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Dynamic & Kinematic Viscosity with Density

Convert between positive dynamic and kinematic viscosity using mass density at the same fluid conditions.

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

Dynamic viscosity 1 cP and density 1,000 kg/m³ give kinematic viscosity 1 cSt. These equal 1 mPa·s and 1 mm²/s respectively.

Kinematic viscosity = dynamic viscosity / mass density

Worked example

Enter these known values and leave the other values blank.

Fluid mass density
1000 kg/m³
Dynamic viscosity
1 cP
Kinematic viscosity
1 cSt

Assumptions and limitations

  • Density and both viscosity measures are strictly positive. Use values at the same temperature, pressure and composition.
  • One centipoise is 1 mPa·s; one centistokes is 1 mm²/s. These are different physical dimensions and cannot be converted without density.
  • For non-Newtonian fluids, an apparent dynamic viscosity also depends on the relevant shear conditions. This unit relationship does not provide a flow-curve model.
  • Customary units distinguish pound-mass per foot-second from pound-force seconds per square foot or square inch. Standard gravity is used for pound-force and slug definitions.

Common questions

Is 1 cP always equal to 1 cSt?

No. Their numerical values coincide only when density is 1 g/cm³, or 1,000 kg/m³.

Why does lower density increase kinematic viscosity?

For a fixed dynamic viscosity, dividing by a smaller positive density gives a larger kinematic viscosity.

References

Bookify uses exact customary mass and volume definitions for density units, replacing rounded factors in the reference. Customary viscosity units use exact pound-mass, pound-force and international-length definitions, replacing rounded factors.

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