Viscometers for the measurement of viscosity under process conditions
in-line process viscometers
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centipoise
Units of viscosity

Dynamic viscosity

Poise (symbol: P)

Named after the French physician Jean Louis Marie Poiseuille (1799 - 1869), this is the cgs unit of viscosity, equivalent to dyne-second per square centimetre. It is the viscosity of a fluid in which a tangential force of 1 dyne per square centimetre maintains a difference in velocity of 1 centimetre per second between two parallel planes 1 centimetre apart.

Even in relation to high-viscosity fluids, this unit is most usually encountered as the centipoise (cP), which is 0.01 poise. Many everyday fluids have viscosities between 0.5 and 1000 cP.

Some typical viscosities (cP at 20°C)

air

0.02

motor oil SAE 20

125

acetone

0.3

motor oil SAE 50

540

methanol

0.6

castor oil

986

water

1.0

glycerin

1490

ethanol

1.2

pancake syrup

2500

mercury

1.5

maple syrup

3200

linseed oil (raw)

28

treacle

20,000

corn oil

72

peanut butter

250,000

olive oil

84

window putty

100,000,000

Pascal-second (symbol: Pa·s)

This is the SI unit of viscosity, equivalent to newton-second per square metre (N·s m–2). It is sometimes referred to as the poiseuille (symbol Pl).

One poise is exactly 0.1 Pa·s. One poiseuille is 10 poise or 1000 cP, while 1 cP = 1 mPa·s (one millipascal-second).

Table of equivalents

Dynamic viscosity
symbol
centipoise equivalent
1 kilogram-force second per square metre
kgf·s m–2

9 806.6501248

1 poundal second per square foot
pdl·s ft–2

1 488.164435

1 pound per foot hour
lb (ft·h)–1

0.4133789

1 pound per foot second
lb (ft·s)–1

1 488.1639328

1 pound-force second per square foot
lbf·s ft–2

47 880.2595148

1 pound-force second per square inch (reyn)
lbf·s in–2

6 894 757

1 slug per foot second
slug (ft·s)–1

47 880.25898

   

Kinematic viscosity

Stokes (symbol: St)

This is the cgs unit, equivalent to square centimetres per second (cm2 s–1). One stokes is equal to the viscosity in poise divided by the density of the fluid in grams per cubic centimetre (g·cm–3). It is most usually encountered as the centistokes (cSt), equal to 0.01 stokes.

 

Saybolt Seconds Universal (SSU)

This is the time for 60 millilitres (ml) of fluid to flow through the calibrated orifice of a Saybolt Universal viscometer at a specified temperature, as prescribed by test method ASTM D 88. For higher viscosities, SSF (Saybolt Seconds Furol) is used. “Furol” comes from “fuel and road oil”.

 

Degree Engler

This is the ratio of the time of flow of 200 ml of fluid to the time of flow of 200 ml of water at the same temperature in a standardized Engler viscosity meter.

Table of equivalents
Kinematic viscosity
symbol
centistokes equivalent
1 square centimetre per second
cm2 s–1

100

1 square metre per second
m2 s–1

1 000 000

1 square foot per second
ft2 s–1

92 903.04

1 square inch per second
in2 s–1

645.16

1 poise cubic foot per pound (not recommended!)
P·ft3 lb–1

6242.796

 

Centipoise - pascal second converter
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