Poise-Stokes converter
This poise-stokes converter will help you easily convert dynamic viscosity to kinematic viscosity and vice versa. In this stokes to poise calculator, you will learn:
- The difference between dynamic and kinematic viscosity;
- The relationship between these two types of viscosities; and
- How to convert poise to stokes, stokes to poise, or either to other viscosity units.
Keep on reading to start learning!
Poise and stokes viscosity units
Poise and stokes are units of measure used to quantify viscosity. Poise is a unit of measurement used particularly for dynamic viscosity, while stokes is for kinematic viscosity. Viscosity, which describes a fluid's consistency or "thickness," comes in these two types for some distinct reasons.
The dynamic viscosity tells us how much force is required for a fluid to move at a particular speed. When formulating the mixture of, let's say, a paste in a tube, we want the paste to have a specific dynamic viscosity. That way, it won't be either too hard to squeeze the paste out of the tube or too runny that a lot of paste comes out, even with a little squeezing pressure.
On the other hand, we use kinematic viscosity to describe the speed of the fluid due to an applied force. One particular use of kinematic viscosity is for fuels. By determining the viscosity of fuels in terms of kinematic viscosity, we get to model the speed of fuel droplets that will be sprayed out of an injection nozzle due to applied pressure.
A poise (P), named after Jean Léonard Marie Poiseuille, who also derived Poiseuille's law equation, has a value equivalent to 0.1 pascal-second (Pa·s). We can also equate 1 poise in terms of other units:
| 1 poise (P) | 100 centipoise (cP) |
| 1 poise (P) | 100 millipascal seconds (mPa·s) |
| 1 poise (P) | 0.1 pascal seconds (Pa·s) |
| 1 poise (P) | 0.00209 slugs per foot second (slug/(ft·s)) |
| 1 poise (P) | 0.00209 pound force second per square foot (lbf·s/ft²) |
| 1 poise (P) | 0.06720 pounds per foot second (lb/(ft·s)) |
| 1 poise (P) | 1 dyne second per square centimeter (dyn·s/cm²) |
| 1 poise (P) | 1 gram per centimeter second (g/(cm·s)) |
| 1 poise (P) | 0.1 kilogram per meter second (kg/(m·s)) |
For kinematic viscosity, we measure it in terms of stokes. Stokes is named after Sir George Gabriel Stokes, who also derived Stokes' law. One stokes (St) is equivalent to 1 square centimeter per second (cm²/s). Here are other units that have a kinematic viscosity equal to 1 stoke:
| 1 stoke (St) | 100 centistokes (cSt) |
| 1 stoke (St) | 100 square millimeters per second (mm²/s) |
| 1 stoke (St) | 1 square centimeter per second (cm²/s) |
| 1 stoke (St) | 0.00010 square meters per second (m²/s) |
| 1 stoke (St) | 0.15500 square inches per second (in²/s) |
| 1 stoke (St) | 0.00108 square feet per second (ft²/s) |
💡 For practical reasons, we usually use centipoise and centistokes as units for dynamic and kinematic viscosities, respectively.
How to convert poise to stokes
We may want to express the viscosity values from one type to another in some cases. Converting from poise to stokes, and even from stokes to poise, is quite an easy thing to do. However, to do that, we need the density of the fluid in question.
The relationship between dynamic viscosity (μ) and kinematic viscosity (ν) is given by:
ν = μ / ρ
where ρ is the density of the fluid.
Using the CGS units directly, the conversion is especially neat — with the density expressed in grams per cubic centimeter (g/cm³):
- Poise → Stokes: ν (St) = μ (P) / ρ (g/cm³)
- Stokes → Poise: μ (P) = ν (St) × ρ (g/cm³)
Example calculation
Suppose a fluid has a dynamic viscosity of 2 poise and a density of 0.8 g/cm³ (800 kg/m³). To find its kinematic viscosity in stokes:
ν = μ / ρ = 2 P / 0.8 g/cm³ = 2.5 St = 250 cSt = 0.00025 m²/s
To go the other way, multiply instead of divide. A fluid with a kinematic viscosity of 2.5 St and a density of 0.8 g/cm³ has a dynamic viscosity of 2.5 × 0.8 = 2 P.
How to use the poise-stokes converter
- Choose the conversion direction — poise to stokes (dynamic → kinematic) or stokes to poise (kinematic → dynamic).
- Enter the viscosity value and pick the unit it is expressed in (P, cP, Pa·s, mPa·s, lbf·s/ft², St, cSt, m²/s, mm²/s, ft²/s, and more).
- Select a fluid preset or enter the density manually in your preferred unit (g/cm³, kg/m³, lb/ft³, or slug/ft³). The converter supports both the metric and American (imperial) measurement systems.
- Read the result — the converter shows the value in every common dynamic and kinematic viscosity unit at once.
FAQs
What is the difference between poise and stokes?
Poise measures dynamic (absolute) viscosity — the internal friction of a fluid. Stokes measures kinematic viscosity — the dynamic viscosity divided by the fluid's density. They are linked by ν = μ / ρ.
Can I convert poise to stokes without the density?
No. Because kinematic viscosity is dynamic viscosity divided by density, you always need the density of the fluid to convert between poise and stokes.
How many centipoise are in one poise?
There are 100 centipoise (cP) in 1 poise (P), and likewise 100 centistokes (cSt) in 1 stokes (St). Centipoise and centistokes are the units most often used in practice.
What is 1 poise in SI units?
1 poise equals 0.1 pascal-second (Pa·s), or equivalently 100 millipascal-seconds (mPa·s).