscosity for air at temperatures ranging 100 to 1600°C (150 to 2900°F) and at pressures ranging 1 to 10 000 bara (14.5  145000 psia)  SI and Imperial Units. 
Air  Thermophysical Properties
Thermal properties of air at different temperatures  density, viscosity, critical temperature and pressure, triple point, enthalpi and entropi, thermal conductivity and diffusivity and more. 
Ammonia  Dynamic and Kinematic Viscosity vs. Temperature and Pressure
Online calculator, figures and tables showing dynamic (absolute) and kinematic viscosity of gasous and liquid ammonia at temperatures ranging from 73 to 425°C (100 to 800°F) at pressure ranging from 1 to 1000 bara (14.5  14500 psia)  SI and Imperial Units. 
Ammonia  Prandtl Number vs. Temperature and Pressure
Figures and table with changes in Prandtl number for ammonia with changes in temperature and pressure. 
Benzene  Dynamic and Kinematic Viscosity vs. Temperature and Pressure
Online calculator, figures and table showing dynamic and kinematic viscosity of benzene, C_{6}H_{6}, at varying temperature and pressure  Imperial and SI Units. 
Benzene  Thermophysical properties
Chemical, physical and thermal properties of benzene, also called benzol. Phase diagram included. 
Butane  Dynamic and Kinematic Viscosity vs. Temperature and Pressure
Online calculators, figures and tables with dynamic and kinematic viscosity of liquid and gaseous butane, C_{4}H_{10}, at varying temperarure and pressure, SI and Imperial units. 
Centrifugal Pumps  Influence of Viscosity
Hydrodynamic losses through pumps depends on fluid viscosities. 
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. 
Dynamic (Absolute) Viscosity  Converting Chart
Convert dynamic viscosity values between units like Poiseuille  Poise  centiPoise and more. 
Energy Equation  Pressure Loss vs. Head Loss
Calculate pressure loss  or head loss  in ducts, pipes or tubes. 
Engine & Gear Oil  Recommended Viscosity vs. Outside Temperature
Oil viscosity vs. temperature. 
Ethanol  Dynamic and Kinematic Viscosity vs. Temperature and Pressure
Online calculator, figures and tables showing dynamic and kinematic viscosity of ethanol, C_{2}H_{5}OH, at varying temperature and pressure  Imperial and SI Units. 
Ethylene  Dynamic and Kinematic Viscosity vs. Temperature and Pressure
Online calculator, figures and tables showing dynamic and kinematic viscosity of ethylene, C_{2}H_{4}, also called ethene or acetene, 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. 
Food Products  Viscosities
Absolute (dynamic) viscosity for common food products. 
Gases  Dynamic Viscosities
Absolute (dynamic) viscosities of some common gases. 
HazenWilliams Pressure Loss Equation
The HazenWilliams equation can be used to calculate the pressure drop (psi) or friction loss in pipes or tubes. 
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. 
Industrial Lubricants  Viscosities vs. ISOVG Grade
ISOVG viscosity grades for industrial lubricants. 
International Standard Atmosphere
International standard atmosphere in elevation 2000 to 30000 metre  pressure, temperature, density, viscosity, thermal conductivity and velocity of sound. 
ISO Grade Oils  Viscosities and Densities
Viscosities and densities of ISO  and equivalent SAE grade oils. 
Kinematic Viscosity  Online Converter
Convert between kinematic viscosity units like centistokes, poise, lentor and more. 
Kinematic Viscosity  Unit Converter
Convert between Centistokes, Saybolt and Redwood seconds. 
Liquids  Dynamic Viscosities
Absolute (dynamic) viscosity values for some common fluids. 
Liquids  Kinematic Viscosities
Kinematic viscosities of some common liquids like motor oil, diesel fuel, peanut oil and many more. 
Methane  Dynamic and Kinematic Viscosity vs. Temperature and Pressure
Online calculator, figures and tables showing dynamic and kinematic viscosity of methane, CH_{4}, at varying temperature and pressure  Imperial and SI Units. 
Methane  Prandtl number vs. Temperature
Figures and table showing changes in Prandtl number for methane with changes in temperature and pressure. 
Methanol  Dynamic and Kinematic Viscosity vs. Temperature and Pressure
Online calculator, figures and tables showing dynamic and kinematic viscosity of liquid methanol,CH_{3}OH, at varying temperature  Imperial and SI Units. 
Motor Oils  Dynamic Viscosities
Dynamic viscosities for motor oils SAE 10 to 50 for temperatures ranging 0100 ^{o}C. 
Nitrogen  Prandtl number vs. Temperature and Pressure
Figures and tables showing Prandtl number of nitrogen at varying temperarure and pressure, SI and Imperial units. 
Oil Fuels  Viscosities vs. Temperatures
Viscosities of fuel oils vs. temperature. 
Oil Pipes  Pressure Loss vs. Oil Flow
Pressure drop in oil pipes  viscosities ranging 100  600 Saybolt Universal Seconds. 
Oil Viscosity Converter
Convert between commonly used oil viscosity units. 
Oxygen  Dynamic and Kinematic Viscosity vs. Temperature and Pressure
Online calculator, figures and tables showing dynamic and kinematic viscosity of oxygen, O_{2}, at varying temperature and pressure  Imperial and SI Units. 
Pipes Submerged in Oil or Fat  Heat Emission
Heat emission from steam or water heating pipes submerged in oil or fat  forced and natural circulation. 
Poiseuille's Formula
Calculate the volume flow discharged through a smoothwalled circular pipe. 
Propane  Dynamic and Kinematic Viscosity vs. Temperature and Pressure
Online calculators, figures and tables showing dynamic and kinematic viscosity of liquid and gaseous propane at varying temperarure and pressure, SI and Imperial units. 
Propane  Prandtl Number vs. Temperature and Pressure
Figures and tables with Prandtl Number of liquid and gaseous propane at varying temperarure and pressure, SI and Imperial units. 
Reynolds Number
Introduction and definition of the dimensionless Reynolds Number  online calculators. 
SAE Multigrade Oils  Viscosities and Densities
Viscosities and densities of SAE Grade oils. 
Seawater  Properties
Seawater properties like density, saturation pressure, specific heat, electrical conductivity and absolute viscosity. 
Secondary Coolants  Properties
Comparing properties like specific gravity, freezing points and viscosity for secondary coolants like calcium chloride, sodium chloride, ethylene glycol and propylene glycol. 
Steam  Viscosity vs. Pressure
Absolute viscosity of steam at pressure ranging 1  10000 psia. 
Steel Pipes  Viscous Liquid Flow and Friction Loss
Friction loss in schedule 40 steel pipe with viscous liquids  viscosities ranging from water to oil. 
Sugar Water Solutions  Viscosities
Dynamic viscosities of sucrose water solutions vs. temperature. 
Viscosity Converting Chart
Convert between viscosity units like Centiposes, milliPascal, CentiStokes and SSU. 
Viscous Liquids  Friction Loss vs. Viscosity and Flow
Friction loss in steel pipes for fluids with viscosities ranging 32  80000 SSU. 
Viscous Liquids  Max. Delivery Flow Velocities
Recommended max. flow velocities on delivery sides of pumps in viscous systems. 
Viscous Liquids  Max. Suction Flow Velocities
Recommended max. pump suction flow velocity for viscous fluids. 
Water  Absolute (Dynamic) Viscosity vs. Temperature and Pressure
Absolute viscosity for water in centipoises for temperatures between 32  200^{o}F. 
Water  Dynamic (Absolute) and Kinematic Viscosity vs. Temperature and Pressure
Free online calculator  figures and tables with viscosity of water at temperatures ranging 0 to 360°C (32 to 675°F)  Imperial and SI Units.