Poise-Stokes Converter

Created by Kenneth Alambra
Reviewed by Wojciech Sas, PhD candidate and Jack Bowater
Last updated: Sep 25, 2022

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. Learn more about squeezing pressure on a container with fluids by checking out our manometer calculator.

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 fuel droplets that will be sprayed out of an injection nozzle due to applied pressure.

Now that we know the difference between the two types of viscosities, let's go back to the measurement units. A poise (P), named after Jean Léonard Marie Poiseuille, who also derived the Poiseuille's law equation, has a value equivalent to 0.1 pascals-second (Pa⋅s). We can also equate 1 poise in terms of other units at values shown in this table:

1 poise (P)

100 centipoise (cP)

100 millipascal seconds (mPa⋅s)

0.1 pascal seconds (Pa⋅s)

0.00209 slugs per foot second (slug/(ft⋅s))

0.00209 pound force second per square foot (lbf⋅s/ft²)

0.06720 pounds per foot second (lb/(ft⋅s))

1 dyne second per square centimeter (dyn⋅s/cm²)

1 grams per centimeter second (g/(cm⋅s))

0.1 kilogram per meter second (kg/(m⋅s))

0.0000145 reyn (reyn)

For kinematic viscosity, we measure it in terms of stokes. Stokes is named after Sir George Gabriel Stokes, who also derived Stokes' law. Learn more about it on our Stokes' law calculator. One stokes (St) is equivalent to 1 square centimeter per second (cm²/s). Here, we also have the other units which have a kinematic viscosity equal to 1 stoke:

1 stoke (St)

100 centistokes (cSt)

100 square millimeters per second (mm²/s)

1 square centimeter per second (cm²/s)

0.00010 square meters per second (m²/s)

0.15500 square inches per second (in²/s)

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.

💡 You can check out the Lookup density feature of our density calculator for the densities of some common liquids.

Once we know that, we can then use the following formula for conversion:

ν=η/ρν = η/ρ

where:

  • ν - Kinematic viscosity in stokes (St);
  • η - Dynamic viscosity in poise (P); and
  • ρ - Density in grams per cubic centimeter (g/cm³).

We may also see this formula expressed in the form:

νT=ηT/ρTν_\text{T} = η_\text{T} / ρ_\text{T}

In this form, the subscripted T denotes that we can only observe these parameters in a particular fluid at a specific temperature. That indicates that the fluid's density, hence its viscosity, too, changes depending on the fluid's temperature. For simplicity, we'll be using the form without the subscripted T.

Using our conversion formula, we can derive the formula to convert stokes to poise. We only need to multiply both sides of the equation by the density, ρ, to get:

η=ρ×νη = ρ \times ν

Now that we know how to convert poise to stokes, and vice versa, why don't we consider an example? 🙂

Example calculation

Let's say we want to convert the dynamic viscosity of water at 20ºC. At that temperature, water's density, ρ, is approximately 0.9982 g/cm³, and its dynamic viscosity, η, is around 0.010016 poise. Substituting these values in our formula, we have:

ν = 0.010016 poise / 0.9982 g/cm³

ν = 0.010034 stokes (St) or 1.0034 centistokes (cSt)

You can learn more about water viscosity and how temperature affects it by checking out our water viscosity calculator.

⚠️ When converting between the two types of viscosities, make sure you divide the dynamic viscosity in poise by the density in grams per cubic centimeters to obtain the kinematic viscosity in stokes. If these parameters are in different units, convert them first to these units to avoid miscalculations.

How to use the poise-stokes converter?

Using the poise-stokes calculator makes converting viscosity values a breeze. Here are the steps you can follow when using the poise-stokes converter:

  1. Enter the density of the fluid you're interested in.
  2. Input your known viscosity.

If you enter a value for the dynamic viscosity, you'll instantly see its equivalent kinematic viscosity, and vice versa. You can also convert dynamic and kinematic viscosity values to their other viscosity units using this converter. Simply type in the value of your known viscosity, and then choose another unit from the drop-down menu.

FAQ

What unit is used to measure viscosity?

We measure a fluid's viscosity in terms of poise for dynamic viscosity and stokes for kinematic viscosity. We can convert poise to stokes (or dynamic viscosities to kinematic viscosities) by dividing the value in poise by the fluid's density in grams per cubic centimeter.

How many stokes is in a poise?

Stokes is directly proportional to poise, with the fluid's density being the constant. By dividing a value of dynamic viscosity in poise by a density in grams per cubic centimeter, we get the kinematic viscosity value in stokes. If the fluid density is equal to 1 g/cm³, then the amount of kinematic viscosity in stokes will be the same as the dynamic viscosity in poise.

How do I convert stokes to poise?

To convert stokes to poise, you only have to multiply the value in stokes by the fluid density in units of grams per cubic centimeter. If you have a density value in terms of kilograms per cubic meter, you must first divide it by 1000 to get the density in grams per cubic centimeter before multiplying it by the viscosity in stokes.

What is kinematic viscosity?

Kinematic viscosity is a type of viscosity that tells us something about the speed of the fluid due to an applied force. This is a different type of viscosity than dynamic viscosity, which describes the amount of force required to move a particular fluid at a certain speed.

How much poise does 0.025 stokes diesel have?

To convert the kinematic viscosity of a particular mix of diesel from 0.025 stokes to poise:

  1. We first determine the density of diesel. Diesel has a density of 0.9 g/cm³.
  2. We then multiply the kinematic viscosity by this density. Therefore, we have 0.025 stokes × 0.9 g/cm³ to obtain 0.0225 poise as its equivalent dynamic viscosity.
Kenneth Alambra
ν = η/ρ
Density (ρ)
lb/cu ft
Dynamic viscosity (η)
cP
Kinematic viscosity (ν)
cSt
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