2026-07-30 8 min

Kinematic Viscosity Calculator

Convert between dynamic and kinematic viscosity. Calculate kinematic viscosity for lubricant selection and pipeline flow analysis.

Calculator

Unit System

Dynamic Viscosity mu (Pa-s)

Fluid Density (kg/m3)

Results

Normal

Kinematic Viscosity

100.00mm2/s (cSt)

Kinematic viscosity from dynamic viscosity and density

Kinematic Viscosity (SI)

0.00010000m2/s

Kinematic viscosity in SI units

Kinematic Viscosity (SUS)

466.7SUS

Saybolt Universal Seconds equivalent

Dynamic Viscosity mu

0.0875Pa-s

Input dynamic viscosity

Density

875.0kg/m3

Input fluid density

Visualizations

Results Overview

100mm2/s (cSt)Kinematic Viscosity

0mm2/s (cSt)Kinematic Viscosity

466.7mm2/s (cSt)Kinematic Viscosity

0.1mm2/s (cSt)Dynamic Viscosity mu

875mm2/s (cSt)Density

Formula

Kinematic viscosity is the ratio of dynamic viscosity to fluid density, representing the fluid resistance to flow under gravity.

nu = mu / rho

Alternative Form

mu = nu x rho

Variables

Symbol	Name	Unit	Description
nu	Kinematic Viscosity	m2/s, cSt	Ratio of dynamic viscosity to density
mu	Dynamic Viscosity	Pa-s, cP	Absolute viscosity
rho	Density	kg/m3	Mass per unit volume

Explanation

Kinematic viscosity represents the momentum diffusivity of a fluid - how quickly momentum diffuses through the fluid due to viscous effects. It appears naturally in the Navier-Stokes equations and is the viscosity measure used for Reynolds number calculations.

Derivation

From Newton law of viscosity, the shear stress tau = mu x du/dy. Dividing by density gives the kinematic viscosity nu = mu/rho, which has units of m2/s.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Measure or determine dynamic viscosity mu (Pa-s or cP).

Dynamic Viscosity mu:0.0875 Pa-s

Result: mu = 0.0875 Pa-s

Step 2

Measure or determine the fluid density rho at the same temperature.

Density rho:875.0 kg/m3

Result: rho = 875.0 kg/m3

Step 3

Apply the conversion formula: nu = mu / rho.

nu = mu / rho

mu:0.0875 Pa-s

rho:875.0 kg/m3

Intermediate: nu = 0.0875 / 875.0

Result: nu = 0.00010000 m2/s = 100.00 cSt

Final Answer

100.00

Worked Examples

See how the calculator works with different scenarios.

Scenario

An ISO VG 100 gear oil has mu = 0.0875 Pa-s at 40C and density rho = 875 kg/m3.

Inputs

Dynamic Viscosity mu:0.0875 Pa-s

Density rho:875 kg/m3

Calculation

nu = 0.0875 / 875 = 1.0 x 10^-4 m2/s = 100 cSt

Result

nu = 100 cSt (ISO VG 100)

Interpretation

This confirms the oil is correctly classified as ISO VG 100 with kinematic viscosity exactly 100 cSt at 40C.

Understanding Your Result

Your Result: Kinematic Viscosity: 100.00 mm2/s (cSt)

Typical range: Gases: 5-20 cSt. Water: 1 cSt. Hydraulic oils: 10-46 cSt. Industrial oils: 68-220 cSt. Gear oils: 320-1000 cSt. Bitumen: 10^4-10^6 cSt.

What This Means

Kinematic viscosity measures a fluid resistance to flow under gravity. It is the standard measure for lubricant classification and appears directly in the Reynolds number.

Why It Matters

Kinematic viscosity is the basis for ISO VG, SAE, and AGMA classification systems. It is the primary property reported in lubricant data sheets and used for selection, pipeline flow, and Reynolds number determination.

Professional Interpretation

Kinematic viscosity combines internal friction (dynamic viscosity) and inertia (density). Dynamic viscosity is more fundamental for lubrication engineering, but kinematic viscosity is the practical standard for specification due to capillary measurement simplicity.

Recommendations

•Use kinematic viscosity for ISO grade specification and lubricant selection
•Convert to dynamic viscosity using density for bearing and EHL film thickness calculations
•Always specify the temperature when reporting kinematic viscosity
•Track kinematic viscosity at 40C as the primary oil health indicator in condition monitoring

Educational Content

Introduction

Kinematic viscosity is the most commonly specified property of industrial lubricants. It forms the basis of the international viscosity grading system (ISO 3448).

Concept Explanation

The term kinematic emphasizes that this measure involves both internal friction (dynamic viscosity) and density. Capillary viscometers measure kinematic viscosity directly - the time for a fixed volume to flow through a calibrated capillary under gravity.

Applications

▸Lubricant ISO grade classification and selection

▸Engine oil SAE grade specification (J300)

▸Pipeline flow analysis and pressure drop calculations

▸Reynolds number determination for flow regime classification

▸Used oil analysis for condition monitoring

Benefits

•Standardized measurement method (ASTM D445) with high precision
•Basis of international lubricant classification systems
•Simple, low-cost measurement requiring minimal equipment
•Widely reported in all lubricant technical data sheets

Limitations

•Requires density for dynamic viscosity conversion
•Not directly applicable to EHL and bearing film thickness calculations
•Temperature must be precisely controlled
•Not appropriate for non-Newtonian fluids at application shear rates

Best Practices

•Always measure at precisely controlled temperatures
•Report results with the measurement temperature
•Use ASTM D445 capillary viscometers for highest accuracy
•Calibrate viscometers regularly with certified viscosity standards

Common Misconceptions

Myth: Kinematic viscosity is the intrinsic resistance to flow.

Truth: It combines dynamic viscosity and density. Two fluids with the same kinematic viscosity can have different dynamic viscosities if densities differ.

Myth: cSt and cP are the same thing.

Truth: cSt (kinematic) and cP (dynamic) are equal only when density = 1 g/cm3. For lubricants, mu(cP) = 0.85-0.9 x nu(cSt).

Myth: Kinematic viscosity alone defines lubricant performance.

Truth: VI, pressure-viscosity coefficient, additive chemistry, and thermal stability are equally important.

Practical Tips

•Kinematic viscosity by capillary viscometer is the industry standard (ASTM D445)
•1 cSt = 1 mm2/s = 10^-6 m2/s
•To convert cSt to SUS: SUS = cSt x 4.667
•ISO VG number equals midpoint kinematic viscosity at 40C
•Always verify the measurement temperature - 40C and 100C are standard

Common Mistakes

Confusing kinematic with dynamic viscosity in calculations

Reynolds number uses kinematic viscosity. Reynolds equation uses dynamic viscosity. Check formula requirements carefully.

Using density at a different temperature than viscosity

Both must be at the same temperature. A 10C mismatch causes approximately 3% error.

Neglecting non-Newtonian behavior

Kinematic viscosity measured at low shear may not represent in-service viscosity for multigrade oils and greases.

Using kinematic viscosity in EHL film thickness formulas

EHL calculations require dynamic viscosity (Pa-s) and the pressure-viscosity coefficient. Never use kinematic viscosity directly.

Assumptions

This calculator makes the following assumptions to provide estimates:

Newtonian Fluid: The fluid is assumed Newtonian with constant viscosity independent of shear rate.

Homogeneous: Single-phase liquid. Emulsions or suspensions will have different behavior.

Isothermal: Constant temperature assumed. Viscous heating can alter results in real systems.

Incompressible: Density assumed independent of pressure. At EHL pressures, density increases significantly.

Limitations

Be aware of these limitations when using this calculator:

Temperature Sensitivity: Kinematic viscosity is highly temperature-dependent. Valid only at the measurement temperature.

Pressure Effect: Does not account for viscosity increase under high pressure (piezoviscous effect).

Newtonian Assumption: Non-Newtonian fluids require apparent viscosity at the application shear rate.

Density Required for Dynamic: Dynamic viscosity requires density. Density measurement adds uncertainty.

Frequently Asked Questions

Answers to common questions about this calculator.

What is kinematic viscosity?

Kinematic viscosity (nu) is the ratio of dynamic viscosity to density: nu = mu/rho. It measures a fluid resistance to flow under gravity and has units of m2/s or cSt.

How is kinematic viscosity different from dynamic?

Dynamic viscosity (mu) measures absolute resistance to shear. Kinematic viscosity (nu) is mu divided by density. Kinematic includes density effects; dynamic does not.

What units are used for kinematic viscosity?

SI unit: m2/s. CGS unit: Stoke (St) or centistoke (cSt). 1 cSt = 1 mm2/s = 10^-6 m2/s. SUS (Saybolt Universal Seconds) is used in the US.

How do I convert dynamic to kinematic viscosity?

nu = mu / rho. If mu = 0.0875 Pa-s and rho = 875 kg/m3, then nu = 0.0875/875 = 10^-4 m2/s = 100 cSt.

What is the kinematic viscosity of water?

Water is approximately 1.0 cSt at 20C, 0.55 cSt at 50C, and 0.28 cSt at 100C.

What is the kinematic viscosity of air?

Air is approximately 15 cSt at 20C. Despite low dynamic viscosity, low density gives it kinematic viscosity comparable to light oils.

How is kinematic viscosity measured?

Capillary viscometers (ASTM D445) measure the time for a fixed volume to flow through a calibrated capillary under gravity. The efflux time multiplied by the viscometer constant gives kinematic viscosity.

What is the ISO VG classification system?

ISO 3448 classifies industrial lubricants by kinematic viscosity at 40C. Each grade is centered on a nominal viscosity: ISO VG 32, 46, 68, 100, 150, 220, 320, 460, 680, 1000, 1500.

What is the SAE engine oil classification?

SAE J300 classifies engine oils by kinematic viscosity at 100C and low-temperature CCS/MRV viscosity. Grades: 0W-8W (winter), 16-60 (high temperature). Multigrade oils like 10W-30 meet both requirements.

How does temperature affect kinematic viscosity?

Kinematic viscosity decreases exponentially with temperature. A typical mineral oil drops from 100 cSt at 40C to about 11 cSt at 100C.

What is the difference between cSt and SUS?

cSt is the SI-derived unit. SUS is an empirical US unit based on efflux time through a Saybolt viscometer. Approximate conversion: SUS = cSt x 4.667 at 100F.

Why do we need both kinematic and dynamic viscosity?

Kinematic is used for ISO grading and capillary measurement. Dynamic is needed for Reynolds equation, EHL calculations, and fundamental fluid mechanics.

How do I select lubricant viscosity grade?

Determine operating temperature, calculate required viscosity at that temperature, and select an ISO VG that provides adequate viscosity at operating conditions. Use AGMA or manufacturer recommendations.

What is the viscosity of common ISO grades at 100C?

Approximate values: ISO VG 32: 5.4 cSt, VG 46: 6.7 cSt, VG 68: 8.5 cSt, VG 100: 11 cSt, VG 150: 15 cSt, VG 220: 19 cSt, VG 320: 25 cSt, VG 460: 33 cSt at 100C.

Can kinematic viscosity be too low?

Yes. If viscosity at operating temperature is too low, the lubricant film becomes too thin to separate surfaces, leading to metal-to-metal contact, increased wear, and potential seizure.

Can kinematic viscosity be too high?

Yes. Excessive viscosity increases fluid friction, power consumption, operating temperature, and causes poor cold-starting. It can also lead to cavitation in hydraulic systems.

What is the kinematic viscosity of SAE 30 at 100C?

SAE 30 requires kinematic viscosity between 9.3 and 12.5 cSt at 100C per SAE J300. Typical values are around 11 cSt.

What is the kinematic viscosity of SAE 40?

SAE 40 requires kinematic viscosity between 12.5 and 16.3 cSt at 100C. Typical values around 14-15 cSt.

How does pressure affect kinematic viscosity?

Kinematic viscosity increases with pressure due to both increased dynamic viscosity and increased density. The density increase is modest (5-15% at 1 GPa) compared to dynamic viscosity (10-100x increase).

What is the Saybolt Universal Second?

SUS is the time in seconds for 60 mL of fluid to flow through a standardized Saybolt viscometer orifice at a specified temperature (typically 100F or 210F).

How do I convert SUS to cSt?

Approximate: cSt = SUS / 4.667 at 100F. More precise formulas exist for different viscosity ranges. For SUS below 100: cSt = SUS x 0.226 - 195/SUS. For SUS above 100: cSt = SUS x 0.220.

What is the kinematic viscosity of hydraulic oil?

Hydraulic oils range from ISO VG 10 (10 cSt at 40C) for low-temperature systems to ISO VG 68 (68 cSt) for high-pressure industrial systems. ISO VG 46 is the most common.

What is the significance of 40C and 100C in viscosity measurement?

40C represents typical industrial operating temperature. 100C represents hot engine or gearbox conditions. These two points define the viscosity-temperature curve for VI calculation.

How does dissolved gas affect kinematic viscosity?

Dissolved gas slightly reduces kinematic viscosity. Air entrainment (bubbles) can severely affect measurements, which is why samples should be degassed before testing.

What is a kinematic viscosity standard?

Certified reference fluids with precisely known kinematic viscosity at multiple temperatures, used to calibrate viscometers. NIST provides standards traceable to SI units.

How do I determine the correct viscosity for a bearing?

Calculate the required viscosity at operating temperature based on bearing size, speed, and load. Use the nu1 value from bearing manufacturers. The ratio of actual to required viscosity (kappa) indicates lubrication adequacy.

What is the kinematic viscosity of grease base oil?

Grease is a thickener dispersed in base oil. The base oil kinematic viscosity (typically 100-1000 cSt at 40C) determines the grease lubricating properties, not the grease consistency.

How does oxidation affect kinematic viscosity?

Oxidation increases kinematic viscosity as the oil thickens. A 20% increase from new-oil baseline is a typical alarm limit. Monitoring viscosity change is a key part of oil analysis programs.

What is the most accurate way to measure kinematic viscosity?

Capillary viscometers (ASTM D445 / ISO 3104) with precision better than 0.1% for Newtonian fluids at controlled temperature. Automated viscometers with multiple capillaries improve throughput and accuracy.

What is the future of kinematic viscosity measurement?

Trends include in-line process viscometers, microfluidic lab-on-chip devices for small samples, and machine learning models predicting viscosity from chemical composition for formulation optimization.

Related Calculators

Explore more calculators related to this topic.

Related Guides

Deepen your understanding with these educational resources.

Kinematic Viscosity Measurement Guide

ASTM guide to viscosity measurement

Lubricant Selection by Viscosity Grade

Practical guide from ExxonMobil

Understanding Viscosity Classifications

Educational resource from STLE

Glossary

Technical terms used in mortgage calculations explained in plain language.

ASTM D445: Standard test method for kinematic viscosity of transparent and opaque liquids using capillary viscometers.
Centistoke (cSt): CGS unit of kinematic viscosity. 1 cSt = 1 mm2/s = 10^-6 m2/s.
Dynamic Viscosity: Measure of internal resistance to shear flow. SI unit: Pa-s.
ISO VG: ISO Viscosity Grade - classification system based on kinematic viscosity at 40C.
Kinematic Viscosity: Ratio of dynamic viscosity to density. SI unit: m2/s. Common unit: cSt.
SAE J300: SAE standard for engine oil viscosity classification.
SUS: Saybolt Universal Seconds - empirical US viscosity unit.
Stoke (St): CGS unit of kinematic viscosity. 1 St = 100 cSt = 10^-4 m2/s.
Viscosity Index (VI): Measure of how much viscosity changes with temperature.
Viscosity Standard: Certified reference fluid with known viscosity for viscometer calibration.

Authoritative References

Trusted sources and standards referenced by this calculator.

ASTM D445 - Kinematic Viscosity Test Method ISO 3104 - Petroleum Products: Kinematic Viscosity ISO 3448 - Viscosity Classification SAE J300 - Engine Oil Viscosity Classification CRC Handbook of Lubrication and Tribology STLE - Viscosity Educational Resources NIST - Viscosity Standards ASTM D2162 - Basic Calibration of Master Viscometers

Applicable Standards

ASTM D445ISO 3104ISO 3448SAE J300ASTM D2162DIN 51562DIN 53015

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Last Updated:

2026-07-30

Version:

2.0.0

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Free to use for educational and professional purposes.