Centistokes, abbreviated as cSt, measure the kinematic viscosity of a fluid. Centipoises, abbreviated cP, measure its absolute viscosity. Viscosity describes the forces within a fluid -- the more viscous a liquid is, the more slowly it flows (see reference 1). For example, honey is more viscous than water. Kinematic viscosity takes the density of the liquid into account, while absolute viscosity does not; you only need to know the density to convert between the two.

- Skill level:
- Moderate

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### Things you need

- Calculator
- Mass balance scale
- Graduated cylinder or liquid measuring cup that has markings for ml

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## Instructions

- 1
Weigh an empty graduated cylinder or measuring cup using the mass balance scale. Read the mass in grams and record the number.

- 2
Add liquid to the graduated cylinder or measuring cup until it reaches the 100ml mark.

- 3
Weigh the container of liquid using the mass balance scale; read and record its mass in grams.

- 4
Subtract the mass of the empty container from the mass of the filled container to find the mass of the liquid.

- 5
Divide the mass of the liquid by the 100ml volume to obtain the density in g/ml. For example, if the mass is 200g, divide 200g by 100ml to get 2g/ml.

- 6
Convert the density to units of g/cm^3 -- this is a one-to-one conversion, so if the density is 2g/ml, you will convert it to 2g/cm^3.

- 7
Multiply the density by the kinematic viscosity in cSt to obtain the absolute viscosity in cP. If the density is 2g/cm^3 and the kinematic viscosity is 3 cSt, you will multiply (2g/cm^3)*(3 cSt) to get 6 cP.

#### Tips and warnings

- Note that absolute and kinematic viscosity do not use the same units -- a centipoise is .01g/cm*s, but a centistoke is .01cm^2/s. (reference 1)
- Divide absolute viscosity by density to convert it to kinematic viscosity.