Viscosity Converter
Convert dynamic viscosity (centipoise, Pa·s, poise, reyn) and kinematic viscosity (centistokes, m²/s, stokes, SUS). Enter the fluid density to convert between the two, for example cP to cSt, or pick a common fluid to fill in typical values.
Last updated:
Water ≈ 1.0 g/cm³, typical mineral oil ≈ 0.85–0.90
How to use the Viscosity Converter
- Enter the viscosity value.
- Choose the From and To units; dynamic and kinematic units are labeled.
- Enter the fluid density if you are converting between dynamic and kinematic (for example cP to cSt).
- Read the result plus the cP, cSt and SUS equivalents and the full unit table.
- Tap a fluid preset to try typical values, or copy the results.
Dynamic vs kinematic viscosity
Dynamic (absolute) viscosity, μ, is a fluid's resistance to shearing: how hard it is to slide one layer past another. Its SI unit is the pascal-second (Pa·s); the everyday unit is the centipoise (cP), which equals one millipascal-second. Water at 20 °C is almost exactly 1 cP.
Kinematic viscosity, ν, is dynamic viscosity divided by density. It describes how fast a fluid flows under its own weight, which is why gravity-flow instruments (capillary tubes, Saybolt and Ford cups) measure it. Its SI unit is m²/s; the practical unit is the centistokes (cSt), equal to 1 mm²/s. Motor oil and hydraulic fluid grades are specified in cSt.
ν (cSt) = μ (cP) ÷ ρ (g/cm³) and μ (cP) = ν (cSt) × ρ (g/cm³)
Example: an oil of 100 cP with a density of 0.87 g/cm³ has a kinematic viscosity of 100 ÷ 0.87 = 114.9 cSt. Because the density is close to 1 for many liquids, cP and cSt numbers are often similar, but not identical; mercury (13.5 g/cm³) is a dramatic exception.
Viscosity unit factors
| Unit | Equals |
|---|---|
| 1 poise (P) | 100 cP = 0.1 Pa·s |
| 1 centipoise (cP) | 1 mPa·s = 0.001 Pa·s |
| 1 lb/(ft·s) | 1.48816 Pa·s = 1,488.16 cP |
| 1 lbf·s/ft² | 47.8803 Pa·s |
| 1 reyn (lbf·s/in²) | 6,894.76 Pa·s |
| 1 stokes (St) | 100 cSt = 1 cm²/s = 0.0001 m²/s |
| 1 centistokes (cSt) | 1 mm²/s = 10⁻⁶ m²/s |
| 1 ft²/s | 92,903.04 cSt |
| SUS (Saybolt Universal Seconds) | Non-linear; about 4.63 × cSt above roughly 75 cSt (at 100 °F) |
Saybolt Universal Seconds are the time for 60 mL of fluid to flow through a standard orifice. The tool uses the ASTM D2161 equation for 100 °F (37.8 °C), valid from about 1.8 cSt (32 SUS) upward.
Approximate viscosity of common fluids
| Fluid (about 20 °C) | Dynamic (cP) | Density (g/cm³) | Kinematic (cSt) |
|---|---|---|---|
| Air (sea level) | 0.018 | 0.0012 | ≈ 15 |
| Gasoline | ≈ 0.6 | ≈ 0.74 | ≈ 0.8 |
| Water | 1.00 | 0.998 | 1.00 |
| Ethanol | 1.2 | 0.789 | 1.5 |
| Mercury | 1.55 | 13.53 | 0.11 |
| Olive oil | ≈ 84 | 0.91 | ≈ 92 |
| Glycerin | ≈ 1,400 | 1.26 | ≈ 1,120 |
| Honey | 2,000–10,000 | ≈ 1.42 | 1,400–7,000 |
Viscosity changes strongly with temperature: liquids get thinner as they warm up (water is about 0.65 cP at 40 °C), so always note the temperature of a measurement. Values above are typical, rounded figures.
Frequently asked questions
How do I convert cP to cSt?
Divide centipoise by the fluid density in g/cm³: cSt = cP ÷ ρ. A 100 cP oil with density 0.87 g/cm³ is 100 ÷ 0.87 = 114.9 cSt. For water (ρ ≈ 1), cP and cSt are nearly equal.
What is the difference between dynamic and kinematic viscosity?
Dynamic viscosity (cP, Pa·s) measures resistance to shear. Kinematic viscosity (cSt, m²/s) is dynamic viscosity divided by density and describes flow under gravity. You need the density to convert between them.
How many centipoise is 1 Pa·s?
1 Pa·s = 1,000 cP = 10 poise. One centipoise equals one millipascal-second (mPa·s).
How do I convert SUS to cSt?
Saybolt Universal Seconds are related to cSt by the ASTM D2161 equation, which is non-linear at low viscosity. Above about 75 cSt, SUS ≈ 4.632 × cSt (at 100 °F). This tool applies the full equation in both directions.
What is the viscosity of water?
About 1.00 cP (1 mPa·s) and 1.00 cSt at 20 °C. It drops to about 0.65 cP at 40 °C and 0.28 cP at 100 °C.
Is a stokes the same as a poise?
No. The poise is a unit of dynamic viscosity (0.1 Pa·s); the stokes is a unit of kinematic viscosity (1 cm²/s). They are linked by density: poise = stokes × density in g/cm³.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.