What is the difference between dynamic and kinematic viscosity?

Dynamic viscosity (µ) is the intrinsic resistance to shear flow. Kinematic viscosity (ν = µ/ρ) includes density effects — it describes how fast momentum diffuses. In the Navier-Stokes equations, kinematic viscosity appears naturally.

Why are cP and cSt used instead of SI units?

Water at 20°C has µ ≈ 1 cP and ν ≈ 1 cSt, making these convenient "human-scale" units. SI Pa·s values are very small numbers for common fluids.

What is Saybolt viscosity?

Saybolt Universal Seconds (SUS) measures the time for 60 mL of fluid to flow through a calibrated orifice. It is used in petroleum industry standards, especially ASTM specifications for lubricants.

How does temperature affect viscosity?

For liquids, viscosity decreases exponentially with temperature (Arrhenius-type behavior). Water's viscosity drops from 1.79 cP at 0°C to 0.28 cP at 100°C. For gases, viscosity increases with temperature.

What is non-Newtonian viscosity?

Non-Newtonian fluids (blood, paint, ketchup) have viscosity that changes with shear rate. The viscosity values in This calculator assume Newtonian behavior — constant viscosity regardless of shear rate.

How does viscosity relate to Reynolds number?

Re = ρVL/µ = VL/ν. Lower viscosity (or kinematic viscosity) means higher Re for the same flow conditions, making turbulence more likely. Viscous fluids tend to stay laminar.

Poise & Stokes Viscosity Converter

Convert between dynamic (Poise, Pa·s, cP) and kinematic (Stokes, cSt, mm²/s) viscosity units. Includes Saybolt conversion and common fluid reference table.

Conversion Mode

Dynamic Viscosity (mPa·s / cP)

Density (kg/m³)

Dynamic (mPa·s)

1.0020

= centipoise (cP)

Dynamic (Pa·s)

1.0020e-3

SI unit

Dynamic (Poise)

0.010020

CGS: 1 P = 0.1 Pa·s

Kinematic (mm²/s)

1.0038

= centistokes (cSt)

Kinematic (m²/s)

1.0038e-6

SI unit

Kinematic (Stokes)

0.010038

CGS: 1 St = 10⁻⁴ m²/s

Saybolt (SUS)

29.5

Approximate conversion

Re (sample)

9,962

1 m/s in 10mm pipe

Viscosity Scale (log)

1.00 cP (scale: 10⁻² to 10⁴)

Common Fluid Viscosities

Fluid	µ (mPa·s)	ν (mm²/s)	ρ (kg/m³)
Water (20°C)	1.002	1.004	998.2
Water (60°C)	0.467	0.475	983.2
Ethanol (20°C)	1.2	1.52	789
Glycerol (25°C)	934	742	1261
Motor Oil SAE 10W-30	100	115	870
Air (20°C)	0.01813	15.06	1.204
Mercury (25°C)	1.526	0.1126	13546
Honey	5000	3650	1370

Planning notes, formulas, and examples

About the Poise & Stokes Viscosity Converter

Viscosity describes a fluid's resistance to flow. Dynamic viscosity (µ) relates shear stress to strain rate and is measured in Pascal-seconds (Pa·s) or Poise (P). Kinematic viscosity (ν = µ/ρ) is the dynamic viscosity divided by density and is measured in m²/s or Stokes (St).

In practice, centipoise (cP = mPa·s) and centistokes (cSt = mm²/s) are the most commonly used units. Water at 20°C has a dynamic viscosity of exactly 1.002 cP — this is the historical reason for the centipoise unit.

This converter handles all common viscosity unit conversions: Pa·s, mPa·s, Poise, centipoise, m²/s, mm²/s, Stokes, centistokes, and Saybolt Universal Seconds (SUS). It also computes a sample Reynolds number to illustrate the flow regime implications.

Preset buttons load properties for water, honey, motor oil, air, and mercury. A reference table lists viscosities for eight common fluids, making This calculator invaluable for fluid dynamics, chemical engineering, and lubrication analysis.

When This Page Helps

Viscosity unit conversions are constantly needed in fluid mechanics, chemical engineering, and lubrication. Different industries and countries use different units, making conversion essential.

This calculator eliminates errors by converting all units simultaneously and providing a reference table for quick lookups.

How to Use the Inputs

Choose conversion direction: dynamic → kinematic or kinematic → dynamic.
Enter the viscosity value in mPa·s (cP) or mm²/s (cSt).
Enter the fluid density in kg/m³.
Read results in all common viscosity units.
Use presets to quickly load properties for common fluids.
Compare with the reference table for typical fluid viscosities.

Formula used

ν = µ/ρ (kinematic from dynamic).
1 Pa·s = 10 P = 1000 mPa·s = 1000 cP.
1 m²/s = 10⁴ St = 10⁶ mm²/s = 10⁶ cSt.
SUS ≈ 4.6·cSt + 25/cSt (for cSt < 50).
SUS ≈ 4.6·cSt (for cSt > 50).

Example Calculation

Result: ν = 1.004 cSt = 1.004×10⁻⁶ m²/s

Water at 20°C: ν = 1.002×10⁻³ Pa·s / 998.2 kg/m³ = 1.004×10⁻⁶ m²/s = 1.004 cSt.

Tips & Best Practices

Water at 20°C: µ = 1.002 cP, ν = 1.004 cSt — a convenient reference point.
For unit conversion: 1 cP = 1 mPa·s, 1 cSt = 1 mm²/s — these pairs are numerically identical.
Petroleum viscosities are often reported in Saybolt seconds — convert to cSt first for engineering calculations.
Viscosity index (VI) measures how much a lubricant's viscosity changes with temperature — higher VI is better.
Dynamic viscosity is what you need for pump sizing; kinematic viscosity is what you need for pipe flow Re.

When To Use This Calculator

Convert between dynamic (Poise, Pa·s, cP) and kinematic (Stokes, cSt, mm²/s) viscosity units. Includes Saybolt conversion and common fluid reference table. Use it when you need a repeatable calculation in the physics / general category and want the setup, result, and supporting values kept together. This is especially helpful when small input changes, unit choices, or rounding decisions can change the final number.

How To Check The Result

Start by confirming that the inputs match the formula shown on the page. Then compare the main output with the worked example and any secondary values shown by the calculator. If the result will be used in another calculation, keep extra precision until the final step and record the assumptions beside the number.

Practical Notes

Treat the result as a calculation aid rather than a substitute for context. For schoolwork, include the formula and substitution steps. For planning, technical, financial, or health-related decisions, verify important numbers against primary records, current rules, or a qualified professional before acting on them.

Sources & Methodology

Last updated: January 15, 2025

Frequently Asked Questions

Dynamic viscosity (µ) is the intrinsic resistance to shear flow. Kinematic viscosity (ν = µ/ρ) includes density effects — it describes how fast momentum diffuses. In the Navier-Stokes equations, kinematic viscosity appears naturally.