Viscosity Explained: Dynamic vs Kinematic

Why does honey crawl off a spoon while water splashes out of the glass? The answer is viscosity, and glycerine at room temperature is about 1,490 times more viscous than water.

This guide explains what viscosity measures and how its units fit together. You will see why datasheets quote two different kinds of viscosity. You will also learn why a warm liquid pours faster than a cold one.

Viscosity as a Fluid’s Internal Friction

Viscosity is how strongly a fluid resists flowing. Think of a liquid as thin layers sliding over each other. A thick liquid drags hard on the next layer, while a thin one lets it slip past easily.

HyperPhysics describes the classic test. You pull a flat plate through a liquid at a steady speed. The force you need grows with the plate’s area and with how fast the speed changes across the liquid. The constant linking them is the viscosity.

That is why the SI unit is the pascal-second. A pascal is a unit of stress, one newton per square meter. Our guide to pressure units like psi, bar and Pa explains it in more detail. Multiply that stress by a time, and you get Pa s.

The range is enormous. Air at 20 C sits near 0.018 cP. Water is about 1 cP, heavy oil about 660 cP, and glycerine about 1,490 cP. The chart below uses a log scale, so each gridline is ten times the one before.

How Do Pa s, Poise and Centipoise Relate?

One pascal-second equals 10 poise, and one poise equals 100 centipoise. So one centipoise is exactly 0.001 Pa s, the same as one millipascal-second.

The older poise comes from the centimeter-gram-second system. It survives because the centipoise lands so close to water. At 20 C, water measures 1.0016 cP, so a datasheet in cP reads almost like “times thicker than water.”

Take the tool page’s own example: convert 1 cP to pascal-seconds. The answer is 0.001 Pa s, which is also 1 mPa s. Going the other way, 0.5 Pa s is 500 cP.

The imperial pound-force second per square foot is huge. One of them equals 47.88 Pa s, or 47,880 cP. The pound per foot second is much smaller, at 1.488 Pa s. The two imperial units differ by a factor of about 32.17, so read the label carefully in older engineering texts.

Dynamic vs Kinematic Viscosity: Which One Is on the Datasheet?

Dynamic viscosity measures resistance to shear, while kinematic viscosity is dynamic viscosity divided by density. Check the unit: Pa s or cP means dynamic, and m^2/s, stokes or cSt means kinematic.

Density is the only link between the two numbers. Two liquids with the same dynamic viscosity get different kinematic values when one is denser. Our article on density with everyday examples covers the mass-per-volume side of this formula.

NIST lists the kinematic units. One stokes is 0.0001 m^2/s, and one centistokes is 0.000001 m^2/s, which is 1 mm^2/s.

Converting Water From cP to cSt

1. Start with dynamic viscosity. Water at 20 C is 1.0016 cP, which is 0.0010016 Pa s.
2. Find the density. The same water has a density of 0.9982 g/cm^3, or 998.2 kg/m^3.
3. Divide in SI units. 0.0010016 divided by 998.2 gives 0.0000010034 m^2/s.
4. Convert to centistokes. Divide by 0.000001 to get 1.0034 cSt, matching the HyperPhysics table.
5. Use the shortcut next time. cP divided by density in g/cm^3 gives cSt directly.

Try the shortcut on a made-up oil of 90 cP with a density of 0.9 g/cm^3. It comes out to 100 cSt. Water barely changes because its density is so close to 1 g/cm^3.

Our calculator handles dynamic units only. It does not divide by density, so do that step by hand for any cSt figure.

Why Does Temperature Change Viscosity So Much?

Warm liquid molecules move faster and hold each other less tightly, so the liquid flows more easily. For water, the effect is large while the density barely moves.

The HyperPhysics water table, built on 2008 international reference data, shows the pattern. Water is 1.3059 cP at 10 C and 0.6527 cP at 40 C, so it halves over those 30 degrees. At 80 C it drops to 0.354 cP, about 35 percent of its 20 C value.

Even a small change matters. From 20 C to 25 C, water falls from 1.0016 cP to 0.89 cP, a drop of about 11 percent. A lab that reports a result at the wrong temperature can be off by more than a tenth.

This is why every viscosity number needs a temperature beside it. A figure of “1 cP” means little without “at 20 C.”

A Brief Word on Motor Oil Grades

Motor oil labels such as 5W-30 name a viscosity grade, and each engine calls for a specific one. FuelEconomy.gov reports that 10W-30 in an engine designed for 5W-30 can lower gas mileage by 1 to 2 percent. Using the grade your owner’s manual lists avoids that loss.

Unit Slips That Skew Viscosity Numbers

A single unit slip can shift a viscosity result by a factor of 10, 100 or 1,000. The table pairs each trap with a safer habit.

Blood is a good reminder of the temperature rule. HyperPhysics lists whole blood at about 4 cP, but that figure is measured at body temperature, 37 C, not at 20 C.

Try it with a value from your own datasheet. Enter it in the viscosity unit converter to see the same number in Pa s, poise and centipoise.

Viscosity: Frequently Asked Questions

Sources and Further Reading

This article explains viscosity and its units for learning and everyday engineering work. Real fluids vary with temperature, pressure and composition, so check a datasheet for critical jobs. Reviewed for accuracy by Prof. Dr. Khalil Mudassar, PhD. Last updated September 27, 2026.