About the Viscosity Converter
This viscosity converter handles both kinds of viscosity. Dynamic (absolute) viscosity — centipoise, poise, pascal-seconds and the imperial reyn — measures a fluid’s resistance to shear. Kinematic viscosity — centistokes, stokes, mm²/s and ft²/s — is dynamic viscosity divided by density, and is what gravity-flow viscometers and most lubricant datasheets report.
Within one kind the conversion is a fixed factor. Between the two kinds you need the fluid’s density at the same temperature, so enter it in kg/m³ (water is about 998, typical mineral oils 850–900, glycerine about 1,260). The density is ignored when both units are the same kind.
Use it to compare oil, hydraulic fluid, paint, resin or food-process specs, to translate a lab result into the units your pump or mixer supplier uses, or for fluid-mechanics coursework. Viscosity changes strongly with temperature, so always convert values measured at the same temperature.
How to use the viscosity converter
- 1Enter the viscosity value from your datasheet or measurement.
- 2Choose the unit it is in and the unit you need — dynamic and kinematic units are labelled.
- 3If you are converting between dynamic and kinematic, enter the fluid density at the same temperature.
- 4Read the result and the table of every unit.
Formula and method
Dynamic viscosity μ is measured in pascal-seconds in SI; the CGS poise is 0.1 Pa·s, so a centipoise equals exactly one millipascal-second. Kinematic viscosity ν is in m²/s; the CGS stokes is 1 cm²/s (10⁻⁴ m²/s), so a centistoke is exactly 1 mm²/s. Imperial units follow from their definitions: 1 lb/(ft·s) = 1.488164 Pa·s, 1 lbf·s/ft² = 47.88026 Pa·s, 1 reyn (lbf·s/in²) = 6,894.757 Pa·s, and 1 ft²/s = 0.09290304 m²/s.
Kinematic viscosity equals dynamic viscosity divided by density, ν = μ/ρ. With μ in cP and ρ in g/cm³ (specific gravity), that simplifies to cSt = cP ÷ SG. The converter turns your value into Pa·s or m²/s, crosses over with the density if needed, then divides by the size of each target unit.
- μ
- Dynamic viscosity (Pa·s, cP)
- ν
- Kinematic viscosity (m²/s, cSt)
- ρ
- Density (kg/m³)
- SG
- Specific gravity, density ÷ 1,000 kg/m³
Worked examples
100 cP oil to centistokes
100 cP is 0.1 Pa·s. Dividing by a density of 870 kg/m³ gives 1.149 × 10⁻⁴ m²/s, which is 114.94 cSt — the same as 100 ÷ 0.87.
50 cSt hydraulic fluid to centipoise
50 cSt = 50 × 10⁻⁶ m²/s. Multiplying by 850 kg/m³ gives 0.0425 Pa·s, or 42.5 cP (cP = cSt × SG = 50 × 0.85).
1 Pa·s in centipoise and poise
One pascal-second is 1,000 cP or 10 poise. It is also 1 ÷ 1.488164 = 0.672 lb/(ft·s).
1 ft²/s in centistokes
One square foot is 0.09290304 m², so 1 ft²/s = 0.09290304 m²/s = 92,903 mm²/s = 92,903 cSt. No density is needed because both units are kinematic.
Frequently asked questions
How do I convert cP to cSt?+
Divide centipoise by the fluid’s specific gravity: cSt = cP ÷ SG. For water (SG ≈ 1) the numbers are almost equal; for an oil with SG 0.87, 100 cP is about 115 cSt.
What is the difference between dynamic and kinematic viscosity?+
Dynamic viscosity measures internal resistance to shear (how hard it is to stir). Kinematic viscosity is that divided by density and describes how fast a fluid flows under gravity, which is what capillary viscometers measure.
Is a centipoise the same as mPa·s?+
Yes. One centipoise equals exactly one millipascal-second, so 1 cP = 1 mPa·s = 0.001 Pa·s. Water at 20 °C is about 1.0 cP.
Is a centistoke the same as mm²/s?+
Yes. One centistoke is exactly one square millimetre per second (10⁻⁶ m²/s). Lubricant grades such as ISO VG 46 are defined by their kinematic viscosity in mm²/s at 40 °C.
Can I convert SUS (Saybolt seconds) here?+
No. Saybolt Universal Seconds are an empirical flow-time scale with a non-linear, temperature-specific relation to centistokes (defined in ASTM D2161), so they cannot be converted with a single factor.